US20060227580A1 - Programmable power supply - Google Patents

Abstract

A progammable power supply for providing a regulated DC output power is disclosed. The power supply provides the output power to any one of a plurality of electronic devices adapted for receiving the output power at an operational voltage or an operational current. The power supply receives a programming signal to maintain the output power at the operational voltage or operational current associated with a particular selected electronic device. Accordingly, by varying the programming signal, the power supply can be programmed to provide output power to any one of several electronic devices having differing input power requirements.

Description

RELATED APPLICATIONS
• This application is a continuation application of utility application Ser. No. 11/154,199, filed Jun. 16, 2005, which is a continuation application of utility application Ser. No. 10/927,566, filed Aug. 26, 2004, now U.S. Pat. No. 6,922,347, which is a divisional application of utility application Ser. No. 10/313,793, filed Dec. 5, 2002, now U.S. Pat. No. 6,809,943, which is a continuation application of utility application Ser. No. 10/140,513, filed May 2, 2002, now U.S. Pat. No. 6,693,413, which is a continuation application of utility application Ser. No. 09/694,972, now abandoned, which is a continuation-in-part application of utility application Ser. No. 09/310,461 filed on May 12, 1999, now U.S. Pat. No. 6,172,884, which is a continuation-in-part application of utility application Ser. No. 09/148,811, filed on Sep. 4, 1998, now U.S. Pat. No. 5,949,213, which is a continuation-in-part application of utility application Ser. No. 09/148,811, filed Sep. 4, 1998, now U.S. Pat. No. 6,091,611, which is a continuation application of utility application Ser. No. 08/994,905, filed Dec. 19, 1997, now U.S. Pat. No. 5,838,554, which is a continuation-in-part of utility application Ser. No. 08/767,307 filed Dec. 16, 1996, now abandoned, which is a continuation-in-part application of utility application Ser. No. 08/567,369 filed Dec. 4, 1995, now U.S. Pat. No. 5,636,110 and claims priority of provisional application Ser. No. 60/002,488 filed Aug. 17, 1995, and is also a continuation-in-part application of utility application Ser. No. 08/233,121 filed Apr. 26, 1994, now U.S. Pat. No. 5,479,331.
NOTICE OF COPYRIGHTS
• A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the United States Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention relates to power supplies and in particular relates to power supplies for use with a variety of different devices.
• 2. Background of the Invention
• Prior art power supplies include a variety of techniques, particularly those used for powering microelectronics such as the class of computers commonly known as “notebook” computers such as the Powerbook Series available from Apple Computer of Cupertino California and the Thinkpad Series available from International Business Machines (IBM) of Armonk, N.Y. More recently, even smaller personal computers referred to as “sub-notebooks” have also been developed by various companies such as Hewlett-Packard's Omnibook. The goal of these notebooks and sub-notebooks designs is to reduce the size and weight of the product. Currently, notebooks typically weigh about six pounds and sub-notebooks weigh slightly less than four pounds.
• Many of these notebook and sub-notebook computers have a battery that must be recharged. Also, typically the computers are designed to be operated from external power sources such as line current and the electrical power system of automobiles.
• To power these computers, the manufacturer typically provides an external power source. The external power source may be a switching power supply that may weigh close to a pound and may be about eight inches long, four inches wide and about four inches high. Smaller power supplies do exist but frequently they lack sufficient power to charge new batteries such as nickel hydride batteries.
• Such external power supplies therefore contribute substantial additional weight that the user of the computer must carry with him or her to permit battery charging and/or operation from an electrical socket. Further, the external power supply is bulky and may not be readily carried in typical cases for such notebook and sub-notebook computers. In addition, conventional power supplies often have difficulty providing the necessary power curve to recharge batteries that have been thoroughly discharged. Also, a power supply is needed for each peripheral device, such as a printer, drive or the like. Thus, a user needs multiple power supplies.
• While it has long been known to be desirable to reduce the size and weight of the power supply, this has not been readily accomplished. Many of the components such as the transformer core are bulky and have significant weight. Further, such power supplies may need to be able to provide DC power of up to seventy-five watts, thereby generating substantial heat. Due to the inherent inefficiencies of power supplies, this results in substantial heat being generated within the power supply. Reduction of the volume, weight and heat are all critical considerations for a power supply in this type of application and cannot be readily accomplished. In particular, it is believed to be desirable to have a package as thin as possible and designed to fit within a standard pocket on a shirt or a standard calculator pocket on a brief case. In addition, conventional power supplies are device specific and each device requires its own power supply. Therefore, users need multiple power supplies, which consumes space and increases unnecessary weight.
• Cellular telephones are also extensive users of batteries. Typically, cellular telephone battery chargers have been bulky and are not readily transportable. Moreover, cellular telephone battery chargers often take several hours, or more, to charge a cellular telephone battery.
SUMMARY OF THE INVENTION
• It is an object of an embodiment of the present invention to provide an improved small form factor power supply that is resistant to liquids and/or is programmable to supply power for a variety of different devices, which obviates for practical purposes, the above mentioned limitations.
• These and other objects are accomplished through novel embodiments of a power supply having a transformer. The primary portion includes a primary rectifier circuit, a controller, first and secondary primary drive circuits each coupled magnetically by a coil to the core and a primary feedback circuit magnetically coupled by a separate core. The secondary portion includes a secondary output circuit magnetically coupled by a coil to the core that provides the regulated DC output and a secondary feedback back circuit magnetically coupled to the second core to provide a signal to the primary feedback circuit. In alternative embodiments, different transformer topologies may be used.
• The controller provides a separate square wave signal to each of the two primary circuits and the phase of the square wave signals may be altered relative to each other as determined by the controller. The secondary circuit is positioned on the core relative to the two primary circuits so that the secondary circuit coil is positioned at a summing point on the core of the first and second primary circuit coils. The DC voltage and current levels produced at the output of the secondary circuit are monitored by the secondary feedback circuit to provide, through a secondary feedback coil and a primary feedback coil, a signal to the controller. The controller alters the phase between the signals driving the two coils to produce the desired output DC voltage and current at the secondary coils. This results in providing a regulated DC power supply with high efficiency.
• By mounting all of the components on a printed circuit board using planar or low profile cores and surface mounted integrated circuits, a small form factor power supply can be attained. Given the high efficiency of the conversion and regulation, the system minimizes dissipation of heat permitting the entire power supply to be mounted within a high impact plastic container dimensioned, for example, as a right parallelepiped of approximately 2.85×5.0×0.436 inches, thereby providing a power supply that can readily be carried in a shirt pocket. It should be understood that changes in the overall dimensions may be made without departing from the spirit and scope of the present invention. Making a relatively thin package having relatively large top and bottom surface areas relative to the thickness of the package provides adequate heat dissipation.
• Particular embodiments of the present invention utilize an improved transformer core that, by moving the relative position of the transformer legs, maximizes a ratio of the cross-sectional area of the transformer legs to the windings, thereby requiring less windings for the same magnetic coupling. Fewer windings means less area of a layer of a circuit board may be used so that the number of layers on the circuit board may be minimized. The improved transformer core also provides this maximized ratio while maintaining the ratio of the secondary and primary windings at a constant value. In alternative embodiments, different transformer topologies may be used.
• It is an object of an additional embodiment of the present invention to alleviate the need for having a separate power supply for providing power for using each portable electronic device having distinct power requirements.
• It is another object of the additional embodiment of the present invention to provide a power supply which is programmable to transmit an appropriate input power to any one of several electrically powered devices.
• Briefly, the additional embodiment of the present invention is directed to a power supply which is programmable for providing between about zero and seventy five watts of power DC to a portable electronic appliance adapted for receiving DC power at one of an operational current and an operational voltage. The power supply comprises an input circuit for receiving input power from a power source, an output circuit adapted for coupling to the electronic appliance at an output connection for transmitting power to the electronic appliance and a power conversion circuit for providing output power at the operational current or the operational voltage in response to a detection of one of a programming signal received at the output connection.
• The power supply may be configured to be programmable to support a variety of different devices and/or more than one device at a time. This may be accomplished with an on-board processor or by using external cables to provide the programming signal. Thus, the need for having multiple power supply devices (each adapted for meeting the power requirements of a distinct portable device) for providing power to different portable devices.
• Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.
BRIEF DESCRIPTION OF THE FIGURES
• A detailed description of embodiments of the invention will be made with reference to the accompanying drawings, wherein like numerals designate corresponding parts in the several figures.
• FIG. 1 is a block diagram of a first embodiment of the disclosed invention.
• FIG. 2 is a sectional view of the E core for use in the embodiments ofFIG. 1.
• FIG. 3 is a detailed circuit schematic of the embodiment ofFIG. 1.
• FIG. 4 is a top planar view of a printed circuit board containing the circuit ofFIG. 3.
• FIG. 5A is a top planar view of a case or housing for an additional embodiment of the for an invention where the case houses the other components.
• FIG. 5B is a partial cross-section of the louvers and openings of the case top as shown inFIG. 5A.
• FIG. 5C is a partial cross-section of another embodiment of the louvers formed from raised ridges and depressions on the case top.
• FIG. 6 is a top planar view of one of two heat sinks for the additional embodiment of the invention that sandwich a printed circuit board containing the circuitry for the additional embodiment.
• FIGS. 7A and 7B are a schematic diagram of the additional embodiment of the invention.
• FIG. 7C is a schematic diagram of a switch mechanism that may be used to select a resistor from among a plurality of resistors in order for the power supply to produce a desired output voltage or output current.
• FIG. 8 is a timing diagram for the circuit shown inFIGS. 7A and 7B.
• FIG. 9 is a block diagram of the U1 integrated circuit shown inFIG. 7.
• FIGS. 10A and B are timing diagrams for the block diagram shown inFIG. 9.
• FIG. 11 is a power versus output current curve and an output voltage versus current curve of a power supply in accordance with an embodiment of the present invention.
• FIGS. 12A-12C are a top plan view and two side plan views of a transformer core in accordance with another embodiment of the present invention.
• FIGS. 13A-13C are a top plan view and two side plan views of a transformer cap for use with the transformer core shown inFIGS. 12A-12C.
• FIG. 14 is a top plan view of a printed circuit board layer, without winding patterns, to be coupled with the transformer core shown inFIGS. 12A-12C.
• FIG. 15 is a top plan view of another printed circuit board layer showing a secondary winding pattern to be coupled with to the transformer core shown inFIGS. 12A-12C.
• FIG. 16 is a top plan view of another printed circuit board layer showing a primary winding pattern to be coupled with the transformer core shown inFIGS. 12A-12C.
• FIGS. 17A-17C are a top plan view and two side plan views of a transformer core in accordance with an alternative embodiment of the present invention.
• FIGS. 18A-18C are a top plan view and two side plan views of a transformer cap for use with the transformer core shown inFIGS. 17A-17C.
• FIG. 19 is a top plan view of a printed circuit board layer with a secondary winding pattern to be coupled with the transformer core shown inFIGS. 17A-17C.
• FIG. 20 is a top plan view of another printed circuit board layer showing primary winding patterns to be coupled with the transformer core shown inFIGS. 17A-17C.
• FIG. 21 is a top plan view of another printed circuit board layer showing additional primary winding patterns to be coupled with the transformer core shown inFIGS. 17A-17C.
• FIG. 22 is a top plan view of another printed circuit board layer showing a another secondary winding pattern to be coupled with the transformer core shown inFIGS. 17A-17C.
• FIG. 23 is a schematic of a control circuit in accordance with an embodiment of the present invention.
• FIG. 24 is a schematic of a programming circuit in accordance with an embodiment of the present invention that is used to digitally program the power supply to produce between 0 and 16 volts.
• FIG. 25 is a schematic of another programming circuit in accordance with an embodiment of the present invention that is used to digitally program the power supply to produce between 16 and 18 volts.
• FIG. 26 is an end view of a connector that mates with the small form factor power supply and is useable to program the small form factor power supply.
• FIGS.27(a)-27(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.28(a)-28(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.29(a)-29(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.30(a)-30(b) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.31(a)-31(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.32(a)-32(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.33(a)-33(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.34(a)-34(c) show a cable with connections in accordance with an embodiment of the present invention to program the small form factor power supply for supplying power to different devices;
• FIGS.35(a)-40(c) show various connector adapters four use with the cable shown above in FIGS.34(a)-34(c).
• FIGS.41(a) and41(b) illustrate a block diagram and a schematic of an interface for providing power to more than one device at a time.
• FIG. 42 shows a top and rear perspective view of a small form factor power supply for use with portable telephone equipment.
• FIG. 43 shows a top and front perspective view of the small form factor power supply shown inFIG. 42.
• FIG. 44 shows a bottom and front perspective view of the small form factor power supply shown inFIG. 42.
• FIG. 45 shows a side perspective view of the small form factor power supply shown inFIGS. 42-44 connected to a cellular telephone battery and telephone.
• FIG. 46 shows a top front perspective view of the small form factor power supply shown inFIGS. 42-44 connected to a cellular telephone battery and telephone.
• FIG. 47 shows a top and front perspective view of a small form factor power supply adapter connector for use with portable telephone equipment.
• FIG. 48 shows a top perspective view of the adapter connector shown inFIG. 47.
• FIG. 49 shows a bottom perspective view of the adapter connector shown inFIG. 47
• FIG. 50 shows a right side view of the adapter connector shown inFIG. 47.
• FIG. 51 shows a schematic diagram of an alternative embodiment of a power supply which receives input power from a DC source.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• As shown in the drawings for purposes of illustration, embodiments of the present invention are directed to an improved small form factor power supply. In preferred embodiments of the present invention, the small form factor power supply is packaged in a small volume and produces over 75 watts of power with temperatures below 140° F. Preferred embodiments are used to power portable computers. However, it will be recognized that further embodiments of the invention may be used with other electronic devices, such as computer peripherals, audio and video electronics, portable telephone equipment and the like.
• Other embodiments of the present invention are more generally directed to a power supply which is capable of providing power to any selected one of a number of electronic devices in response to a programming signal. Each of the electronic devices is adapted for receiving input power at either a set operational voltage or a set operational current. The programming signal preferably controls the power supply to maintain the output power at one of an operational current or an operational voltage associated with the selected electronic device.
• FIG. 1 shows a block diagram of the power supply according to an embodiment of the present invention. All components on the left side of amagnetic core20 are part of theprimary portion100 and all portions on the right hand side are part of thesecondary portion200 of the power supply.
• Theprimary portion100 includes a primary rectifier andinput circuit110, a first primary and drivecircuit120, a second primary and drivecircuit130, aprimary feedback circuit140 and acontroller150. Thesecondary portion200 includes asecondary output circuit210 and asecondary feedback circuit240.
• The function of the primary rectifier andinput circuit110 is to couple theembodiment10 to the line voltage (for example 110 volt, 60 Hz), to rectify that voltage and provide DC power for the remainder of theprimary portion100 and a ground path for theprimary circuits120 and130. Thecontroller150, which may be a Unitrode 3875 provides two square wave driver signals152 and154 having alterable phases to the first and the secondprimary circuits120 and130. The first and second primary circuits are resonant circuits that are resonant at about the frequency of the driver signals and include coils that are coupled to thecore20, which may be a planar or low profile “E” type core, which may be any low loss material, as is shown in a sectional view inFIG. 2. Hence, the driver signals are magnetically coupled to the core20 by first and second primary coils contained within thecircuits120,130.
• Thecoil212 in thesecondary circuit210 is preferably positioned relative to the coils of the two primary cores so that the coil in the secondary circuit is at a summing point of the magnetic flux from the primary circuit coils. If a planar or low profile “E” type core as shown inFIG. 2 is used, thecoil212 for thesecondary circuit210 is positioned about thecentral leg22. The coil for thefeedback circuits140 is positioned on one of theouter legs24,26. As a result, the magnetic flux from the two primary coils of theprimary circuits120,130 are summed at the position where thesecondary coil212 for thesecondary circuit210 is positioned. (This positioning of the coils is shown inFIG. 1 by using the double line to indicate thecentral leg22 and a single line to represent theouter legs24,26).
• The amplitude of the DC voltage and current produced by thesecondary circuit210 are monitored by thesecondary feedback circuit230. Theprimary feedback circuit140 and thesecondary feedback circuit230 are magnetically coupled by coils positioned on another core23 to provide a feedback signal to thecontroller150. In response to the feedback signal, the controller alters the relative phase between the twodriver signals152 and154 to obtain the desired magnitude of the voltage and current. Since thesecondary coil212 is located at a summing point on the core of the flux from the two primary coils, as the phase between the drivingsignals152 and154 to the two primary coils alters, the magnitude of the current and voltage induced in the secondary coil will vary. This will permit control of thesecondary circuit210 output voltage and current, thereby providing a readily controlled output voltage.
• FIG. 3 shows a more detailed schematic of an embodiment of the invention. A standard AC plug may be coupled to inputnodes111,112 to a first filter coil L1 that is coupled to a fullwave rectifier bridge113, which may be a MDA106G. Filtering capacitors C1, C2, C7, C8 are also coupled to thebridge113 and one side of the bridge is coupled to AC ground.
• The other side of the bridge is coupled to theprimary coils122 and132 of the first and secondprimary circuits120,130 respectively. The other terminal of theprimary coils122,132 are coupled to the remainder of theprimary circuits120 and130. Each of theseprimary circuits120,130 also comprise adrive field effect124,134, which may be a MTP6N60 and acapacitor126,136. Thecoils122,132,transistors124,134 andcapacitors126,136 are selected so that the resonant frequency of thecircuits120,130 is at about the frequency of the drive signals152,154 to maximize the efficiency of the power supply. In this embodiment, the drive signal frequency is about one megahertz, though other frequencies may be used.
• The drive signals152 and154 are supplied by acontroller150 such as a Unitrode UC3875QP or other similar product. Thecontroller150 receives the biasing power at pins28 and1 from the primarypower supply circuit160.
• Each of thecoils122 and132 induce a varying magnetic field in the outer legs of thecore20. Thesecondary coil212, which has acenter tap213, is coupled to a halfwave rectifier bridge214, which may comprise an MBRD66OCT, and then is coupled to afiltering circuit216 comprised of acapacitor218, aninductor220, andcapacitors222 and224 to provide a DC regulated output226.
• The regulation is provided by feeding back to the controller150 a signal modulated by a currentsensing amplifier circuit232 and avoltage sensing circuit240 comprising thefeedback circuit230. To provide the carrier for modulation, a furthersecondary carrier coil242 is coupled to one of the outer legs of thecore20. One of the legs of thistransformer coil242 is coupled to an isolation feedback transformer T2.
• The current sensing circuit takes the output of the center tap of thesecondary coil212 and provides a voltage drop across resistor R9 that is provided to currentsensing amplifier circuit232. The output of the currentsensing amplifier circuit232 is added to a voltage dropped across R13 and is provided to anamplifier244 in thevoltage sensing circuit240. The other input in the voltage sensing circuit is a reference voltage developed by theZener reference diode246 and also provided as a biasing level to the currentsensing amplifier circuit232. The output of theamplifier244 is provided to the base of bipolar transistor Q3, which may be a MMBT2907T, configured in a common base configuration, to amplitude modulate the current through thesecondary side coil246.
• Theprimary side coil156 of feedback transformer T2 is magnetically coupled to the secondary side coil of246 and generates an amplitude modulated signal that is envelope detected and integrated to provide a feedback voltage atinput22 of thecontroller150.
• As a result, as the amplitude of the envelope of the modulated signal increases, the voltage atinput22 of thecontroller150 increases. When thecontroller150 determines that the voltage has exceeded a predetermined limit, indicating that either the current or voltage at the output has increased beyond the predetermined maximum, the relative phase difference of driver signals152 and154 is increased. If the amplitude atinput22 decreases below a predetermined threshold indicating that the voltage or the current is below the desired levels, the relative phase ofsignals152 and154 is decreased towards zero to increase the voltage or current. Due to the summing effect of the magnetic flux atsecondary coil212, a highly efficient control or regulation of the power supply circuit is obtained.
• Because of the high efficiency that is attained with this circuit, heat dissipation is much less and it is possible to reduce the size of power supply to a much smaller form factor. In particular, each of the electrical components inFIG. 2, other than the transformer, may be mounted using surface mount devices on a printed circuit board. Further, each of the inductors and transformer cores are low profile or planar cores mounted through cutouts formed in the printed circuit board. The coils of the inductors and transformers are provided by wiring traces on the circuit board that wrap around the portion of the appropriate core penetrating the circuit board. As a result, an extremely compact form factor may be obtained.FIG. 4 shows a top planar view of such a printed circuit board with each inductor L1, L2 and transformer cores T1 and T2 identified.
• Notwithstanding the smaller size of the form factor, heat dissipation is not a serious problem due to the increased efficiency of the power supply according to the disclosed embodiments. Therefore, with all the components assembled on a printed circuit board as described above, the assembled printed circuit board may be housed within a housing formed from an injection molded plastic dimensioned 2.75×4.5×0.436 inches without undue heating of the housing, although other dimensions may be used with a key to maintaining a thin profile of the power supply being the ratio of the surface area of the top and bottom surfaces to the overall thickness of the housing. With proper heat sinks, for example, even smaller dimensions may be attained. For example, with such a housing, surface temperatures on the housing should not exceed one hundred twenty degrees Fahrenheit. A normal electrical plug such as a phased, three-prong plug, is coupled by an input cable (not shown) through a hole formed in the housing and an output cable (not shown) having a connector (not shown) coupled to the printed circuit board and to an output connector. Alternatively, the three-prong plug (not shown) may be formed within the housing with the prongs projecting from the housing to avoid the opening for a cable. Also, the plug may be of a pivotable type (not shown) mounted on the surface of the housing and rotate between a recessed position in a cutout formed within the housing and an in use position projecting at ninety degrees from the surface of the housing.
• Although the disclosed embodiment shows only one regulated DC voltage being supplied (for example +5 or +16 volts DC), it would readily be understood by those of ordinary skill in the field that other regulated or unregulated voltages may also be supplied with minor modifications to the disclosed embodiment. For unregulated voltages, additional secondary coils (not shown) with the appropriate number of windings to provide the voltage may be magnetically coupled to any of the legs of thetransformer core120. The appropriate circuitry must then be provided for rectifying and filtering the output of this additional secondary coil. Similarly, an additional regulated voltage may be supplied by providing a feedback control circuit such as the type described above that provides the appropriate feedback.
• FIG. 5A shows a top planar view of acase300 for an additional embodiment of the invention substantially having the shape of a right parallelepiped. The case may have dimensions of 5 inches long by 2.85 inches wide and the thickness (not shown) is 0.436 inches. Both the top portion of thecase300 and the bottom portion (not shown) define a number oflouvers304 definingmultiple openings302. The configuration of theopenings302 on both the top and bottom (not shown) portions of the cover are relatively unimportant. These openings must, however provide sufficient air circulation so that even when operating at maximum rated output power such as seventy-five watts DC, the surface temperature of thecase300 is less than one hundred and forty degrees Fahrenheit and preferably less than one hundred and twenty degrees Fahrenheit when the unit is operated at the maximum rated power of, for example seventy five watts DC. Having the openings defined on both the top and the bottom permits the user to operate the power supply in both the “right side up” and the “upside down” position with adequate air circulation. The case may be made of any high impact suitable plastics, such as Lexan or ABF, and when the top and bottom portions are assembled together such as by a snap lock or a force fit, they define a chamber in which all of the components are housed. Also, the exact dimensions are not critical, but preferably, the ratio of the top and bottom surface areas should be much greater than the thickness.
• FIG. 5B shows a partial cross-section of top portion of thecase300. In preferred embodiments of the present invention, athin layer306 of material is connected to the bottom of thelouvers302 to cover theopenings304 that lead into the interior of thecase300. Thethin layer306 is thin enough to still allow heat to pass through theopenings304 using ordinary convection. However, thethin layer306 is thick enough to prevent entry of liquids into thecase300, which could affect operation of the power supply. In preferred embodiments, the thin layer is 1 to 3 mils thick. However, in alternative embodiments, thinner or thicker layers may be used, so long as the layer is thick enough to resist penetration of liquids into thecase300 and as long as the layer is thin enough to permit normal heat dissipation by convection. In preferred embodiments, thethin layer306 is formed from a plastic material, such as Lexan, ABF or the like from which the remainder of the case is also formed. However, in alternative embodiments, thethin film306 may be formed from metals, composites, ceramics or other heat conductive and liquid resistant materials.
• In an assembled unit, immediately beneath the top (and above the bottom (not shown)) of thecase300 are heat sinks such as those shown inFIG. 6. Each heat sink, which comprises a thin sheet of thermally conductive material such as aluminum (which may be anodized) is configured preferably to fit precisely within the top or bottom portions of the case and defines a number of cutouts. These cutouts may provide clearance for certain components to be directly cooled by air entering through theopenings304 defined between thelouvers302 or may be provided for clearance of the components mounted on the printed circuit board (not shown). Preferably, whatever pattern of cutouts are formed in the heat sink, the pattern should be positioned so that when the unit is assembled, the heat sink material should provide adequate coverage over the openings in thecase300 to resist penetration of spilled liquids into the assembled unit. This allows the unit to comply with Underwriters Laboratories and other safety standards. Alternatively, the top and bottom heat sinks may cover the entire power supply circuit board (not shown). Of course, other suitable materials besides aluminum may be used for the heat sinks. In preferred embodiments of the present invention, the undersides of the louvers are scalloped (either along the length of thelouver302 or from side to side of the louver302) to provide an air gap between thelouvers302 and the heat sink to minimize conduction of the heat from the heat sink to the material of thecase300 andlouvers302.
• As shown inFIG. 5B, thelouvers302 are spaced close together to form theopenings304 so that theopenings304 have a relatively narrow width. The width and depth of theopenings304 are chosen so that fingers cannot come into contact with either thethin layer306 or the heat sinks under thethin layer306. This minimizes the heat transfer to the user so that the touch temperature of the unit appears lower than the actual temperature. In preferred embodiments, theopenings304 are 3 to 5 mm, which is narrow enough to prevent the entry of fingers from small children. However, in alternative embodiments, narrower orwider openings304 may be used, with the width being selected based upon the environment in which the power supply will be used.
• FIG. 5C illustrates a partial cross-section of another embodiment of the louvers in accordance with an embodiment of the present invention. In this embodiment, thelouvers310 are formed from a single piece of material with raisedridges312 separated bydepressions314. The depressions are connected and secured to the heat sink316 (such as those shown inFIG. 6) by adhesives, snap fit, simple contact or the like. The raisedridges312 of thelouvers310 are spaced close together to form thedepressions314 so that thedepressions314 have a relatively narrow width. The width and depth of thedepressions314 are chosen so that fingers cannot come into contact with either the bottom of thedepressions314 or theheat sink316. This minimizes the heat transfer to the user so that the touch temperature of the unit appears lower than the actual temperature. In preferred embodiments, thedepressions314 are 3 to 5 mm, which is narrow enough to prevent the entry of fingers from small children. However, in alternative embodiments, narrower orwider depressions314 may be used, with the width being selected based upon the environment in which the power supply will be used. To minimize the transfer of heat from the raisedridges312, anair gap318 is formed beneath anundersurface320 of the raisedridges312 and theheat sink316. Theair gap318 acts as an insulator so that the touch temperature of the case is lower than the actual temperature of the powersupply heat sink316. In preferred embodiments, the raisedridges312 and thedepressions314 are formed from a plastic material, such as Lexan, ABF or the like from which the remainder of the case is also formed. However, in alternative embodiments, the raisedridges312 and thedepressions314 may be formed from composites, ceramics or other heat conductive resistant and liquid resistant materials.
• FIGS. 7A and 7B show a schematic for thepower supply circuit800 with all resistance in ohms and all capacitance in microfarads unless otherwise labeled. The power supply is formed on a multilayer printed circuit board (not shown) having length and width dimensions that are only slightly smaller than the exterior of the case and fit as precisely as possible within the chamber of thecase300 sandwiched between the heat sinks to minimize movement after assembly. Further, as far as possible, surface mount devices are used to minimize the vertical dimension and all coil cores are preferably planar, low profile cores. Optimally, parts having the smallest possible thickness should be used.
• Thepower supply800 includes aninput circuit810 that may be coupled to any AC power source preferably having a frequency of between about 50 to 90 hertz and preferably having a voltage of between about 90 to 240 Volts AC. Thisinput circuit810 may include a fullwave bridge rectifier812, a filter circuit814 and aregulation circuit816 to provide an independent power supply for all integrated circuits used on theprimary side824 of the circuit. For filtering purposes, theinput regulator circuit816 may also include a center tappedcoil819 mounted on one of the exterior legs of the “E”planar core822 of the transformer820. (Preferably, the planar “E” core of the type shown inFIG. 2 is used.) When the AC input voltage exceeds a predetermined range such as one hundred and forty volts RMS, transistor Q9 in cooperation with Zener diode VR1 will cooperate so that the center tap of thecoil819 will be selected. This permits the output Vbias of the regulator to be in an acceptable range for higher input voltages such as may be common outside of the United States. The output Vbias is used for supplying power to all of the internal integrated circuits on theprimary side824 of the transformer820, namely integrated circuits U1 and U2. This permits these integrated circuits U1, U2 to continue functioning even if the DC output voltage from thepower supply800 drops below the range necessary for the integrated circuits U1 and U2 to continue operating.
• A controller integrated circuit U1 provides the four control signals for powering the MOSFETs coupled to the two primary coils825 and827 with their center taps coupled to Vbias. The outputs of integrated circuit U1 atpins7 through10 provide the control signals to a MOSFET driver circuit U2 such that MOSFETs Q1, Q2, Q4 and Q5 provide the appropriate phase control as is described in connection withFIG. 8. Integrated circuit U2 may be for example a 4468 available from Micrel, Teledyne and Telcom.
• Each of power switching MOSFET transistor pairs Q1 and Q2, and Q4 and Q5 are coupled to center tapped primary coils825 and827, respectively. These transistors preferably have heat sinks (not shown) coupled to their cases, and/or these heat sinks may also be thermally coupled to one of the heat sinks mounted immediately below and immediately above the top and bottom heat sinks for better thermal control. The capacitance of the MOSFETs Q1, Q2, Q4 and Q5 and the inductance of the coils825 and827 are selected to provide resonance at the frequency at which the drive signals are supplied, which may be about 1 MHz. Nonetheless, other frequencies may be used, for example, between a range of about 500 KHz to 2 MHz.
• FIG. 8 shows a timing diagram of the signals at nodes L through Q shown onFIGS. 7A and 7B. The integrated circuit U1, as described in more detail below, through feedback, provides MOSFET driving signals L through O. The MOSFET driving signals provided to each primary winding,825 and827 (i.e., L and M for primary winding825 and N and O for primary winding827) are always one hundred eighty degrees out of phase as shown inFIG. 8. However, the relative phase relationship of driving signal pair L and M for primary winding825 with respect to driving signal N and O for primary winding827 may be changed by the integrated circuit controller U1 in the manner described below to provided the regulated DC output voltage atconnectors846 and848. Maximum power is provided when the pairs of driving signals are in phase with each other. It should be noted that while the control signal provided atpins7 through10 are preferably at substantially a fifty percent duty cycle, the resistors R10 through R13 and the capacitors C10 through C13 combine with the integrated circuit U2 to provide preferably driving pulses L through O with a duty cycle of less than 50 percent. This ensures that the FETS in a pair (i.e., Q1 and Q2 for winding825 and Q4 and Q5 for winding827) are never both on at the same time to provide zero resonant switching and reduce power consumption.
• Due to the zero volt resonant switching design of the circuit, MOSFET pair Q1 and Q2 are preferably never on the same time and MOSFET pair Q4 and Q5 are preferably never on at the same time. MOSFET Q1 will turn on just about when the voltage at node P, which is at the drain of transistor Q1, reaches a minimum and will turn off immediately after the voltage at the drain of transistor Q1, goes above that minimum level. Similarly, due to the phase relationship of drive signal pair L and M at nodes L and M, transistor Q2 will only be on when the voltage at the drain is almost at the minimum. Transistor Q4 will also only be on when the voltage at node Q is virtually at its minimum and the transistor Q5 will only be on when the voltage at its drain is nearly at its minimum.
• It should be noted that the duty cycle of signals L through O is selected so that the waveforms P and Q are substantially trapezoidal with clipping occurring by transistors Q1, Q2, Q4 and Q5. This permits operation of the circuit over a wider range of input voltages. However, in alternative embodiments, transistors Q1, Q2, Q4 and Q5 need not clip so that the waveshapes at the drains of these transistors are substantially sinusoidal. Alternatively, using a low enough frequency for the drive signals, a square wave on the drains of the actual transistors could be used but would probably require larger cores.
• For thesecondary side826 of thepower supply circuit800, a single secondary winding840 is located at the magnetic summing node of the core822 (i.e., the center leg of the low profile “E” type core shown inFIG. 2). That secondary winding840 is coupled to arectifier circuit842 and then to an output filter844 including a filter choke L2 to provide the regulated DC output atconnectors846,848 in the manner described below.
• The center tap of the secondary winding842 is coupled through a coil in the filter coil L2 sharing a common core with the coil in the output filter844. Through resistor R23, this center tap of winding842 provides a current sense input to a summing amplifier U3A. A voltage sense of the output DC regulated voltage Vout is provided to an amplifier including amplifier U3C. The sensed voltage signal at the output of amplifier U3C is provided to the summing amplifier U3A through amplifier circuit U3B to provide the feedback necessary for the desired regulation of the DC output.
• The output of the summing amplifier U3A is provided through an emitter follower transistor Q7 to the center tap of thesecondary side826 of the feedback transformer850. This transformer is magnetically isolated from the transformer820. The signal at the center tap of transformer850 amplitude modulates a carrier signal provided by winding852 provided on the same exterior leg of the core822 as primary winding827. Preferably also, this should be the opposite exterior leg of thecore822 on whichcoil819 and winding825 are mounted.
• Theprimary side824 coil of transformer850 provides an amplitude modulated feedback signal that has an amplitude envelope. A diode detector comprised of diode CR5 and resistor R17 strip the carrier away, leaving the amplitude envelope as a feedback control signal to the VMOD input (pin1 of U1) to provide the feedback useful for altering of the phase relationship between the drive signal pairs of signals L and M on the one hand, and signals N and O, on the other hand to regulate the DC power supply output atconnectors846,848.
• With thecurrent control connector860 and thevoltage control connector862 left unconnected (as shown), amplifiers comprising U3B and U3D along with the current and voltage sense signals cause the integrated circuit U1 to control the phase relationship between the drive signal pairs L and M, on the one hand, and N and O, on the other hand, to provide a constant power supply until the output voltage drops below about ten volts. Then, due to the feedback signal atpin1 of the controller U1, the integrated circuit controller U1 controls the relative phase relationship between the pair of drive signals L and M, on the one hand, and N and O, on the other hand, to provide a constant current source down to a minimal voltage, which is preferably less than about one volt.
• It should also be noted that the Vcc used by the amplifiers U3A through U3D in the integrated circuit U3 and the voltage regulator U4 to generate the +5 volts used in the control circuit (e.g. comprising amplifiers U3B, U3C and U3D) is supplied by arectifier circuit854. Therectifier circuit854 is also coupled to secondary coil852.
• FIG. 9 shows a block diagram900 of the controller integrated circuit U1.Pins13,14, and15 cooperate together along with external components R3, R4, R5 and R6 to set the operational frequency of theoscillator902 to be preferably at 2 MHz, although other frequencies may be selected. An output of theoscillator902 is coupled to aninternal capacitor901 to provide a triangle signal labeled Ramp onFIGS. 10A and 10B while another output of theoscillator902 is a 2 MHz square wave coupled to exclusive ORgate904 and the clock input of aD flip flop907. ASchmitt trigger comparator906 compares the feedback signal VMOD atpin1 with the ramp signal as is shown inFIGS. 10A and 101B. InFIG. 10A, the VMOD signal, which is the envelope of the feedback signal from the feedback transformer850 is at the maximum level, while inFIG. 10B, the VMOD signal is somewhat less than the maximum. As can be seen inFIGS. 10A and 10B, thecomparator906 cooperates with theD flip flop907, the exclusive ORgate904, and the associatedlogic gates908 to generate one shot control signals J and K. As can be seen by comparingFIG. 10A, when VMOD is at a maximum, the one shot drive signals J and K are controlled so that both one shot control signals go high at the same time. When the amplitude of VMOD drops below the maximum, the timing of the one shot control signal J is retarded and the timing of the one shot control signal K is advanced. These one shot control signals J and K are provided to oneshot circuits920 and930 within the controller circuit U1, which have dual outputs VA and VC and VB and VD respectively. The oneshots920 and930 trigger on the rising edge of signals J and K respectively, and the durations to the falling edge of the control signals J and K are irrelevant provided that they fall before the one shots need to be retriggered. Due to the inclusion ofinverters922 and932, the output pair of signals VA and VC and VB and VD are approximately one hundred and eighty degrees out of phase. It should also be noted that the external capacitor C7 and resistor R7 are coupled topins5 and4 of the controller U1 to control the duration of the output pulses at the oneshot920 and the one shot930 to trigger them for the same duration. Further, these component values are selected to be as near as possible to provide a fifty percent duty cycle on the outputs L through O of the MOSFET driver circuit U2 at the frequency of operation.
• The controller circuit U1 also includes areference voltage generator940 that provides the reference voltage for the overvoltage protection circuit942 and thecomparator944. As shown inFIG. 7, an overvoltage protection circuit830 having acoil832 is located at or near the summing node of theE block core822. The value of the components within overvoltage protection circuit830 are selected such that if the output voltage DC Output goes above a predetermined threshold, silicon controlled rectifier (SCR) Q3 will fire, shunting the Vbias to ground. This will cause the integrated circuits U1 and U2 to cease operating, thereby shutting down the output until the unit is recycled by temporarily removing the AC input voltage.
• Thus, a small, highly efficient form factor power supply has been disclosed that may be readily mounted within a small container having a thickness of 0.436 inches or less and having dimensions suitable for holding in a typical shirt pocket or calculator pocket in a brief case at high power levels of up to about 75 watts DC output with a surface temperature of about 140 degrees Fahrenheit at the surface. Thicknesses of less than 0.436 inches may be attainable if thinner electrolytic or other types of filtering capacitors can be obtained using standard production techniques. Alternatively, a thinner case may be obtained by maximizing coupling of heat generating components to the heat sinks with maximum air flow through the openings defined by thelouvers302 and by making the top and bottom surface areas of the case larger. Regulation of the output voltage may be readily attained. Still further, the secondary coil can be positioned where the magnetic flux induced in the core from the two primary coils destructively interfere with each other and where the phase of the two driving signals is approximately one hundred eighty degrees out of phase at maximum output. In further alternatives, cooling methods other may be used, such as small electric fans, thermal-electric coolers or the like, to permit smaller form factor power supply configurations. Other alternatives will be readily apparent to those of skill in the art. It should be noted that in alternative embodiments, the various resistors, capacitors, frequencies and inductors may be different and other types of integrated circuits may also be used.
• FIGS. 12-16 illustrate animproved transformer core1010 in accordance with an embodiment of the present invention.FIG. 12A shows a top plan view of thetransformer core1010, which is formed by abase plate1012, asecondary leg1014 and a pair ofprimary legs1016 and1018. Thesecondary leg1014 and the primary legs of thetransformer1010 may be bosses attached to thebase plate1012 by welds, magnetically permeable adhesives, or the like, or the entire assembly may be molded using magnetically permeable powder.FIGS. 12B and 12C show two side plan views of how thetransformer legs1014,1016, and1018 are positioned on the base plate.FIG. 13A shows a top plan view of atransformer cap1020, which is secured to thelegs1014,1016, and1018 of thetransformer core1010 to complete the transformer core once the bosses have been inserted through cutouts. Thetransformer legs1014,1016, and1018 are secured to thetransformer cap1020 by magnetically permeable adhesives, welding or the like.FIGS. 13B and 13C show side plan views of thetransformer cap1020.
• In preferred embodiments, thetransformer core1010 andtransformer cap1020 are formed from a ferrite material. The operational frequency range of the core is from about 0.5 to 1.0 MHZ. Also, the initial magnetic permeability is preferably 1400±20%. In addition, the saturation flux density may be 5300 gauss, and the Curie temperature may be 250 degrees Centigrade. The core loss while operating at a frequency of 1 MHZ should preferably be approximately 500 KW/m at 500 gauss. In other embodiments, different core parameters may be used.
• In the disclosed embodiments, thebase plate1012 and the transformer cap are dimensioned to be 1.260×1.260×0.075 inches. Thesecondary transformer leg1014 is dimensioned to be 0.800×0.200 by 0.060 inches, and each primary transformer leg is 0.133×0.700×0.060 inches. Thesecondary transformer leg1014 is positioned away from theprimary transformer legs1016 and1018, as shown inFIGS. 12A-12C, to maximize the cross-sectional area of each of the transformer legs (i.e., the length and width of the transformer legs). This maximizes a ratio of the cross-sectional area of the transformer legs to the windings, thereby requiring less windings for the same magnetic coupling. Fewer windings means less area of a layer of a circuit board may be used so that the number of layers on the circuit board may be minimized. The improved transformer core also provides this maximized ratio while maintaining the ratio of the secondary to the primary windings at a constant value. However, in alternative embodiments, slightly different dimensions for the core parts may be used. Also, as described in the previous embodiments, the secondary coil is still positioned at a summing point of the primary coils.
• FIG. 14 shows a printedcircuit card layer1030 without secondary or primary cores attached and havingcutouts1014′,1016′ and1018′ to allow thecorresponding transformer legs1014,1016 and1018 to pass through the printed circuit board.FIG. 15 shows another printedcircuit card layer1030″ in which asecondary coil pattern1040 surrounding the cut-out1014′ for thesecondary transformer leg1014.FIG. 16 shows still another printedcircuit card layer1030′ in whichprimary coil patterns1042 and1044 surround the cut-outs1016′ and1018′ for the toprimary transformer legs1016 and1018, respectively.
• FIGS. 17-22 illustrate an alternative embodiment using twotransformer cores1110 in accordance with the present invention.FIG. 17A shows a top plan view of bottom portion of thetransformer core1110, which is formed by abase plate1112, acentral leg1114 and a pair ofperipheral legs1116 and1118. Thecentral leg1114 and the peripheral legs of thetransformer1110 may be bosses attached to thebase plate1112 by welds, magnetically permeable adhesives, or the like, or the entire assembly may be molded using magnetically permeable powder.FIGS. 17B and 17C show two side plan views of how thetransformer legs1114,1116, and1118 are positioned on thebase plate1112.FIG. 18A shows a top plan view of atransformer cap1120, which is secured to thelegs1114,1116, and1118 of thetransformer core1110 to complete the transformer core once the bosses have been inserted through cutouts. Thetransformer legs1114,1116, and1118 are secured to thetransformer cap1120 by magnetically permeable adhesives, welds or the like.FIGS. 18B and 18C show side plan views of thetransformer cap1120.
• In preferred embodiments, thetransformer core1110 andtransformer cap1120 are formed from a ferrite material that has properties and characteristics that are similar to those of the embodiment with thetransformer core1010, discussed-above.
• In the disclosed embodiments, thebase plate1112 and thetransformer cap1120 are dimensioned to be 1.113×1.113×0.075 inches. Thecentral transformer leg1114 is dimensioned to be 0.300×0.300 by 0.060 inches, and each peripheral transformer leg is 0.075×0.630×0.060 inches. Thecentral transformer leg1114 is positioned away from theperipheral transformer legs1116 and1118, as shown inFIGS. 17A-17C, to maximize the cross-sectional area of the central transformer leg1114 (i.e., the length and width of the central transformer leg). This maximizes a ratio of the cross-sectional area of thecentral transformer leg1114 to the windings, thereby requiring less windings for the same magnetic coupling. Fewer windings means less area of a layer of a circuit board may be used so that the number of layers on the circuit board may be minimized. The improved transformer core also provides this maximized ratio while maintaining the ratio of the secondary to the primary windings at a constant value. Also, as described in theprevious transformer core1010 embodiment, the secondary coil is still positioned at a summing point of the primary coils.
• FIG. 19 shows a printedcircuit card layer1130A defining asecondary coil1040′ and havingcutouts1114′,1116′ and1118′ andcutouts1114″,1116″ and1118″ to allow thecorresponding transformer legs1114,1116 and1118 of twotransformer cores1110 to pass through the printed circuit board. Thesecondary coil pattern1140′ passes around bothcentral leg cutouts1114′ and1114″ to magnetically couple thesecondary coil pattern1040′ with the summing point of two primary coils (seeFIGS. 20 and 21).FIG. 20 shows another layer1130B of the printed circuit card in which two primary coil patterns1142′ and1142″ surround the correspondingcentral cutout1114′ and1114″, respectively.FIG. 21 shows another printedcircuit card layer1130C in which two additionalprimary coil patterns1144′ and1144″ surround the correspondingcentral cutout1114′ and1114″, respectively. It should be noted thatprimary coil patterns1144′ and1144″ are coupled to corresponding primary coil patterns1142′ and1142″ to form the two primary coils that drive the secondary coil.FIG. 22 shows still another printed circuit card layer1130D in which asecondary coil pattern1140″ surrounds the corresponding central cut-out1114′ and1114″, respectively. It should be noted thatsecondary coil pattern1140′ is coupled to the correspondingsecondary coil pattern1140″ to form the secondary coil that is coupled to the primary coils. Finally, it should be pointed out that theancillary coil patterns1146 surrounding theperipheral legs1116′ and1116″ are provided to produce a signal useful for protecting the circuit from over voltage.
• The applicant has found that this characteristic power and current curve provides good charging of lithium ion, nickel metal hydride, nickel cadmium and other rechargeable batteries. Thus, the small form factor power supply is capable of supplying sufficient power to a personal computer or the like, even when the batteries are thoroughly discharged. The constant current at theoutput connectors846,848 can provide minimal voltages down to about less than one volt because the controller U1 can attain relative phase shifts between the drive signal pairs to between about one degree to one hundred eighty degrees (i.e., signal N lags signal L between about one degree to one hundred eighty degrees and signal O and lags signal M between about one degree and one hundred eighty degrees). Thus, as shown inFIG. 11, if one were to draw a power versus output current curve and an output voltage versus output current curve of such a power supply, the slope of the output voltage curve is relatively constant until the output current reaches approximately 2.0 amperes, then slopes down to 10 volts at which time the output current is essentially constant at approximately 3.6 amperes for voltages under 10 volts. The output power curve increases relatively linearly until the current level reaches approximately 2.2 amperes, at which time the output power curve tends to level off until the current reaches it maximum value of approximately 3.6 amperes. Therefore, the power supply is capable of providing constant current to the personal computer or the like, even if the battery is only capable of producing a fraction of a volt. This power curve is determined as a result of the selected amplifier configuration associated with integrated circuit U3, which may be an LM324 on thesecondary side826. The predetermined limit may be as high as 75 watts DC for a power supply having an upper and lower surface area within thecase300 of about 14 square inches and a thickness of about 0.436 inches or less so that the ratio of the top or bottom surface areas to the thickness is about 30:1.
• However, the circuit can readily be programmed to provide other power/current characteristics, such as the power characteristics for lap top computers, appliances, cellular or portable telephones, notebook computers, game systems or the like. This may be accomplished by coupling additional resistors to ground and/or +5 volts (generated by a voltage regulator U4) to the current control and voltage control inputs.FIG. 7B shows such an embodiment, with resistors R860 and R862 connected between Vref (produced by the voltage regulator U4) andcurrent control input860 andvoltage control input862, respectively. In embodiments of the invention, multiple resistors such as resistors R860 and R862 may be selectively connected between ground or a regulated voltage, such as the +5 volts produced by the voltage regulator U4 (as shown inFIG. 7C), and thecurrent control input860 orvoltage control input862. In the embodiment shown inFIG. 7C, a switch S1 may be used to select which one of the resistors R860a, R860band R860cis connected between the regulated voltage and a control input CI, which may be acurrent control input860 or avoltage control input862, in order to control the output voltage or output current of the power supply. The switch S1 may be a mechanical switch, a transistor switch, a logic gate or the like and may receive an input signal to control which of the resistors R860a, R860band R860cis selected.
• In embodiments of the invention, the power supply may be used to power a variety of electrical appliances with varying input voltage and input current requirements by attaching various connectors to interface with the output connection terminal of the power supply and the input connection terminal of the appliance. These connectors may have a common type of input interface adapted to mate with the output connection terminal of the power supply but differing types of output interfaces adapted to mate with the input terminals of particular appliances. At the same time, a resistor from among resistors R860a, R860band R860cmay be selected to provide a particular output voltage or output current required by a particular electrical appliance.
• In embodiments of the invention, a resistor indicator (e.g., a color or symbol element associated with the connection of a selected resistor) may correspond to a connector characteristic to ensure that the selected connector and selected resistor match a particular appliance to be powered. For example, where a particular type of cellular phone is to be powered, the connector corresponding to that type of phone may be colored blue. Text associated with the mechanical switch setting corresponding to the resistor to be connected for powering that type of phone may also be colored blue. The user may be instructed to match the color of the mechanical switch setting to the color of the connector fitting the appliance input connection terminal. Alternatively, the connector and switch setting may both be marked with a symbol associated with a cellular telephone, the connector may be marked with an indication of a corresponding switch setting (such as a switch position number), a light may be activated or changed in color when the selected connector and selected resistor match, or the like.
• In embodiments of the invention, resistors and/or a resistor-and-switch combination similar to the one shown inFIG. 7C may be incorporated into connectors that interface between the power supply and the electronic appliance as described hereinafter. As in embodiments in which a switch is included as part of the power conversion circuit, the switch may be mechanical or electronic (e.g., a transistor-based switch or logic gate). In embodiments in which an electronic switch is used, the resistor selection may be based upon an input signal received by the switch.
• Alternatively, as shown inFIG. 23, thecurrent control input860 and voltage control input862 (seeFIG. 7) can be coupled through acable882 to controlcircuits884 commonly contained within therechargeable batteries886 coupled to theDC output connectors846 and848. Thesecontrol circuits884 may containamplifiers888,resistors890, digital to analog converters or any other analog signal generator that may be coupled to the current andvoltage control inputs860,862 through thecable882 coupled to the battery terminals for charging. This would permit the controller in the battery programmatically to regulate the voltage and the current provided at the DC output to minimize recharging time based upon the known characteristics of the battery.
• Preferably, the programming of the small form factor power supply is carried out using either resistive programming or analog programming. However, in alternative embodiments, other programming methods may be employed, such as digital or microprocessor controlled programming (with or without resistance ladder networks), with the type of programming technique being dependent on the power requirements of the device.
• FIG. 24 is a schematic of a programming circuit in accordance with an embodiment of the present invention that is used to resistively program the power supply to produce between 0 and 16 volts, andFIG. 25 is a schematic of another programming circuit in accordance with an embodiment of the present invention that is used to resistively program the power supply to produce between 16 and 18 volts.FIG. 26 is an end view of a connector that mates with the small form factor power supply (shown inFIGS. 3 and 7) and is useable to program the small form factor power supply, as shown inFIGS. 24 and 25.
• As shown inFIGS. 24 and 25, the power supply may be programmed remotely to provide the required power at voltages between 0 to 18 volts using various external cables having built in resistances that program the power supply to output the required power level (i.e., voltage and current). This method allows the small form factor power supply to be programmed for any value of voltage and/or current by connecting a resistor from the voltage and/or current programming pins (e.g., pins1 and4) to ground (e.g., pin3) as shown inFIG. 24, or from the voltage programming pin (e.g., pin1) to VOUT (e.g., pin4) for voltages above 16 volts as shown inFIG. 25.
• To program the voltage between zero and 16 volts, as shown inFIG. 24, the following formula is used:$R=\frac{10\left(V_{\mathrm{OUT}}\right)}{16\left(V_{\mathrm{OUT}}\right)}$
• where R=the programming resistance betweenpins3 and4 (in Kohms); and where V_OUT=output voltage.
• To program the output voltage between 16 and 18 volts, as shown inFIG. 25, the following formula is used:$R=\frac{10(V_{\mathrm{OUT}})}{V_{\mathrm{OUT}}-16}$
  where R=the programming resistance betweenpin2 and4 (in Kohms); and
  where V_OUT=output voltage.
• To program the output current between 0 and 3.6 amps, as shown inFIGS. 24 and 25, the following formula is used:$R=\left(\frac{I_{\mathrm{OUT}}+4.133}{3.647-I_{\mathrm{OUT}}}\right)⨯7.823$
  where R=programming resistance between 1 and 3 (in Kohms); and
  where I_OUT=output current
• In another method, analog programming of the small form factor power supply is used. This method allows the small form factor power supply to be programmed for any value of voltage and/or current by providing an analog voltage signal from the respective programming pins and ground.
• To program the output voltage between 0 and 18 volts, the following formula is used:
  where$V_P=\frac{V_{\mathrm{OUT}}}{3.2}$
  V_P=programming voltage applied to pin4 with respect topin3; and
  where V_OUT=output voltage.
• To program the output current between 0 and 3.6 amps, the following formula is used:$I_P=\left(\frac{I_{\mathrm{OUT}}}{1.238}\right)+1.68$
  where I_P=programming voltage applied to pin1 with respect topin3; and
  where I_OUT=output current.
• In addition, the power supply may interface with a programmable current generator interface, such as an MC33340 fast charge battery controller manufactured by Motorola, Inc. of Schaumberg, Ill. or a BQ2002C manufacture by Benchmarq, Dallas, Tex. This allows the cable to directly interface with the power supply, while performing the functions of charge termination or trickle charging. In preferred embodiments, there is a ½ power factor available. The cable includes a chip that is adapted to work with a specific device, such as a cellular telephone, laptop computer or the like, so that the charging characteristics of the power supply are altered as needed by simply changing cables. Alternatively, a generic cable can be used and an adapter may be connected to the power supply between the cable and the power supply that contains different resistors that program the power supply to provide a desired power supply. Typically, precise charge termination is difficult to detect when the battery reaches saturation. Thus, preferred embodiments of the present invention detect the knee of the power curve shown inFIG. 11 and reduce the current to deliver at a more steady rate.
• FIGS.27(a)-34(c) show various cables with connectors in accordance with embodiments of the present invention that program the small form factor power supply for supplying power to different devices. These cables have aconnector1500 for connecting with the small form factor power supply and use various configurations of resistances and wire connections to program the small form factor power supply to work with various devices. In these figures, NC=no connection, +DC=V_OUT(e.g., frompin2 ofFIG. 26), CC=I_program(e.g., frompin1 ofFIG. 26), VC=V_program(e.g., frompin4 ofFIG. 26), and GND=ground (e.g., frompin3 ofFIG. 26). FIGS.27(a)-27(c) show views of acable1502 having aconnector1504 for use with IBM computers, such as the “ThinkPad” or the like. No resistances are provided in theconnectors1500 and1504, since the IBM computers provide their own power regulation, and the pins from the small form power supply (e.g.,FIG. 27(c)) are converted to a compatible connector and pin out, as shown inFIG. 27(b). FIGS.28(a)-28(c) show views of acable1506 having aconnector1508 for use with IBM computers, such as the “ThinkPad” or the like, and for Compaq computers, such as the Armada or the like. No resistances are provided in theconnectors1500 and1508, since the IBM and Compaq computers provide their own power regulation, and the pins from the small form power supply (e.g.,FIG. 28(c)) are converted to a compatible connector and pin out, as shown inFIG. 27(b). FIGS.29(a)-29(c) show views of acable1510 having aconnector1512 for use with for Compaq computers, such as the Contura, LTE or the like, Toshiba computers, such as the Satellite and the Protege, Gateway computers, such as the Solo, and Hitachi computers, such as the C120T and the like. Either theconnector1500 or theconnector1512 use resistances betweenpins2 and4 of the small form factor power supply to program the small form factor power supply. FIGS.30(a)-30(b) show views of acable1514 that does not have a connector. Theend1516 of thecable1514 is left with bear wires to be configured to work with various computers that don't use the resistances or connectors shown in the other cables. Since thecable1514 has no end connector, it can be wired to match various computer configurations. FIGS.31(a)-31(c) show views of acable1518 having aconnector1520 for use with another configuration of a computer. Either theconnector1500 or theconnector1520 use resistances betweenpins1,3 and4 of the small form factor power supply to program the small form factor power supply. FIGS.32(a)-32(c) show views of acable1522 having aconnector1524 for use with Hewlett Packard computers, such as the Omnibook or the like. Either theconnector1500 or theconnector1524 use resistances betweenpins3 and4 of the small form factor power supply to program the small form factor power supply. FIGS.33(a)-33(c) show views of acable1526 having aconnector1528 for use with Toshiba computers, such as the Tecra or the like. Either theconnector1500 or theconnector1528 use resistances (having a different value than those for cable1522) betweenpins3 and4 of the small form factor power supply to program the small form factor power supply. FIGS.34(a)-34(c) show views of acable1530 having aconnector1532 that is designed to be a universal cable that accepts various connector ends that can mate with different device. No resistances are provided in theconnectors1500 and1532, since thecable1530 is converted to be compatible with various devices based on the connector adapters connected to theconnector1532.
• FIGS.35(a)-40(c) show various connector adapters for use with thefemale connector1532 of thecable1530 shown above in FIGS.34(a)-34(c). FIGS.35(a)-35(c) show aconnector adapter1534 having amale connector1536 for connecting with theconnector1532 and has anend connector1538 that converts thegeneric cable1530 of FIGS.34(a)-34(c) to correspond to thecable1502 shown in FIGS.27(a)-27(c). FIGS.36(a)-36(c) show aconnector adapter1540 havingconnectors1536 and1542 that convert thegeneric cable1530 of FIGS.34(a)-34(c) to correspond to thecable1506 shown in FIGS.28(a)-28(c). FIGS.37(a)-37(c) show aconnector1544 havingconnectors1536 and1546 that convert thegeneric cable1530 of FIGS.34(a)-34(c) to correspond to thecable1510 shown in FIGS.29(a)-29(c). FIGS.38(a)-38(c) show aconnector adapter1548 havingconnectors1536 and15505 that convert thegeneric cable1530 of FIGS.34(a)-34(c) to correspond to thecable1518 shown in FIGS.31(a)-31(c). FIGS.39(a)-39(c) show aconnector adapter1552 havingconnectors1536 and1554 that convert thegeneric cable1530 of FIGS.34(a)-34(c) to correspond to thecable1522 shown in FIGS.32(a)-32(c). FIGS.40(a)-40(c) show a connector adapter1556 havingconnectors1536 and1558 that convert thegeneric cable1530 of FIGS.34(a)-34(c) to correspond to thecable1526 shown in FIGS.33(a)-33(c).
• FIGS.41(a) and41(b) illustrate a block diagram and a schematic of an interface for providing power to more than one device at a time. As shown inFIG. 41(a), a small formfactor power supply2000 is connected through acable2002 to aninterface2004 that supports more than one device at a time by the power supply. Theinterface2004 can support two or more devices, with the number of devices being dependent on the number of power output ports. The power to each device is controlled by cable connections to each device, such as the cables and connectors described above in FIGS.27(a)-40(c). As shown inFIG. 41(b), theinterface2004 receives thecable2002, which has afirst voltage wire2006 providing a first voltage V1 and asecond voltage wire2008 providing ground G. This is generally connected to the primary device. Additional devices are connected towires2006 and2008 throughtaps2010 and2012.Tap2012, if necessary, feeds into a voltage regulator to change the voltage to that desired by the device and outputs a second voltage onwire2014 and ground onwire2016. In alternative embodiments, the additional regulator may be provided in the cable used for each device.
• FIGS. 42-44 show various perspective views of a small formfactor power supply3000 that has been configured for use with portable telephone equipment in accordance with an embodiment of the present invention (note: these drawings are from 3-Dimensional CAD drawings and the many lines in the drawings indicate curves on the small form factor power supply and do not represent surface features).FIGS. 45 and 46 show perspective views of the small formfactor power supply3000 connected to a cellular telephone battery and telephone. The small formfactor power supply3000 is directed to charging portable telephone batteries. It has ahousing3002 similar to that described above and uses the charging circuitry described above. However, in alternative embodiments, different charging topologies may be used, depending on the charging environment, the battery type and the weight requirements of the small form factor power supply. Embodiments of the small form factor power supply can be adapted to work with telephones manufactured by Audiovox, Ericsson/GE, Fujitsu, JRC, Mitsubishi/Daimondtel, Motorola, Murata, NEC, Nokia, Novatel, Oki, Panasonic, Sony, Uniden, AT&T, Tandy, Pioneer, JVC or the like. Also, the small form factor power supply can be used with a wide variety of portable telephone equipment, such as cordless telephones, cellular telephones, radio telephones, PCS telephones and the like.
• Thehousing3002 of the small formfactor power supply3000 includes afoldable AC plug3004 that is adapted to plug into a standard electrical socket (not shown) to receive power, from standard lines, that is to be transformed and supplied to an attached device. Alternative embodiments may use different plugs to handle different voltages and/or different country's electrical socket and power configurations. As shown inFIG. 42, theAC plug3004 folds into arecess3006 when not being used. TheAC plug3004 is unfolded by engaging and rotating atab3008 to rotate theAC plug3004 out of therecess3006. In alternative embodiments, the AC plug may be spring loaded and utilize a catch to lock the AC plug in the folded down position and once the catch is released the spring rotates the AC plug into the unfolded position. TheAC plug3004 may include detentes or use other methods to maintain theAC plug3004 in the folded or unfolded position. Once unfolded, theAC plug3004 can be inserted into the socket, and thehousing3002 generally hangs down against a wall for stability and support. In alternative embodiments, the AC electric plug may be recessed and fixed in the housing of the small formfactor power supply3000 to receive an electrical cord that is attached between the AC plug and an electric socket.
• As shown inFIGS. 42 and 43, apower output3010 is adapted to fold out and includes a plurality ofcontacts3012 that mate with the corresponding contacts (not shown) on a portable telephone equipment battery3011. In preferred embodiments, thecontacts3012 of the small formfactor power supply3000 are placed in electrical contact with the contacts on the back of the battery3011. Alternatively, when the battery3011 is not coupled to portable telephone equipment, thecontacts3012 of the small form factor power supply may be placed in electrical contact with the contacts of the battery3011 that provide power to the portable telephone equipment. To unfold thepower output3010, the user pushes thepower output3010 through aport3014 to force thepower output3010 to rotate down about ahinge3016. Thepower output3010 may be spring loaded with a catch, detentes or other methods to lock thepower output3010 in the folded or unfolded position. In alternative embodiments, the small formfactor power supply3000 may use a recessed connector that connects to either the portable telephone equipment or battery using a cable such as described above and below.
• The small formfactor power supply3000 also hassupport legs3018 that include ends withguide tabs3020. Theguide tabs3020 are shaped to engage withchannels3021 on the portable telephone equipment battery3011 to hold the battery3011 in electrical contact with the small formfactor power supply3000 during charging. Thesupport legs3018 are also capable of holding a portable telephone connected to the battery3011, as shown inFIGS. 45 and 46. Thesupport legs3018 are rotated out when the small formfactor power supply3000 is to be connected to a battery3011. To attach the small formfactor power supply3000, as shown inFIGS. 45 and 46, the user slides the battery3011 to engage thechannels3021 of the battery3011 with theguide tabs3020 of thesupport legs3018. The user then slides the battery3011 back, until it is stopped and contacts thepower output3010. In preferred embodiments, each of thesupport legs3018 rotates independently of the other to simplify manufacturing and reduce complexity of the small formfactor power supply300. However, in alternative embodiments, thesupport legs3018 may rotate out together as a unit and/or rotate out when thepower output3010 is rotated.
• In preferred embodiments, the small formfactor power supply3000 is capable of charging most telephone equipment batteries in less than 15 minutes. However, the actual charging time will vary based on the size of the battery and the battery chemistry. Most batteries (providing between 1 to 15 hours of high power operation) charge in 5-30 minutes. The small formfactor power supply3000 includes a temperature sensor that is included in the small form factor power supply control chip to charge the battery as described above. This temperature sensor allows the small form factor power supply to determine the proper charging rate for a battery and avoid generating undue heat by overcharging or charging at too high a rate. In further embodiments, the small form factor power supply can be used to power the portable telephone equipment simultaneously with charging of an attached battery. Alternatively, the small form factor power supply may be able to power the portable telephone.
• In the embodiment ofFIGS. 42-46, theAC plug3004, thepower output3010, and thesupport legs3018 are all designed to be folded in when the small formfactor power supply3000 is not in use. This minimizes the profile of the small form factor power supply when it is not in use and makes it easier to transport. In alternative embodiments, the AC plug, the power output and the support legs may be formed or maintained in the unfolded position, where the smaller profile is not needed or an advantage.
• FIG. 47-50 show a perspective and plan views of a small form factor powersupply adapter connector4000 for use with portable telephone equipment in accordance with embodiments of the present invention (note: these drawings are from 3-Dimensional CAD drawings and the many lines in the drawings indicate curves on the small form factor power supply and do not represent surface features). Theadapter connector4000 has ahousing4001 that includes aconnector4002 configured to mate with theconnector1532 ofcable1530 shown in FIGS.34(a)-34(c). This adapter connector provides an upgrade path for users that already posses a small form factor power supply, as described above.
• As shown inFIGS. 47-50, theadapter connector4000 includes a plurality ofcontacts4006 for connecting with corresponding contacts (not shown) on a portable telephone equipment battery. Thehousing4001 may also contain additional circuitry or electronics needed to properly program a small form factor power supply to charge a portable telephone equipment battery.
• Theadapter connector4000 includes leg supports4008 withguide tabs4010 that engage with channels on a battery (similar to those shown inFIGS. 45 and 46 above). To secure theadapter connector4000 to a battery, an end clip (not shown) attached to theadapter connector4000 by elastic straps (not shown), or the like. The elastic straps are threaded througheyelets4011 so that theadapter connector4000 can not slip off the battery. In the illustrated embodiment, the leg supports4008 are foldable about ahinge4012 to reduce the profile of theadapter connector4000 when not in use and/or when being transported. In alternative embodiments, thesupport legs4008 may be formed in a fixed open position.
• The small form factor power supplies described above are capable of charging various different types of batteries, such as NiCad and NiH. However, in alternative embodiments, the small form factor power supplies may charge batteries using Zinc air, Lead acid, alkaline or the like. The power supply may also be used to charge Lithium ion batteries, although a different control chip or circuitry may be required to handle the unique charging requirements of these batteries.
• While embodiments of the present invention are directed to a form factor power supply in particular, other embodiments of the present invention are directed more generally to power supplies which are programmable to provide power to any one of a number of electronic devices having differing input power requirements. The embodiment discussed above with reference toFIGS. 7A and 7B includes a power supply which is programmable to provide a power output at a terminal846 at a suitable operational current or operational voltage associated with the particular electronic device which is to be powered. The appropriate programming signal can then be applied to either terminal860 or862 using, for example, an appropriate connector associated with the device to receive power as discussed above with reference toFIGS. 23 through 41.
• FIG. 51 illustrates a schematic of an alternative embodiment of a programmable power supply5000 which receives input power from a DC power source and controls the output power using a pulse width modulation technique. Resistances are expressed in ohms and capacitances are expressed in micro farads unless noted otherwise. A DC input source such as a 12 volt automobile cigarette lighter is provided across terminals5011 and5012. Other embodiments may be adapted to receive power from other DC sources such as, for example, a DC power source in the passenger compartment of an airplane at different voltages such as 15 volts. The input circuitry of the embodiment shown inFIG. 51 differs from the embodiment shown inFIGS. 7A and 7B by, among other things, replacing the input transformer and full bridge rectifier circuit with a single inductor L21 in a Buck regulator topology.
• A transformer T21 includes aprimary coil5002 and asecondary coil5004. Theprimary coil5002 receives current from the inductor L21. This current through theprimary coil5002 induces an output current through thesecondary coil5004 to anoutput terminal5864. A switch transistor Q61 controls the current through theprimary coil5002 to affect the output current induced in thesecondary coil5004. An integrated circuit U21 opens and closes the switch transistor Q61 to pulse width modulate the current through theprimary coil5002. The integrated circuit U21 may be an integrated circuit number UC3845 sold by Unitrode. The integrated circuit U21 is preferably configured to provide fixed width pulses at anoutput pin6 during which the switch transistor Q61 is closed to provide a pulse of current through theprimary coil5002. The integrated circuit U21 then receives an input signal at aterminal2 to control the duty cycle of the pulse signal provided at theoutput pin6. Accordingly, by increasing or decreasing the duty cycle of the pulse signal provided at theoutput pin6, the output current induced in the secondary winding5004 may be increased or decreased to maintain the output power at terminal5864 at an appropriate operational voltage or current level. The output current of thesecondary coil5004 is then smoothed by capacitors C161 and C201 to provide a DC power output to theoutput terminal5864.
• Terminals5848,5860,5862 and5864 are preferably provided to a connector coupling the power supply5000 to the electronic device to be powered. In a manner similar to the embodiment discussed above with reference toFIGS. 7A and 7B, the terminal5860 provides a current control input and the terminal5862 provides a voltage control input. Connectors, such as those discussed above with reference toFIGS. 23 through 41, may then provide a programming signal to thecurrent control input5860 or thevoltage control input5862. In response to these inputs, a voltage is applied to aterminal2 of the integrated circuit U21 to control the duty cycle of the pulse signal output transmitted atoutput pin6. The current through thesecondary coil5004 is therefore controlled to provide an operational voltage or operational current at thepower output pin5864.
• While the embodiment shown atFIG. 1 is configured to receive a DC power input, this embodiment could be modified to accept an AC power input by, for example, replacing the input circuit having the inductor L21 with an input transformer followed by a full bridge rectifier as illustrated inFIGS. 7A and 7B. Also, the aforementioned small form factor design illustrated with reference toFIGS. 7A through 41 may be modified to accept a DC input by, for example, replacing the input transformer and full bridge rectifier circuit with a single inductor as shown in the embodiment ofFIG. 51.
• While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.
• The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims (27)

1. A small form factor power supply, comprising:

a low profile transformer for the power supply, the low profile transformer including:

a transformer core formed of a ferrite material,

primary coil windings on a first layer of a printed circuit board, the primary coil windings surrounding a first part of the transformer core, and

secondary coil windings on a second layer of the printed circuit board, the secondary coil windings surrounding a second part of the transformer core; and

a rectifier to receive a voltage from the secondary coil windings and to rectify the voltage to generate a rectified voltage.

2. The small form factor power supply ofclaim 1, further including additional secondary coil windings on the second layer of the printed circuit board, the additional secondary coil windings surrounding a third part of the transformer core.

3. The small form factor power supply ofclaim 1, wherein the first layer of the circuit board is located below the second layer of the circuit board.

4. The small form factor power supply ofclaim 1, wherein the first part of the transformer core is disposed in a first cutout of the printed circuit board.

5. The low profile transformer ofclaim 4, wherein the second part of the transformer core is disposed in a second cutout of the printed circuit board.

6. The low profile transformer ofclaim 1, wherein the first part of the transformer core is spaced apart from the second part of the transformer core.

7. A small form factor power supply, comprising:

a transformer for the power supply, the transformer including:

a transformer core made of a ferrite material, the transformer core including a first leg and a second leg; and

primary coil windings surrounding the first leg of the transformer core, the primary coil windings being located on a first printed circuit board layer;

secondary coil windings surrounding the secondary leg of the transformer core, the secondary coil windings being located on a second printed circuit board layer, wherein the second printed circuit board layer is above the first printed circuit board layer; and

a rectifier to receive a voltage from the secondary coil windings and to rectify the voltage to generate a rectified voltage.

8. The small form factor power supply ofclaim 7, the transformer core further including a base plate, the base plate being attached to the first leg and the second leg of the transformer core.

9. The small form factor power supply ofclaim 8, the first leg being disposed in a position parallel to a first edge of the base plate and the second leg being disposed in a position perpendicular to a second edge of the base plate, wherein the first edge is on an opposite side of the base plate from the second edge.

10. The small form factor power supply ofclaim 7, wherein the first leg of the transformer core is located in a first cutout of the first printed circuit board layer.

11. The small form factor power supply ofclaim 10, wherein the second leg of the transformer core is located in a second cutout of the second printed circuit board layer.

12. A small form factor power supply, comprising:

a transformer, the transformer including,

a transformer core made of ferrite material;

first secondary coil windings disposed on a first printed circuit board layer, the first secondary coil windings surrounding a first part of the transformer core;

primary coil windings disposed on a second printed circuit board layer, the primary coil windings surrounding a second part of the transformer core; and

second secondary coil windings disposed on a third printed circuit board layer, the second secondary coil windings surrounding a third part of the transformer core; and

a rectifier to receive a voltage from the first secondary coil windings and the second secondary coil windings to rectify the voltage to generate a rectified voltage.

13. The small form factor power supply ofclaim 12, wherein the primary coil windings are is located in between the first secondary coil windings and the second secondary coil windings.

14. The small form factor power supply ofclaim 12, wherein the second printed circuit board layer is located below the first printed circuit board layer.

15. The small form factor power supply ofclaim 12, wherein the second printed circuit board layer is located between the first printed circuit board layer and the third printed circuit board layer.

16. A small form factor power supply, the power supply including:

a low profile transformer, the low profile transformer including:

a transformer core made of ferrite material,

primary coil windings disposed on a first printed circuit board layer, the primary coil windings surrounding a first leg of the transformer core,

first secondary coil windings disposed on a second printed circuit board layer, the first secondary coil windings surrounding a second leg of the transformer core, and

second secondary coil windings disposed on a third printed circuit board layer, the second secondary coil windings surrounding a third leg of the transformer core; and

a rectifier to receive a voltage from the first secondary coil windings and the second secondary coil windings to rectify the voltage to generate a rectified voltage.

17. The small form factor power supply ofclaim 16, further including a base plate to which the first leg, the second leg, and the third leg are attached, wherein the second leg and the third leg are attached to the base plate on opposite edges of the base plate.

18. The small form factor power supply ofclaim 16, wherein the first leg is attached to the base plate in between the second leg and the third leg.

19. A small form factor power supply, comprising:

a low profile transformer, the low profile transformer including

a core, the core including a base plate, a first leg made of ferrite material attached to the base plate, and a second leg made of ferrite material attached to the base plate,

primary windings which surround the first leg of the ferrite material, and

secondary windings which surround the second leg of the ferrite material; and

a rectifier to receive a voltage from the secondary windings to rectify the voltage to generate a rectified voltage.

20. The small form factor power supply ofclaim 19, wherein the primary windings horizontally surround the first leg of the ferrite material.

21. The small form factor power supply ofclaim 20, wherein the secondary windings horizontally surround the second leg of the ferrite material and the primary windings and secondary windings lie in parallel planes with respect to each other.

22. The small form factor power supply ofclaim 20, further including a third leg of made of ferrite material attached to the base plate as part of the core and additional secondary windings which surround the third leg made of ferrite material.

23. The small form factor power supply ofclaim 22, wherein the primary windings horizontally surround the first leg of ferrite material, the secondary windings horizontally surround the second leg of ferrite material, and the additional secondary windings horizontally surround the third leg of ferrite material.

24. The small form factor power supply ofclaim 22, wherein the primary windings, the secondary windings, and the additional secondary windings lie in parallel planes with respect to each other.

25. The small form factor power supply ofclaim 22, further including a fourth leg made of ferrite material attached to the base plate as part of the core and additional primary windings which surround the first leg of the ferrite material, wherein the primary windings, the additional primary windings, the secondary windings, and the additional secondary windings lie in parallel planes with respect to each other.

26. The small form factor power supply ofclaim 25, wherein the primary windings are located in a plane below a plane in which the secondary windings are located.

27. The small form factor power supply ofclaim 26, wherein the primary windings and the additional primary windings are located in planes beneath planes in which the secondary windings and the additional secondary windings are located.

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