US20080144341A1 - Power converter - Google Patents

Abstract

A switch-type power converter includes a double FET switch operating in a variable duty cycle mode under the control of a Unitrode 3846 integrated circuit controller. Indications of excess input voltage and reverse battery connections are provided by circuits including an element which permanently changes state. A cooling fan mounted on a finned heat sink is operated in a variable speed mode.

Description

RELATED APPLICATION
• This application is a divisional of U.S. application Ser. No. 11/221,962 filed under attorney docket no. PDY-112-A on Sep. 8, 2005, currently pending. The content of the U.S. patent Ser. No. 11/221,962 is incorporated herein by reference.
FIELD OF THE INVENTION
• This invention relates to power converters, and more particularly to switch-type power converters designed for use in recreational vehicles as a regulated power supply for DC load devices and as a battery charger.
BACKGROUND OF THE INVENTION
• As used herein, the terms “recreational vehicle” and “RV” should be construed to embrace motor homes, trailers, campers, van conversions, fifth wheels, boats, and similar products. The common characteristic of these recreational vehicles is an electrical system incorporating one or more batteries to provide power for DC load devices, such as lights, refrigerators and motors. The more sophisticated recreational vehicles may also have alternating current systems and AC load devices such as stoves, televisions, microwaves and heating and ventilating systems. The AC load devices are typically powered, from, a 115 volt AC line voltage source brought to the recreational vehicle through a power cord and plug. Some recreational vehicles also carry generators powered by gas or diesel engines and capable of producing as much as 20 or more kilowatts of AC power.
• It has become common to install power converters in recreational vehicles. A typical power converter converts 115 vac to 13.6 vdc and charges the RV battery or batteries as necessary. It has become more and more common to use “switch type” power converters rather than linear converters. There are numerous reasons for this including a substantial weight savings. Switch type power converters, often simply called “switchers” or “switching” power converters, typically use one or two power switching semi-conductor devices such as field effect transistors (“FET's”) and a controller such as the Unitrode, UC 3846 for operating the semi-conductor devices in a variable duty cycle mode. Such devices further typically include a step-down transformer and a smoothing circuit between the transformer and the regulated output voltage terminal.
• A designer of such converters faces numerous issues including heat dissipation, noise generation, tolerance to unstable or excessive supply voltages and protection of the expensive circuit components found therein. The manufacturer of such devices faces these and other issues including warranty claims based on alleged defects when, in fact, field failures are often caused by improper use such as (1) accidentally connecting the converter input to an excessive voltage source such as a 220 vac line or an improperly regulated or runaway generator; and (2) accidentally connecting the RV battery in reverse polarity
• Power converters which deal with some of these issues are described in U.S. Pat. Nos. 5,600,550 and 5,687,066 issued to James Cook in February and November, respectively, of 1997 and assigned to Progressive Dynamics, Inc. of Marshall, Mich. The power converter described in the '550 patent is of the switch type in which the switch includes two FET's operating in a push/pull fashion under the control of an integrated circuit controller such as the Unitrode UC 3846. The converter further comprises a fan powered by the converter output and a pair of thermistors mounted on a large heat sink along with the FET's. One of the thermistors is used in combination with a set-point device to turn the fan on and off and the other is used to shut the controller down in the event temperature reaches an extreme or intolerable level.
• U.S. Pat. No. 5,687,066 describes a converter identical to that of the '550 patent but adds overvoltage protection. This feature is provided by a Zener diode to sense an overvoltage condition in the dc output of a diode rectifier bridge used to convert an ac line voltage to dc. If the rectified supply voltage exceeds a predetermined limit, the Zener diode conducts and quickly sends a signal to a shut down pin of the Unitrode controller to prevent the controller from turning the FET's on. This protects the FET's from damage until the overvoltage condition subsides.
SUMMARY OF THE INVENTION
• The subject invention has for its foundation a switch-type power converter/battery charger including a switch consisting of one or more FET's operating in a variable duty cycle mode. An integrated circuit controller such as the Unitrode UC 3846 is used with appropriate feedback and a rectifier and LC filter in the output stage to operate the switch to produce a regulated dc output.
• The subject converter in a typical commercial embodiment includes a rectifier bridge so that the unit may be connected to a standard 60 cycle normal 115 volt ac line. This is typical of the line voltage made available by electric utility companies and/or commercial generators. The feedback system is used to cause the overall converter to operate in a current demand mode wherein the duty cycle of the switch is adjusted to maintain the desired output voltage.
• In the preferred embodiment described herein, the converter further comprises a transformer for stepping voltages within the converter circuit down to a level suitable for use in connection with dc load devices and the charging of conventional storage batteries. Most of the reference voltages in the converter are taken from the primary side of the transformer. In addition, the fan supply and fan control are on the primary side of the transformer. By supplying the fan from the primary side, an undesirable drop in fan speed under heavy load conditions is avoided.
• According to a first, more specific aspect of the present invention, a circuit is provided at or near the dc input of the converter i.e., at or near the output of the ac-to-dc rectifier circuit, for providing a permanent indication of an abnormal over-voltage condition sufficient to cause circuit damage and likely to be the result of operator error. In general, the permanent over-voltage indicator comprises a circuit connected between the output of the ac-to-dc rectifier and ground and includes a device, such as a Zener diode, for establishing a very high breakdown voltage, and a device, such as a fuse, which permanently changes state in response to an over-current condition. The fuse and Zener diode are preferably chosen in the commercial embodiment to correspond to the conditions which might exist if the converter were accidentally connected to a 220 volt ac supply or to an unregulated or runaway generator. The permanent change of state in itself has no effect on converter operation, since it is not a shut down mechanism similar to that of the over-voltage protection feature. But it does provide the manufacturer or warrantor of the system with evidence that any damage occurring to the converter and/or its various circuit components was the result of an extreme over-voltage condition rather than system malfunction or component defects.
• The permanent input over-voltage indicator is preferably used in combination with an over-voltage shutdown circuit also connected to the output of the ac-to-dc rectifier. The location and overall purpose of the over-voltage shutdown circuit is generally as described in the '066 patent where it is referred to as an overvoltage “protection” circuit, but preferably uses an operational amplifier to establish the shutdown set point voltage in a way which is more precise than that available from the use of a Zener diode as described in the '066 patent. The output of the over-voltage shutdown circuit is connected to a shut down pin in the variable duty cycle controller so as to prevent the switch transistors from turning on (and off again) while the over-voltage condition persists. This protects the expensive FET's and other components in the switch from damage. The set point of the over-voltage shutdown circuit in the illustrated embodiment is lower than that associated with the permanent, over-voltage indicator device described above and the two circuits work in a cooperative fashion; i.e., the over-voltage shutdown circuit effects a shut down function at a first over voltage level whereas the permanent over-voltage indicator circuit changes state at a substantially higher over-voltage level likely resulting from, for example, owner/user error or generator runaway. However, the trip point of the overvoltage indicator could be set below or equal to the overvoltage shutdown circuit if the circuit designer wishes to do so.
• Another aspect of the present invention in the foundation environment described above is a permanent reverse battery connection indicator circuit. This circuit detects a so-called “reverse” battery condition which results from the erroneous reverse polarity connection of the storage battery to the recreational vehicle electrical system after a period of disconnection for storage or service. Like the over-voltage indicator, the permanent reverse battery connection circuit includes a component which undergoes a permanent change of state when the battery is accidentally connected with the positive and negative terminals in reverse positions. Again, the permanent indicator does nothing to shut down or disable system operation, but simply provides an unequivocal indicator of owner/user error in the event a warranty claim is later made.
• The converter of the present invention, like the converter described in the '066 patent, uses a metal heat sink as part of the converter packaging structure and mounts certain components on or in contact with the heat sink. A thermistor sensor, preferably mounted on or in contact with the heat sink, is used to monitor converter temperature and provide an output signal which; also unlike the '066 patent converter, is simultaneously supplied to two control circuits. The first control circuit operates the fan in a variable speed mode. These modes of operation are believed to not only extend fan life, but also reduce an annoying quality of fan noise. The thermistor sensor also furnishes a temperature-related signal to a second circuit including a comparator or “op-amp” to shut down the variable duty cycle controller in the event of a high temperature condition which may exceed the capacity of the fan.
• Other aspects of the invention in the area of thermal control include a special mounting arrangement between the fan motor and the extrusion which provides the heat sink; i.e., a recess is machined into an end of the heat sink extrusion to provide an air gap between the extrusion and the fan motor so that the fan motor does not directly pick up heat from the extrusion. In addition, heavy wire leads are used in overlying relationship to the copper plating of a circuit board used to mount the elements of the circuit ofFIG. 2. The wire leads are soldered to the board in high current connector areas. Numerous advantages flow from these packaging modifications as will be hereinafter explained in greater detail.
• Still further aspects and advantages of the invention are described herein and will be best understood from a reading of the following specification which describes and illustrative embodiment in the form of an 80 amp power converter for use in recreational vehicles of the type using conventional storage batteries.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a block diagram of a switched power converter circuit according to the present invention;
• FIG. 2 is a schematic circuit diagram of an illustrative switched power converter circuit embodying the inventive features described above;
• FIG. 3 is a graph of temperature versus fan speed illustrating the operating curve of the fan according to the present invention;
• FIG. 4 is a graph of fan voltage versus fan speed for a typical fan;
• FIG. 5 shows various waveforms within the circuit ofFIG. 17;
• FIG. 6 is a graph of output converter current versus temperature for a variety of fan speeds;
• FIG. 7 is a partial schematic diagram illustrating a temperature-responsive input circuit according to the present invention;
• FIG. 8 is a graph of V_tempvarofFIG. 7 versus fan voltage showing the desired characteristic;
• FIG. 9 shows partial schematics of a fan connected to an operational amplifier;
• FIG. 10 shows a partial schematic of a fan connected to an open collector operational amplifier and a graph showing the resulting fan voltage curve with temperature changes;
• FIG. 11 shows the partial schematic ofFIG. 10 with the addition of a gain amplifier and a graph showing the resulting fan voltage curve with temperature changes;
• FIG. 12 shows the partial schematic ofFIG. 11 with the addition of circuit to shift the zero point of the fan voltage curve and a graph showing the resulting fan voltage curve with temperature changes;
• FIG. 13 shows the equivalent circuit to the circuit to shift the zero point ofFIG. 12;
• FIG. 14 shows the equivalent circuit to the open collector operational amplifier ofFIG. 12;
• FIG. 15 is a schematic of a first embodiment of the control circuit according to the present invention;
• FIG. 16 is a schematic of a second, alternative, embodiment of the control circuit according to the present invention;
• FIG. 17 illustrates the two output current paths generated by the secondary-output side of transformer T1;
• FIG. 18 is a perspective view of a fully packaged power converter embodying the features described herein;
• FIG. 19 is a cross-section of an illustrative heat sink showing a spring clip to hold a diode in the switch circuit against the heat sink;
• FIG. 20 is an end elevational view of the power converter package ofFIG. 18;
• FIG. 21 is an opposite end elevational view of the power converter package ofFIG. 18;
• FIG. 22 is a top plan view of the switched power converter package ofFIG. 18;
• FIG. 23 is a perspective view of a RV partially broken away to show the switched power converter according to the invention positioned therein;
• FIG. 24 is a perspective view of the heat sink ofFIG. 19 showing a recess or relief in the fan mounting surface.
• FIG. 25 is a photograph of one side of the circuit board used to support the components in the circuit ofFIG. 2 showing heavy wires connected from the center top of the transformer through the circuit board; and
• FIG. 26 is a photograph of the reverse side of the circuit board, with the image reversed to coincide with the orientation of theFIG. 25 photograph, showing the heavy wires from the transformer coming through the circuit board and soldered over the conductive traces leading to the negative output terminal. This photograph also shows additional heavy wires running from the fuses to the positive output terminal and also soldered to and in overlying relation to circuit board traces.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• FIG. 1 is a block diagram of a circuit for a switched power converter embodying the features of the present invention. The block diagram includes an AC-to-DC rectifier circuit10, aswitch circuit12, atransformer circuit14, afeedback circuit16, acontroller18, anover-voltage shutdown circuit20, apermanent over-voltage indicator22, a permanentreverse battery indicator24, athermistor circuit26, avariable speed fan32,fan control circuit30, an,over-temperature shutdown circuit28, a currentsensing feedback circuit34, afoldback circuit42, and an output rectifier andLC filter circuit44 including the inductor L2 referred to hereinafter.
• The AC-to-DC rectifier circuit10 converts a 115v AC line voltage into an unregulated and time-varying dc signal with an average in the 170 volt range. It should be noted that theconverter46 can be plugged into a 170vdc source, if available. In this case therectifier10 performs no rectification functions. The unregulated DC signal then enters the switchingcircuit12 where the on/off states and duty cycle of the switchingcircuit12 is determined by thecontroller18 andfeedback circuits34 and16. The switchingcircuit12 includes two field effect transistors (FET's). The output of the switchingcircuit12 is a regulated waveform containing unidirectional pulses.
• Currentsensing feedback circuit34 is connected to the output of the switchingcircuit12 for the purpose of measuring the output current. The output of thecurrent sensing circuit34 is connected tocontroller18.Controller18 adjusts the duty cycle of the FET's in the switchingcircuit12 according to the current measured by thecurrent sensing circuit34 and the voltage measured bycircuit16. Accordingly, duty cycle is controlled by two factors: voltage feedback viacircuit16 and current feedback viacircuit34.
• Over-voltage shut-downcircuit20 is connected between the output of the AC-to-DC rectifier circuit10 and a shut-down pin of thecontroller18 for the purpose of shutting off the switchingcircuit12 in the event the rectified input voltage at40 exceeds a pre-determined threshold voltage such as 195 vdc. Thepermanent over-voltage indicator22 is connected to the output of the AC-to-DC rectifier circuit10 for the purpose of triggering a permanent indicator in the event the voltage at40 exceeds a second, higher threshold voltage, such as 220 vdc. As noted above, the second threshold voltage will typically be higher than the first, but could be lower or equal to the first threshold voltage. The over-voltage shut-downcircuit20 will protect the costly transistor components of the switchingcircuit12 from being destroyed by the excessive input voltage conditions. Thepermanent over-voltage indicator22 will provide evidence to the manufacturer that an undesirably high AC input voltage had been connected to the converter, e.g., a 220 VAC line voltage. The threshold voltage triggering the over-voltage shut-downcircuit20 is typically lower than the threshold voltage triggering thepermanent over-voltage indicator22, but can be higher or equal to the overvoltage indicator circuit trigger voltage.
• The regulated signal passes from the switchingcircuit12 to thetransformer circuit14. Thetransformer circuit14 steps down the average of the unidirectional pulses to the level necessary for recreational vehicle use; e.g., ultimately to about 13.6 volts. The stepped down waveform is rectified and smoothed bycircuit44 before application to load devices.Feedback circuit16 measures the voltage across the load. The output of thefeedback circuit16 is connected tocontroller18.Controller18 then controls the on/off state and duty cycle of the switchingcircuit12 based in part on the input received from thefeedback circuit16.
• A permanentreverse battery indicator24 is also connected across the DC load for the purpose of providing a physical record that the operator connected a battery in reverse polarity. Such reverse battery connections may cause damage to the switched power converter, and the manufacturer may have an interest in knowing whether the damage was caused by the reverse connection of the RV battery as opposed to a manufacturing defect.
• Thermistor circuit26 senses the temperature of aheat sink52 in thehousing70, and provides a variable resistance based on temperature.Over-temperature shutdown circuit28 receives a signal from thethermistor circuit26 and, if a set-point is exceeded, sends a shutdown signal to thecontroller18.Controller18 then terminates the operation of switchingcircuit12. Theover-temperature shutdown circuit28 will not permit the operation of the switchingcircuit12 until the temperature sensed by the thermistor has fallen below the undesirable temperature limit. Hysteresis in the circuit makes the temperature at which operation is resumed lower than the shutdown temperature.
• Fan control circuit30 receives a signal fromthermistor circuit26. Thefan control circuit30 produces a variable output based on the input from thethermistor26. Avariable speed fan32 is connected to the variable output signal of thefan control circuit30, such that thefan32 will vary in speed based on the input signal. Accordingly, the speed of thefan32 increases in response to increases in sensed temperatures. A low fan speed minimizes the annoying effects of fan noise at low to moderate power levels. The power supply for thefan32 comes from the primary side oftransformer circuit14. This feature eliminates the tendency of the fan supply voltage to droop, with a corresponding fan speed reduction, under heavy load conditions.
• Having briefly described the overall block diagram of the switched power converter circuit, the schematic circuit of an illustrative, mechanical embodiment will be described in detail with reference toFIGS. 2,5 and17. The preferred values of all described electrical components are listed at the end of the detailed description.
• Input Circuit
• Input circuit36 is connected to a conventional AC power supply through a cable having a conventional 3-prong connector. The 3-prong connector includes a ground conductor, a positive conductor, and a neutral conductor. The cable runs into the housing through anaperture100. The AC positive terminal is connected to AC positive input W1. The AC ground terminal is connected to AC ground W2 identified by a “chassis ground” symbol. The AC neutral terminal is connected to AC neutral input W3. AC positive input W1 is connected to thermistor RT2. Thermistor RT2 is used as an inrush current protector for the purpose of protecting fully discharged capacitors from receiving a surge of current. Thermistor RT2 initially (i.e. when cold) provides a high resistance but rapidly changes to a substantially lower resistance as the temperature increases, allowing an unrestricted AC signal to pass into thenoise suppression circuit38. It should be noted that there is a primary ground, secondary ground and a “chassis” ground and that different symbols are used for these inFIG. 2.
• Noise Suppression Circuit
• Thenoise suppression circuit38 includes capacitors C15, C16, C26, C1, C2, C3, C30, C29, and C31, inductor beads L5, L6, L7, and L8, jumpers J6, J7, J8, J9, J10, and J11, and common mode choke (CMC) transformers T3, and T2. These electrical components provide electromagnetic interference noise suppression, and filtering to prevent noise from within the converter from traveling back into the ac supply line. Noise transfer suppression is also provided by capacitors C15, C16, and C26. One plate of C15 is connected to thermistor RT2, and one plate of C16 is connected to AC neutral input line W3. The other plates of capacitor C15, and C16 are connected to chassis ground, i.e., the ground of input W2. Capacitor C26 is connected in parallel to C15 and C16, where one plate of capacitor C26 is connected to thermistor RT2, and the other plate of capacitor C26 is connected to AC neutral input line W3. Both plates of capacitor C26 are connected through CMC transformer T3. Winding2-1 of CMC transformer T3 is connected to thermistor RT2, and winding3-4 of CMC transformer T3 is connected to AC neutral input line W3. The output of winding2-1 is connected to the input side of fuse F1.
• Additional noise suppression is provided by capacitors C1, C2, and C3. One plate of capacitor C1 is connected to the output side of fuse F1, and the remaining plate of capacitor C1 is connected to winding3-4 of CMC transformer T3. Capacitor C1 is also connected to one plate of each of capacitors C2 and C3. The remaining plates of capacitors C2 and C3 are connected to chassis ground. CMC transformer T2 is connected in parallel to capacitors C2 and C3. Winding2-1 of CMC transformer T2 is connected to the ungrounded plate of capacitor C2, and winding3-4 of CMC transformer T2 is connected to the ungrounded plate of capacitor C3. Jumpers J6, J7, J8, are connected in parallel to winding2-1 of CMC transformer T2, and jumpers J9, J10, and J11 are connected in parallel to winding4-3 of CMC transformer T2. All jumpers provide the option of bypassing CMC transformer T2.
• Additional noise suppression is provided by capacitors C30, C29, and C31. The windings of CMC transformer T2 are connected in parallel to capacitor C30. Capacitor C30 is also connected to one plate of each of capacitors C29 and C31. The remaining plates of capacitors C29 and C31 are connected, to chassis ground. High frequency noise suppression is provided by inductor beads L5, L6, L7, and L8. L6 and L8 are fitted onto the bridge connection wires by causing the wires to pass through the center opening of each inductor bead core, wrap around the bead core, and then pass again through the bead core. The wires passing through L6 and L8 are then connected between T2 and a diode bridge DB1 forming the AC-to-DC rectifier10. The inductor beads L5 and L7 are similarly mounted on the wires coming out of the diode bridge DB1 (seeFIG. 2).
• AC-to-DC Rectifier
• The AC-to-DC rectifier10 is composed of a diode bridge DB1, capacitors C4a, C4b,and C4c.The wires passing through L6 and L8 are connected to the input of diode bridge DB1. The wires passing through L5 and L7 are connected to the output of diode bridge DB1. Capacitors C4a,C4b,and C4care connected in parallel between wires passing through inductor beads L5 and L7. The wire passing through L5 is connected to the positive plate of each capacitor C4a,C4b,and C4c,and the wire passing through L7 is connected to the negative plate of each capacitor C4a,C4b,and C4c.The negative plates of capacitors C4a,C4b,and C4care also connected to ground. Under optimal conditions capacitors C4a,C4b,and C4care charged by the output of diode bridge DB1 to a desired voltage of 170 volts. Capacitors C4a,C4b,and C4cprovide an unregulated DC signal tounregulated DC terminal40.
• Permanent Over-Voltage Indicator
• Thepermanent over-voltage indicator22 includes fuse Fx1 and Zener diode D23 connected in series between theoutput40 of rectifier bridge DB1 and ground. Thepermanent over-voltage indicator22 receives the voltage developed across capacitors C4a,C4b,and C4c,and causes the fuse to change state if the voltage across the capacitors reaches an undesirably high level. The cathode of Zener diode D23 is connected to the output of fuse Fx1 and the anode of Zener diode D23 is connected to ground. It will be noted inFIG. 2 there are three different ground symbols. One is chassis ground, connected between C2 and C3 for instance. Another is primary circuit ground, connected to pin12 of U1 for instance. And lastly there is a secondary circuit ground, connected to the output P1 terminal for instance. Each of these three ground symbols refer to separate voltage reference points and are isolated from each other. It will be further noted that the primary ground symbol is subdivided into an S, S2 and P ground. The explanation is:
• S is the signal ground
• S2 is the current sensing circuit ground
• P is the power ground
• In practice, these grounds are separate except at one point in circuit board layout to avoid parasitic noise cross talk. Nevertheless, physically they are the same since they are connected by copper traces and wires. The same is the case for the S and P shown with secondary ground symbol.
• The purpose of thepermanent over-voltage indicator22 is to provide a permanent indication of receiving an undesirably high input voltage greater than that which triggers the over voltage shut downcircuit20. If thepermanent over-voltage indicator22 changes state, it will be because the converter input receives an excessive voltage, caused, for example, by a 220vac supply or runaway generator. If enough voltage is applied to Zener diode D23 it will fail short creating a direct connection between fuse Fx1 and ground. This short failure of D23 causes Fx1 to permanently change state, i.e., blow out to create an open circuit. The preferred voltage limit of thepermanent over-voltage indicator22 is normally 220 volts dc. It will be noted that because theindicator circuit22 is a shunt, failing the diode and blowing the fuse Fx1 does not disable the converter. The term “permanent” is used herein to mean device which does not reset by itself, i.e., it must be replaced to operate a second time. Since tripping the indicator does not shut down the converter, the owner has no reason to replace it and typically will not be aware of its presence. Therefore, it remains in the converter until the converter is returned for service or a warranty claim. For the majority of converters, this never happens. However, for the small percentage of converters returned for a warranty claim, the indicator helps the manufacturer evaluate the likelihood that circuit failures are the result of excessive input voltage other than manufacturing or material defect. If a converter is returned for service and the indicator fuse Fx1 is failed, it will be replaced along with any other failed components and may, for example, signal the need to provide the owner with a cautionary message regarding the quality of the supply voltage source being used.
• Over-Temperature Shut-Down Circuit
• Theover-temperature shutdown circuit28 measures the heat sink temperature in the switched power converter and triggers a shutdown of the switchingcircuit12 upon receiving an undesirably high temperature. Theover-temperature shutdown circuit28 includes Schottky diode D3, resistors R8, RN1B, R7, and RN1A, operational amplifier U3A, and thermistor RT1. Thermistor RT1 changes in resistance based on sensed temperature. Preferably thermistor RT1 is a negative-temperature-coefficient device and is mounted on or in contact with theconverter heat sink52 in the manner shown inFIG. 19; i.e., a spring clip holds the sensor against a surface of the casting which makes up thesink52. Because the FET's in theswitch12 are also mounted in contact with thesink52, heavier load conditions cause the temperature of thesink52 to rise. If turning thefan32 on stabilizes the temperature, no further remedy is needed. It should be noted that the thermistor RT1 does not have to be mounted on the heat sink, but can be mounted to measure, for example, air temperature or the temperature of some component such as thetransformer14 or the output inductor incircuit44. The illustrated arrangement is, however, preferred.
• Operational amplifier U3A is used as a comparator for the purpose of triggering shutdown pin (pin16) ofcontroller18 in the event that the internal temperature of the switched power converter exceeds a set-point temperature. Once shutdown pin (pin16) ofcontroller18 is triggered the operation of switchingcircuit12 is terminated.
• Operational amplifier U3A includes the following connections:pin1 is the output,pin2 is the negative input,pin3 is the positive input,pin4 is connected to a 5 volt reference voltage5REF, andpin11 is connected to ground.Pin2 is connected to a temperature based variable voltage coming from a voltage divider circuit comprised of resistor RN1A and thermistor RT1.Pin3 is connected to a reference voltage through a voltage divider circuit using resistors R8, R7, and RN1B.Pin1 is connected to resistor R8, and Schottky diode D3 leading to shutdown pin (pin16) ofcontroller18.
• The output of operational amplifier U3A will remain at a low (ideally zero) voltage and will not triggershutdown pin16 ofcontroller18 as long aspin3 input does not exceed thepin2 input. When the internal temperature is sufficiently high, the voltage onpin3 will exceed the voltage onpin2 and the output ofpin1 will go high and trigger a shutdown.
• Theover-temperature shutdown circuit28 will operate as follows under a cold temperature condition (i.e. a temperature condition where a thermal shutdown is not required). Resistor RN1A and thermistor RT1 form a voltage divider circuit. Resistor RN1A is connected to a 5 volt reference5REF and thermistor RT1 is connected to ground. Thus,pin2 receives the voltage between resistor RN1A and thermistor RT1. Accordingly, the voltage applied to pin2 will vary depending on the temperature of theheat sink52.
• The value of resistor RN1A is 16.2K ohms, and the value of thermistor RT1 is 100K ohms of 25° C. Thus, when the switched power converter is initially turned on and the temperature is cold the value of thermistor RT1 will be about 100K ohms. At cold startup the voltage applied to thepin2 of operational amplifier is roughly 4.3 volts. Further, at a cold (i.e. non thermal shutdown)temperature pin1 will be near 0 volts because the voltage atpin2 is higher than the voltage atpin3. When the voltage atpin1 is near 0 volts, resistor R8 is parallel with resistor R7.
• In the illustrative embodiment, the values of resistors R8, R7 and RN1B are 499K, 32.4K, and 47.5K ohms respectively. Because resistors R8 and R7 are in parallel, their equivalent resistance at 25° C. is 30.4K ohms. This resistance of 30.4K ohms will be called R_coldtemp. Accordingly, the voltage atpin3 will be the measured voltage between resistor RN1B and R_coldtemp. Using a voltage divider, the voltage applied to pin3 at a cold temperature is 1.925 volts. This voltage will be called V_coldtemp. Accordingly, at a cold temperature the voltage atpin3 will be V_coldtempwhich is 1.925 volts. If the internal temperature significantly increases, the resistance of thermistor RT1 will decrease and the voltage applied to pin2 will fall below the voltage applied to pin3, the output ofpin1 will become positive, and the switched power converter will experience a thermal shutdown.
• Theover-temperature shutdown circuit28 will operate as follows under a thermal shutdown condition (i.e. a temperature condition where an over-temperature shutdown is required). A shut down temperature is never reached if the load on the converter is within normal specifications because thefan32 will provide sufficient cooling. If the load is very heavy and/or the operator has covered theconverter46 with blankets or the like, a shut down temperature may be reached. If this happens, the voltage applied to pin1 will be approximately 5 volts. Whenpin1reaches 5 volts, resistors RN1B and R8 will be in parallel (as opposed to resistor R7 being in parallel with resistor R8 at a cold temperature). The equivalent resistance of resistors RN1B and R8 in parallel is 43.37K ohms. This resistance will be called R_hottemp. Accordingly, the voltage atpin3 will be the measured voltage between resistor R7 and R_hottemp. Using a voltage divider the voltage applied to pin3 at a cold temperature is 2.138 volts. This voltage will be called V_hottemp. Accordingly, in order for the switchingcircuit12 to begin operation the voltage onpin2 must rise above V_hottemp(rather than V_coldtemp). This hysteresis caused by resistor R8 is important so that the switchingcircuit12 will not be enabled until the internal temperature falls significantly below the temperature at which the thermal shutdown was triggered.
• Over-Voltage Shutdown Circuit
• Theover-voltage shutdown circuit20 measures the voltage of capacitors C4a, C4b,and C4c,and will shutdown the switchingcircuit12 in the event of an over-voltage condition atpoint40. Theover-voltage circuit20 includes resistors R38, R39, R40, R7, and RN1B, operational amplifier U3B, and Schottky diode D27. The output of over-voltage shut downcircuit20 is connected toshutdown pin16 ofcontroller18, such that a high signal will terminate the operation ofswitch12. The over-voltage shut-downcircuit20 assures that transistors Q2aand Q2bare not damaged in the event of an undesirably high voltage at the output of the ac-to-dc converter; i.e., atpoint40. As discussed above, there are a number of factors which may cause high voltage conditions to exist. Lightning strikes or transients from other loads on the supply line, unregulated generators, runaway generators and the like may all cause over-voltage conditions.
• Transistors Q2aand Q2bare rated at 500 volts. Because of the properties of transformer T1, transistor elements Q2aand Q2bwill experience a voltage twice that imposed on capacitors C4a,C4b,and C4c.Accordingly, when capacitors C4a,C4b,and C4care at 250 volts, the transistor elements Q2aand Q2bwill experience 500 volts. Accordingly, if the voltage of capacitors C4a,C4b,and C4cexceeds 250 volts transistors Q2aand Q2bmay be damaged.
• Operational amplifier U3B includes the following connections: pin7 is the output,pin6 is the negative input,pin5 is the positive input,pin4 is connected to a 5 volt reference voltage5REF, andpin11 is connected to ground.Pin5 is connected to a voltage divider circuit comprised of resistors R38, R39, and R40. The voltage applied to pin5 will vary depending on the line voltage of capacitors C4a,C4b,and C4c.Pin6 is connected to a reference voltage through a voltage divider circuit comprised of resistors R8, R7 and RN1B. Pin7 is connected to resistor R40, and schottky diode D27 leading toshutdown pin16 ofcontroller18. The output of operational amplifier U3B will remain as a low, ideally zero, voltage and will not trigger shutdown viapin16 ofcontroller18 as long aspin5 input does not exceedpin6 input. When the line voltage of capacitors C4a,C4b,and C4cis sufficiently high, the voltage onpin5 will exceed the voltage onpin6 and the output of pin7 will trigger a shutdown.
• The over-voltage shut-downcircuit20 will operate as follows under a normal voltage condition (i.e. a voltage condition that does not require an over-voltage shutdown). Resistors RN1B and R7 form a voltage divider circuit, where resistor RN1B is connected to a 5 volt reference5REF and resistor R7 is connected to ground. Accordingly,pin6 receives the voltage between resistor RN1B and R7. Remember, that the voltage applied between resistors RN1B and R7 will vary depending upon the operation of the over-temperature circuit28 (i.e. when the temperature is cold resistor R8 is in parallel with resistor R7, and when a thermal shutdown temperature is achieved resistor R8 is in parallel with resistor RB1B). Accordingly, the voltage applied to pin6 will vary depending on whether or not a thermal shutdown temperature is present. However, once a thermal shutdown has been triggered by over-temperature shut-downcircuit28 the operation of theover-voltage circuit20 is irrelevant. Thus, for this explanation it will be assumed that the temperature is below shutdown level and resistor R8 is in parallel with resistor R7.
• In the illustrated embodiment, the values of resistors R8, R7 and RN1B are 499K, 32.4K, and 47.5K ohms respectively. Remembering that at a low temperature resistors R8 and R7 are in parallel, their equivalent resistance is 30.4K ohms. This resistance of 30.4K ohms will be called R_coldtemp. Accordingly, the voltage atpin6 will be the measured voltage between resistor RN1B and R_coldtemp. Using a voltage divider the voltage applied to pin6 at a cold temperature is 1.925 volts. This voltage will be called V_shutdownref.
• In illustrative embodiment, the value of resistors R38, R39, and R40 is 84.5K, 866, and 97.6K ohms, respectively. Prior to an over-voltage shutdown, pin7 will remain at a low, ideally zero, voltage, causing resistor R40 to be in parallel with resistor R39. The equivalent resistance of resistors R39 and R40 in parallel is 858.4 ohms. This resistance of 858.4 ohms will be called R_{normalvoltage}. Pin5 receives the voltage between the voltage divider circuit created by resistors R38 and R_{normalvoltage}. Accordingly, the unregulated DC terminal40 voltage must exceed 195 volts for the voltage atpin5 to exceed V_shutdownref(e.g., if unregulated DC terminal40 carries a voltage of 195 volts,pin5 will be at approximately 1.961 volts which sufficiently exceeds the 1.952 volts applied to pin6). Thus, when theunregulated DC terminal40 reaches a voltage of 195 volts the output, of pin7 will become positive causingcontroller18 to shutdown the switchingcircuit12. Because capacitor voltage is approximately 1.4 times AC line voltage, the illustrative embodiment of theover-voltage shutdown circuit20 will shut down the DC output if the AC input voltage exceeds 140 volts (i.e. the voltage of capacitors C4a, C4b,C4cexceeds 195 volts). Remember that the preferred embodiment of thepermanent over-voltage indicator22 will be triggered at about 220 volts. Accordingly, the output of the switched power converter will be terminated by the over-voltage shut downcircuit20 at a lower over-voltage condition than that which changes the state of the fuse Fx1 in thepermanent over-voltage indicator22.
• Theover-voltage shutdown circuit20 operates as follows under an over-voltage shutdown condition (i.e. the AC input voltage exceeds 140 volts). When a over-voltage shutdown condition is reached, the voltage applied to pin7 is approximately 5 volts. When, pin7reaches 5 volts, resistor R40 is no longer in parallel with resistor R39, but will be used for a hysteresis effect. For example, when pin7 is positive (i.e. over-voltage condition) resistor R40 will provide feedback intopin5, which will in turn increase the voltage atpin5. Accordingly, once operational amplifier U3B triggers a shut down, the voltage atterminal40 must be significantly lower than the 195 volts which triggered the initial shut down because resistor R40 has temporarily increased the voltage measured bypin5. The purpose of the resistor R40 hysteresis is to prevent thecontroller18 from operating the switchingcircuit12 until the voltage atterminal40 has significantly fell below 195 volts.
• Fan control Circuit
• Thefan control circuit30 includes resistors RN1A, R4, RN1C, R2a,R1, and R20, thermistor RT1, operational amplifier U3D, transistor Q1, capacitor C5, and Schottky Diode D1a.FIGS. 2-16 are used to describe the operation of thefan control circuit30 and thefan32. In this embodiment, thefan32 is powered by a dc motor which varies in speed as a function of voltage amplitude; i.e., it is the control circuit which produces the variable speed characteristic. Thefan control circuit30 commands thefan32 to come on at an initial (lowest) temperature. The speed of thefan32 increases with temperature and will maximize at some point prior to the switched power converter being at full load. The fan control circuit is also described in the aforementioned provisional application, attorney docket no. PDY-106-A, the content of which is incorporated herein by reference.
• An operating curve of thefan32 using thefan control circuit30 is shown inFIG. 3. (The slope is not necessarily linear as discussed in more detail herein.) Thefan control circuit30 will cause thefan32 to come on at low speed when temperatures are over the set point by only a small amount.
• The relationship between the voltage applied to the fan and the fan speed is shown inFIG. 4. Due to static friction thefan32 does not start moving until a certain voltage is reached. Specifically, and as illustrated inFIG. 4, the fan blades will not move until the voltage atpoint2 is reached. Compared to the thermal time constants, it more or less instantaneously starts moving, jumping to point3 (initial turn on point). As the voltage increases, it moves to point4, where thefan32 is operating at maximum speed. On the way down, the variable voltage controlledfan32 follows from point4 (maximum operation) to point3 (initial turn on point) to point1 (shut off).
• FIG. 6 illustrates in principle how thefan control circuit30 works. Temperatures T_Hand T_Lare the temperatures at which thefan32 is ideally full on and full off, respectively. More accurately, T_H(line C) is the temperature at which full fan voltage is applied, and T_L(line D) is the temperature at which no voltage is applied to thefan32. Currents belowpoint14 have steady-state operating points on the “fan off” line (line B). currents abovepoint15 have steady-state operating points on the “fan full on” line (line A). Therefore, points14 and15 must be the beginning and end of the line of operating points when operating at currents where the variable voltage controlledfan32 is in an intermediate state between full on and full off. Although a straight line (line E) is shown connecting these two points, the relationship is not necessarily a linear one. It is clearly, however, a strictly increasing (positive slope) function.FIG. 6 illustrates the ideal case.
• Assume the switched power converter starts cold at current operating point I_OP2,point1. The switched power converter will warm up and atpoint2, T_L, thefan32 will start to turn slowly. Theheat sink52 continues to warm up until it reaches its steady-state operating point,point4. Similarly, for current operating point I_OP1, the switched power converter will start atpoint18, thefan32 will come on atpoint6 and settle into a steady speed at point7.
• Turning toFIG. 4, the operating characteristics offan32 are explained. Assume that T_L1corresponds to point1 onFIG. 4 and that T_L2corresponds to point2 onFIG. 4 (same as point3). Thus, returning toFIG. 6, line G describes anactual fan32. Again, this relationship is not necessarily a linear one as shown, but it is a positive slope function. Starting cold with operating current I_OP2, the temperature increases. At point2 (T_L), voltage starts being applied to the variable voltage controlledfan32, but it is not yet moving. At point3 (T_L2) thefan32 begins to rotate. The switched power converter continues to heat up and eventually settles at point5 (along line G). For I_OP1, the switched power converter would start cold atpoint18 and heat up to point6 (T_L). Atpoint6, voltage begins to be applied to thefan32. The switched power converter will continue to heat up until point9 (T_L2), where thefan32 begins moving. Thefan32 will now be moving faster than it needs to, the switched power converter will cool and eventually settle into a steady state speed at point8 (along line G).
• In both cases, thefan32, once started, continues to rotate. There is no discontinuance of operation. Notice further that variable voltage controlledfan32 speeds are slower (and less noisy) for all current levels up to point15 (T_H). Also notice the minimum current to turn thefan32 on corresponds to point17 (T_L2), but if already on, it will stay on to a lower current, corresponding to point16 (T_L1).
• A description of thefan control circuit30 is illustrated inFIGS. 2, and7-16. The preferred embodiment of the fan control circuit includes resistors RN1A, R4, RN1C, R1, and R2a,thermistor RT1, transistor Q1, and operational amplifier U3D. Operational amplifier U3D includes the following connections:pin14 is the output,pin12 is the positive input,pin13 is the negative input,pin11 is connected to ground, andpin4 is connected to a 5 volt reference voltage5REF.
• As illustrated inFIGS. 2, and7, thermistor RT1 is used as a temperature sensor for thefan control circuit30 as well as theover-temperature shutdown circuit28. Thermistor RT1 is connected to ground as well as resistor RN1A which also connected to a 5 volt reference5REF. Thermistor RT1 and resistor RN1A are used to create a voltage divider circuit where V_tempvaris the output of the voltage divider circuit. V_tempvaris connected to pin13 of operational amplifier U3D. Preferably RT1 is a negative-temperature-coefficient thermistor. As the internal temperature increases, V_tempvardecreases. For the remainder of thefan control circuit30, a profile of a desirable fan voltage versus V_tempvaris shown inFIG. 8.
• Because the components used in switched power converter (i.e. operational amplifier U3D) are powered by 5 volts, whereas thefan32 requires a nominal 12 volts, a direct connection of an operational amplifier such as that shown inFIG. 9 will not work. Simply stated an operational amplifier such as operational amplifier U3D cannot supply sufficient current or voltage to thefan32. Neither will transistor emitter follower-type circuits work because of voltage limitations. An open collector operational amplifier would work in a circuit such as that shown inFIG. 10, and a simple gain amplifier would almost provide the desired profile as shown inFIG. 11. Shifting the “zero” point will get the desired profile as shown inFIG. 12. Specifically, a Thevenin resistance and voltage coupled to the negative input of the operational amplifier would shift the zero point of the fan control.
• FIG. 13 illustrates an equivalent of the Thevenin resistance and voltage, and the open collector operational amplifier is shown equivalently inFIG. 14. Using a conventional operational amplifier having an output connected to resistor R1 and transistor Q1 will result in a complete fan control circuit according toFIG. 15. In almost all cases, thefan32 will be quiet, and only under extended high load or high ambient temperature condition will the switched power converter warm up enough to cause thefan32 to be heard.
• Because the circuit inFIG. 15 has a linear range between full on and full off, significant power will be dissipated in transistor Q1 at intermediate fan speeds. An alternative is to modify the linear circuit to act as a duty cycle control circuit as shown inFIG. 16. With duty cycle control, transistor Q1 will be either full on or full off (zero voltage or zero current), but the duty cycle will vary to control the speed of the fan.
• InFIG. 16, resistor R3 adds hysteresis and causes operational amplifier U3D to behave as a comparator. As the switched power converter warms up, transistor Q1 is off until it reaches a “low” temperature. Thefan control circuit30 then breaks into oscillation with low “on” duty cycle on transistor Q1. As the switched power converter continues to warm, the duty cycle gets larger. When an upper temperature is reached, the oscillation stops, and transistor Q1 is always on and stays on as the temperature increases further.
• Thefan control circuit32 as shown inFIG. 2 includes resistors RN1C and R4 acting as a voltage divider circuit connected to pin12 of operational amplifier U3D. Resistor RN1C is connected to 5 volt reference5REF and resistor R4 is connected to ground. The preferred value of resistor RN1C is 9.53K ohms, and the preferred value of resistor R4 is 22.6K ohms. More exactly, the currents flowing through R2awill also contribute to voltage atpin12. Analysis yields
• $\mathrm{VP}1N12=\frac{\frac{+5\mathrm{VREF}}{\mathrm{RNIC}}+\frac{\mathrm{VQ}1C}{R2a}}{\frac{1}{R2a}+\frac{1}{\mathrm{RNIC}}+\frac{1}{{\mathrm{<figure-callout\; label="R"\; filenames="US20080144341A1-20080619-D00004.png"\; state="\{\{state\}\}">R</figure-callout>}}_4}}$
• where R2ahas the preferred value of 453K and VQ1C is the collector voltage of Q1. When Q1 is off and no current flows through the fan, VQ1C can be as high as the voltage in C5, which can vary with line voltage.
• Using a nominal value of 15 volts for the voltage onC5 yields pin12 voltages;
• VPIN12=3.4657 for VQ1c=0 volts
• VPIN12=3.6844 for VQ1c=15 volts
• Thus VPIN12 can more exactly have a range of voltages between 3.4657 and'3.6844 depending on the voltage at the collector of Q1. Atpin13 of operational amplifier U3D, resistor RN2A and thermistor RT1 act as a voltage divider circuit. The preferred value of resistor RN1A is 16.2K ohms, and the preferred value of thermistor RT1 is 100K ohms at a cold start up temperature (25° C.). Accordingly, the initial voltage applied to pin13 at a cold temperature is approximately 4.3 volts, which will be called V_tempvar.
• At the initial startup of the switchedpower converter46, V_tempvaris greater than 3.68v. Thus the output of operational amplifier U3D is near zero causing transistor Q1 to be off and thefan32 is not running. As the temperature increases, the resistance of thermistor RT1 will decrease causing the value of V_tempvarto drop from the initial 4.3 volts. Eventually the temperature will increase such that the value of V_tempvarwill fall slightly below 3.68 volts. When this occurs, the circuit including operational amplifier U3D will enter the linear region. There will be a slight fan voltage but it will probably remain in the stalled condition. If the temperature continues to increase the value of V_tempvarwill fall significantly below 3.68v but above 3.46v and operational amplifier U3D causes the fan to enter the mid speed range. As V_tempvarfalls further, op-amp U3D turns transistor Q1 full on and thefan32 reaches full speed.
• Thefan control circuit30 provides the variable voltage to control the speed of thefan32. Thetransformer circuit14 provides steady power to the power input of thefan32. The power input for thefan32 is connected to pin3 of transformer T1, through Schottky diode D1aand resistor R20. Pin7 of transformer T1 is connected to ground, completing the power input circuit for thefan32. Resistor R20 is used for the purpose of preventing the voltage applied to thefan32 from exceeding specifications. One plate of capacitor C5 is connected to ground and the other plate is connected between resistor R20 and Schottky diode D1afor the purpose of providing a steady voltage to resistor R20. Capacitor C5 is charged by transformer T1 and carries enough voltage to power thefan32. Schottky diode D1aprevents capacitor C5 from discharging intopin3 of transformer T1.
• Because the power input to thefan32 is connected to the primary side of thetransformer circuit14, thefan control circuit30 as well as the variable voltage controlledfan32 will remain operational even when the output is heavily loaded or short circuited. Simply stated, this feature will permit the cooling system of the switched power converter to continue to operate in the event of an over-loaded output. Appropriately, the occurrence of this condition is when the operation of thefan30 is most vital.
Transformer Circuit
• Transformer circuit14 is primarily inclusive of transformer T1.Pin4 of transformer T1 is the positive input fine.Pin4 is connected tounregulated DC terminal40, where the DC line voltage is approximately 170 volts.Pins5 and6 of transformer T1 are connected to the switchingcircuit12. The switchingcircuit12 provides a switching current to the primary-input side of transformer T1. For example, switchingcircuit12, which is controlled bycontroller18, allows current to flow betweenpins4 and5, and betweenpins4 and6. However, the current betweenpins4 and5, and pins4 and6 will never flow simultaneously, but will alternate according tocontroller18. Operation is described below with reference toFIG. 17.
Switching Circuit
• As illustrated byFIGS. 2 and 17, the preferred embodiment of the switchingcircuit12 contains two transistors Q2aand Q2b. When transistor Q2ais turned on current I₁will flow frompin4 of transformer T2 to pin6. Alternatively when transistor Q2bis turned on current I₂will flow frompin4 of transformer T1 to pin5. When transistor Q2ais on transistor Q2bwill be off, and when transistor Q2bis on, Q2awill be turned off. The primary-input side of transformer T1 is utilized in such a fashion so that the transistors within the switchingcircuit12 may operate at up to a maximum 50% duty cycle, meaning that, transistors Q2aand Q2bare never on more than 50% of the time.
• As further illustrated inFIGS. 2 and 17, the secondary-output side of transformer T1 includespins2,8, and1. When current I₂flows betweenpins4 and5 of transformer T1, current I₄will correspondingly flow betweenpins8 and2. Alternatively, when current I₁flows betweenpins4 and6 of the primary-input side of transformer T1, current I₃will correspondingly flow betweenpins8 and1 of the secondary-output side. The switchingcircuit12 further includes R37, R23a, R23band C24 (shown only inFIG. 2).
• Transistors Q2aand Q2bprovide two current loops. Transistor Q2ais connected to pin6 on the primary side of transformer T1, and transistor Q2bis connected to pin5 on the primary side of transformer T1.Controller18 controls the on/off state of transistors Q2aand Q2b. When transistor Q2ais turned on, Q2bis off. Current I₁flows betweenpins4 and6 of transformer T1; alternatively, when transistor Q2bis turned on, Q2ais off and current I₂flows betweenpins4 and5 of transformer T1. The gate of transistor Q2ais connected to resistor R23awhich is connected to AOUT (pin11) oncontroller18. The gate of transistor Q2bis connected to resistor R23bwhich is connected to BOUT (pin14) oncontroller18. Whencontroller18 applies a voltage to the gate of transistor Q2a, transistor Q2aturns on and allow current I₁to flow frompin4 of transformer T1, throughpin6, and then to ground through the drain and source of transistor Q2a. Alternatively, whencontroller18 applies a voltage to the gate of transistor Q2b, transistor Q2bwill turn on and allow current I₂to flow frompin4 of transformer T1, throughpin5 and to ground through the drain and source of transistor Q2b .
• Resistor R37 and capacitor C24 are connected in series between the drain of transistors Q2aand Q2bfor the purpose of snubbing the transient drain voltage when transistors Q2aand Q2bare switching.
Controller
• Controller18 is used for controlling the output of the switching circuit,12 by controlling the duty cycles of switching transistors Q2aand Q2b.Controller18 receives input from thecurrent sensing circuit34, over-voltage shut-downcircuit20, over-temperature shut-downcircuit28,feedback circuit16, andfoldback circuit42.
• As discussed previously, AOUT (pin11) and BOUT (pin14) are connected to transistors Q2aand Q2brespectively for the purpose of controlling the duty cycle and switching current of the switchingcircuit12. SHDN (pin16) is connected to both the output of theover-voltage shutdown circuit20 and theover-temperature shutdown circuit28 for the purpose of terminating the operation of the switchingcircuit12. If SHDN (pin16) receives a sufficient voltage AOUT (pin11) and BOUT (pin14) will turn off transistors Q2aand Q2b, which will terminate the output across the DC load.
• CS+ and CS− are connections to operational amplifier CS, which is internal tocontroller18. The output of operational amplifier CS corresponds to the instantaneous voltage output ofcurrent sensing circuit34. CS+ (pin4) is connected to the output of thecurrent sensing circuit34, which measures the. current through transistors Q2aand Q2b.
• EA+, EA−, and COMP are connections on operational amplifier EA, which is internal tocontroller18. The output of operational amplifier EA is compared to the output of operational amplifier CS. EA+ (pin5), is connected to the output of thefeedback circuit16. EA− (pin6) is connected to COMP (pin7), acting as a voltage follower on operational amplifier EA. Accordingly, the output of operational amplifier EA will be the same as the voltage applied to EA+ (pin5).
• If the instantaneous output of operational amplifier CS exceeds the output of operational amplifier EA AOUT (pin11) and BOUT (pin14) transistors Q2aand Q2bare turned off. If the current generated by transistors Q2aand Q2bexceeds the limit set byfeedback circuit16,controller18 will temporarily terminate the gate drives to Q2 and Q2b. This comparison/control function occurs on a cycle-by-cycle basis.
• CLADJ (pin1) is used to further limit the current output of the switchingcircuit12. The voltage applied to CLADJ (pin1) limits the maximum current output of the switched power converter. As the voltage applied to CLADJ (pin1) decreases so does the maximum current output of the switched power converter. CLADJ (pin1) is connected to the output of thefoldback circuit42, where the foldback circuit will cause the current limit to decrease (i.e. reduce the voltage applied to CLADJ) in a near short circuit situation. CLADJ (pin1) is also connected between resistors R14 and R15 which act as a voltage divider circuit. Resistor R14 is connected to 5 volt reference5REF and is in series with resistor R15. Resistor R15 is also connected to ground.
• VREF (pin2) provides a 5.1 volt reference voltage which supplies power to various electrical components within the switched power converter. The output of VREF is identified as 5 volt reference5REF. VIN (pin15) is connected to a power supply for the purpose of providing power tocontroller18. VIN (pin15) is connected to Zener diode D9 and capacitor C10 which provide approximately 15 volts tocontroller18. Zener diode D9 and capacitor C10 receive voltage from unregulated DC terminal40 through resistors R24aand R24b.
• VC (pin13) is the power supply for the sales of transistors Q2aand Q2bthrough AOUT (pin11) and BOUT (pin14), respectively. VC (pin13) is connected to VIN (pin15) through resistor R16. Resistor R16 is used to limit the current entering VC (pin13). Schottky diodes D16a, D15a,D15band D16bare used to prevent the voltage on AOUT (pin11) and BOUT (pin14) from exceeding VIN or from dropping below GND.
• GND (pin12) is connected to ground. Capacitor C25 is connected to CT (pin8) and resistor R13 is connected to RT (pin9) for setting the frequency and maximum duty cycle ofcontroller18. Capacitor C25 and resistor R13 are also connected to ground. SYNC (pin10) is not utilized.
Foldback Circuit
• As briefly mentioned,foldback circuit42 provides feedback tocontroller18 for the purpose of reducing the duty cycle of transistors Q2aand Q2bunder near short circuit conditions rather than allowing the output current across the DC toad to increase out of control.Foldback circuit42 includes, diode D4, resistors R19a, R19b, R17, and R18, capacitor C8, and operational amplifier U3C. Operational amplifier U3C has the following connections:pin8 is the output,pin9 is the negative input,pin10 is the positive input,pin4 is connected to 5 volt reference5REF, andpin11 is connected to ground.
• Thefoldback circuit42 measures the duty cycle of transistors Q2aand Q2b.Pin10 is connected to AOUT (pin11) and BOUT (pin14) oncontroller18 through resistors R19aand R19b.
• Capacitor C8, which is connected betweenpin10 and ground, as well as in series with resistors R19aand R19bis used for the purpose of averaging the duty cycle controlled gate voltages of transistors Q2aand Q2b. Resistor R17 is connected between 5 volt reference5REF andpin10, and resistor R18 is connected betweenpin10 and ground for the purpose of creating a voltage divider circuit to reduce the voltage applied to pin10.Pin9 is connected to pin8 for the purpose of creating a voltage follower, such that the voltage atpin8 will always equal the voltage applied to pin10.Pin8 is also connected to the cathode of diode D4, and the anode of diode D4 is connected to CLADJ (pin1) ofcontroller18.
• As the duty cycle of AOUT (pin11) and BOUT (pin14) increases, the voltage of capacitor C8 increases as well as the voltage onpin10. Accordingly, the voltage onpin8 will be higher than the voltage between resistors R15 and R14. When this occurs, diode D4 will be reverse biased and the voltage at CLADJ (pin1) ofcontroller18 will not be affected. In this situation the current limit of CLADJ will neither decrease nor increase becausefoldback circuit42 is not pulling current from CLADJ (pin1).
• As the duty cycle of AOUT (pin11) and BOUT (pin14) decreases, the voltage of capacitor C8 decreases as well as the voltage onpin10. Accordingly, the voltage onpin8 will be lower than the voltage between resistors R15 and R14. When this occurs, diode D4 will be forward biased and the voltage at CLADJ (pin1) ofcontroller18 will be pulled down. As the voltage applied to CLADJ (pin1) decreases, the maximum current output ofcontroller18 will also decrease. Accordingly, in the event of a near short circuit at the DC load, the reduced current limitation of CLADJ will prohibit the current output from going unreasonably high and reduce the output current to less than its previous maximum rating.
Voltage Feedback Circuit
• Thefeedback circuit16 measures the voltage across the DC load and outputs a reference voltage tocontroller18.Controller18 contains an internal voltage controller, for the purpose of providing a voltage controlled current source.Controller18 will control the switching of transistors Q2aand Q2baccordingly.Feedback circuit16 includes resistors R28, R34, R32, R26, R25, R33 and R30, capacitors C27, C22, C20, and C28, and optical coupler U2 which includes a LED, a photo-sensor and a 2.5 volt reference.
• When the DC load is increased, there is an immediate drop in voltage across the DC output terminals of the power converter. This drop in voltage requires an increase of output current in theoutput circuit44 in order to meet the new load demands. Alternatively, when the DC load is decreased, there is an immediate increase in voltage. This increase in voltage requires a decrease in the output current of theoutput circuit44 in order to compensate for the load reduction.
• For example, when the operator of the switched power converter brings an additional load on-line, thefeedback circuit16 first measures the voltage across the load and then scales the voltage down to a 2.5 volt range. Because a new load has been added the measured voltage will be below the 2.5 voltage range. Optical coupler U2 will compare the measured voltage (scaled down) against a 2.5 volt reference. Because the measured voltage across the load will be below the 2.5 reference voltage, optical coupler U2 will cause the LED to produce less light. When the LED produces less light the photo-sensor will cause the output of the feedback circuit to increase in voltage. The output of the photo-sensor is connected to EA+ (pin5) oncontroller18. When the voltage input of EA+ (pin5) increases, the voltage controller withincontroller18 will temporarily increase the duty cycle of the switchingcircuit12. This in turn increases the load current to meet the new load demand (i.e. get the voltage across the DC load back up to 13.6 volts).
• Alternatively, when the operator of the switched power converter removes a load, thefeedback circuit16 measures the voltage across the load and then scales the voltage down to a 2.5 volt range. Because a load has been removed the measured voltage will be above the 2.5 voltage range. Opto-coupler U2 will compare the measured voltage (scaled down) against a 2.5 volt reference. Now, because the measured voltage across the load will be above the 2.5 reference voltage, opto-coupler U2 will cause the LED to produce additional light. When the LED produces additional light the output of the feedback circuit will decrease in voltage. The output of the photo-sensor is connected to EA+ (pin5) oncontroller18. When the voltage input of EA+ (pin5) decreases, the voltage controller withincontroller18 will temporarily decrease the duty cycle of the switchingcircuit12. This in turn, decreases the load current to meet the reduced load demand (i.e. get the voltage across, the DC load back down to 13.6 volts).
• Resistor R25 limits current to opto-coupler U2. Resistor R26 and R28 are arranged as a voltage divider to provide a scaled output voltage in the vicinity of 2.5 volts. Capacitors C20, C22, C27, C28, R34, R32 and R33 are used for stability, do not affect the DC levels whatsoever as they carry no DC current. Resistor R30 is used for providing an input voltage to EA+ (pin5) ofcontroller18 based on the current output of opto-coupler U2.
Current Sensing Circuit
• Current sensing circuit34 is used to measure the current being drawn by transistors Q2aand Q2band to send the measured current to CS+ (pin4) ofcontroller18.Controller18 then compares this measured current to a reference level. The reference level is the output offeedback circuit16, which is connected to EA+ (pin5) oncontroller18. Depending upon the measured current and the reference level,controller18 will control the on/doff state of transistors Q2aand Q2b.
• Current sensing circuit34 includes transformer T4, diodes D24a, D24b, D24c, and D24d, resistors R21, R21a, R21b, R21c, R21d, and R21e, and capacitor C9. The drain of transistor Q2bis connected to pin4 of transformer T4, and the drain of transistor Q2ais connectedpin6 of transformer T4. The output side of transformer T4 (pins1 and2) is connected to a series of diodes and resistors and then to CS+ (pin4) ofcontroller18.
• Diodes D24a, D24b, D24c, and D24dmake up a full wave rectifier bridge. Diodes D24cand D24bare connected in parallel to the output side of transformer T4, where the cathode of diode D24cis connected to pin1 of transformer T4 and the cathode of diode D24bis connected to pin2 of transformer T4. The anodes of diodes D24band D24care both connected to ground. Diodes D24dand D24aare also connected in parallel to the output side of transformer T4, where the anode of diode D24dis connected to pin1 of transformer T4 and the anode of diode D24ais connected to pin2 of transformer T4. The cathodes of diodes D24aand D24dare connected to CS+ (pin4) ofcontroller18 as well as a series of resistors and a capacitor.
• For example, when transistor Q2ais turned on, the current from transformer T4 will flow frompin1 of the transformer, through diode D24dand through resistors R21, returning through D24bto pin2. A voltage representing the flow of this current trough R21 is connected to pin4 of CS+ incontroller18. When transistor Q2bis turned on, the current from transformer T4 will flow frompin2 of the transformer through D24aand through R21 (to ground) and then returning through R24cto ground topin1 of T4. Again, the voltage on R21 resistors is fed to CS+, the op-amp incontroller18.
• Resistors R21, R21a, R21b, R21c, R21d, and R21e, and capacitor C9 are all connected in parallel. The current output of diodes D24dand D24aare connected to the high side of resistors R21, R21a, R21b, R21c, R21d, and R21e, and capacitor C9. The low side of resistors R21, R21a, R21b, R21c, R21d, and R21e, and capacitor C9 are connected to ground. This parallel resistor-capacitor circuit is used for the purpose of ensuring the voltage applied to CS+ (pin4) ofcontroller18 is in the 1 volt range.
Output Circuit
• The secondary-output side of transformer T1 is connected to the DC load through a series of circuit elements making up the output rectifier andLC filter circuit44. Theoutput circuit44 includes capacitors C19, C11, C13A, C12, C14A, C17, and C18, schottky diodes D11aand D11b,diode D12, resistor R29, inductor L2, fuses F2, F3, and F4, inductor beads L3, L4, L10, and L11, andheavy gauge wires105,106, and107. The DC load is connected in parallel with capacitors C11, C13A, C12, C14A, C17, and C18 (DC load capacitors), which are in series with inductor L2. Theoutput circuit44 is integral with the transformer secondary and includes two current loops with the current going in the same direction through inductor L2, the DC load capacitors, and the DC load (FIG. 17).
• As further illustrated byFIG. 17 when transistor Q2ais turned on (Q2bis off) current I₁will flow betweenpin4 and pin6 (primary-input side of transformer T1) in a counter-clockwise direction. Current I₁will cause current I₃to flow betweenpin8 and pin1 (secondary side of transformer T1) in a clockwise direction. Alternatively, when transistor Q2bis turned on (Q2ais off) current I₂will flow betweenpin4 and pin5 (primary-input side of transformer T1) in a clockwise direction. Current I₂will cause current I₄to flow betweenpin8 and pin2 (secondary side of transformer T1) in a counter-clockwise direction. As illustrated the current (I₄and I₃) applied to inductor L2 is always going in the same direction.
• Further explained, when transistor Q2ais turned on, current flows in the secondary-output side of transformer T1 frompin1 through schottky diode D11a,through inductor L2. The DC load capacitors will be charged and current will be delivered to the DC load and back throughpin8 of the transformer. When transistor Q2bis turned on, current flows in the secondary side of transformer T1 frompin2 through schottky diode D11b,through inductor L2, the DC load capacitors will be charged and current will be delivered to the DC load and then back throughpin8 of the transformer.
• Resistor29 and capacitor C19 are connected in series between secondary-output pins2 and1 of transformer T1 for the purpose of eliminating transient voltages. Inductor beads L3, L4, L10, L11, are connected between the secondary-output side of transformer T1 and schottky diodes D11aand D11b.Inductor beads L3, L4, L10 and L11 are placed on the leads of D11A and D11B, for the purpose of reducing transient noise. The DC load capacitors which are connected in parallel with the DC load are arranged as follows. Capacitor C11 is the main output capacitor. The positive plate of capacitor C11 is connected to the positive terminal of the DC load P4 and the negative plate is connected to the negative terminal of the DC load P1.
• The remaining capacitors are used for the purpose of reducing noise. Capacitor C12 is connected in parallel with the DC load, where one plate of capacitor C12 is connected to the positive terminal of the. DC load P4, and the other plate of capacitor C12 is connected to the negative terminal of the DC load P1. Capacitors C13A and C14A are connected in series, where one plate of capacitor C13A is connected to the positive terminal of the DC load P4, and one plate of capacitor C14A is connected to the negative terminal of the DC load P1. The remaining plates of capacitors C13A and C14A are connected to chassis ground. Capacitors C17 and C18 are also connected in series, where one plate of capacitor C17 is connected to the positive terminal of the DC load P4, and one plate of capacitor C18 is connected to the negative terminal of the DC load P1. The remaining plates of capacitors C17 and C18 are connected to chassis ground. Fuses F2, F3, and F4 are connected in series with inductor L2 and work in conjunction with diodes D11aand D11bto provide reverse battery protection.
• The illustrated embodiment of this invention also includes the use of heavy gauge wires which supplement the copper laminations on the circuit board. Heavy gauge wires105 are connected directly between the negative output (terminal8) of transformer T1 and the negative terminal of DC load P1 (i.e. DC negative output88)Heavy gauge wires106 are connected directly between schottky diodes D11A and the input of inductor L2.Heavy gauge wires106 are also connected directly between schottky diodes D11B and the input of inductor L2. Heavy gauge wires107 are connected directly between the output of inductor L2 and fuses F2, F3, and F4. The output of fuses F2, F3, and F4 are connected to the positive terminal of DC load P4 (i.e. DC positive output90).
Waveforms
• FIG. 5 illustrates waveforms found at various points in the circuit ofFIG. 17 under normal operating conditions.FIG. 5A shows the voltages across the two power transistors Q2aand Q2bduring a complete cycle of operation. One voltage is the complement of the other.FIG. 5B shows the voltages across the primary windings of transformer T1 during one complete cycle of switch operation.FIG. 5C illustrates the current waveforms I₁and I₂through the primary loops ofFIG. 17.
• FIG. 5D shows the current through inductor L2.
• FIG. 5E shows the secondary current through diode D11a.
• FIG. 5F shows the secondary current14 through diode D11b.
• FIG. 5G shows the current through C11.
• FIG. 5H shows the voltage at the top of the circuit ofFIG. 17; i.e., the top of L2.
• Permanent Reverse Battery Indicator
• The permanent reversebattery connection indicator24 is diode D12. Diode D12 and capacitor C11 are connected in parallel. The cathode of diode D12 is connected to the positive plate of capacitor C11 which is connected to the positive terminal of the DC load P4. The anode of diode D12 is connected to the negative plate of capacitor C11 which is connected in to the negative terminal of the DC load P1. If a reverse battery connection is applied to the DC load output of the power converter, diode D12 will blow before fuses F2-F4 open circuit, permanently indicating that a reverse battery connection has occurred. If F2-F4 blow, they may be replaced or reset and theconverter46 will be fully operational even if D12 is not replaced.
Packaging a Commercial Device
• Having described the preferred power conversion circuit, the packaging of a commercial embodiment will be described in detail with reference toFIGS. 18-26.
• The commercial embodiment ofconverter46 comprises a rectangularsheet metal housing70 attached by screws to afinned aluminum extrusion52 which forms the aforementioned heat sink for the FET's Q2aand Q2b,diode D11aand D11b,and the thermistor RT1. These components are held against a largeflat surface53 ofheat sink52 byspring clips55 which are screwed into the heat sink extrusion in the manner shown inFIG. 19. Thefan32 is mounted by screws57 onto an end of theheat sink extrusion52 in which arelief59 of circular design has been machined. The surfaces of therelief59 lie below the end surfaces61 of thefins65 and thescrew base63 on which thefan32 is mounted. This relief creates an air gap between the fan motor50 and the heat sink which prevents heat from the sink reaching the fan motor.Numerous vents58 are formed in the top and back plates of thehousing70.
• Flanges84 are provided on both ends ofhousing70 for mounting purposes. Fuses F2-F4 are mounted outside thehousing70 for ease of replacement. Fuse Fx1, however, is inside the housing for reasons described above. Thepositive output terminals90 and thenegative output terminals88 are mounted on the left side ofhousing70 as shown inFIG. 22. Apower cord98 extends fromhousing70 throughaperture100.
• The components in the circuit ofFIG. 2 are mounted on aconventional circuit board102 which is secured by fasteners withinhousing70. Theboard102 has conductive traces on both sides as shown inFIGS. 25 and 26. The inductor L2 is mounted onboard102 as shown inFIG. 25 along with the transformer T1.(central inFIG. 25). Two No. 12gauge wires104 run from the center tap of T1 to apoint106 where they pass through a hole inboard102 and emerge on the other side as shown inFIG. 26. From there to thenegative output terminal88 the wires overlie a copper trace and are soldered to the trace to lower the resistance of this high current path and increase the robustness of it as well. The leads108 from L2 to the fuses F2-F4 and thepositive outputs90 are similarly constructed.
• FIG. 23 shows theconverter46 mounted within an RV109 having astorage battery114. Apower cord112 brings 115 vac to the converter from a pedestal111 of the type found in RV parks. Theconverter46 is connected into the electrical system of the RV in a known manner.
• Referring again toFIG. 2 the circuit for theconverter46 is here equipped with a 4-wire terminal H2 of whichpin4 is connected to the converter output fuses. F2-F4 via a 100 Ohm resistor R57. The terminal H2 allows the converter to be connected to an external “management” system of the type described in U.S. Pat. No. 5,982,643 issued Nov. 9, 1999 to Thomas H. Phlipot and assigned to Progressive Dynamics, Inc. As is more completely described in the '643 patent, the management system includes a microcontroller which gives the owner the option of various operating modes and various converter output voltages; e.g., 13.6 v for normal operation, 13.2 v for storage, and 14.4 v for boost.
Miscellaneous—Options
• FIG. 2 also illustrates a terminal H4 connected to ground via R51, R31 and C21. Terminal H4 is a two-contact terminal which is shorted out with a small bridge wire if a gel cell is used in place of the normal lead-acidliquid storage battery114 in the RV. This lowers the operating voltages of theconverter46 by 0.4 v and is a convenient option for owners who wish to use gel cell storage batteries
• While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law. It is also to be understood that it is the inventor's intent to claim all novel subject matter contained within this disclosure.

• VALUES OF LISTED COMPONENTS

  C1	Capacitor	0.47	uF
  C10	Capacitor	220	uF
  C11	Capacitor	16	V
  C12	Capacitor	0.01	uF
  C13A	Capacitor	0.01	uF
  C14A	Capacitor	0.01	uF
  C15	Capacitor	2.2	nF
  C16	Capacitor	2.2	nF
  C17	capacitor	0.047	uF
  C18	capacitor	0.047	uF
  C19	capacitor	0.001	uF
  C2	capacitor	2.2	nF
  C20	capacitor	0.015	uF
  C22	capacitor	0.47	uF
  C24	capacitor	270	pF

  C25

  capacitor

  0.12 uF, 2%

  C26	capacitor	0.47	uF
  C27	capacitor	1000	pF
  C28	capacitor	0.1	uF
  C29	capacitor	2.2	nF
  C3	capacitor	2.2	nF
  C30	capacitor	0.47	uF
  C31	capacitor	2.2	nF

  C4a	capacitor	820 uF, 250 V
  C4b	capacitor	820 uF, 250 V
  C4c	capacitor	820 uF, 250 V
  C5	capacitor	100 uF, 35 V

  C7	capacitor	0.1	uF
  C8	capacitor	0.1	uF
  C9	capacitor	0.01	uF
  D10	zener diode	13	V

  D11a	schottky diode	40 A, 100 V
  D11b	schottky diode	40 A, 100 V

  D12

  diode

  D15a	schottky diode	1 A, 20 V
  D15b	schottky diode	1 A, 20 V
  D16a	schottky diode	1 A, 20 V
  D16b	schottky diode	1 A, 20 V
  D1a	schottky diode	1 A, 100 V
  D23	zener diode	220 V, 5 W, 5%
  D24a	diode	75 V, 150 mA
  D24b	diode	75 V, 150 mA
  D24c	diode	75 V, 150 mA
  D24d	diode	75 V, 150 mA
  D27	schottky diode	1 A, 20 V
  D3	schottky diode	1 A, 20 V
  D4	diode	75 V, 150 mA
  D9	zener diode	15 V, 2 W
  DB1	diode bridge	20 A, 400 V Bridge

  F1	fuse	15	A
  F2	fuse	30	A
  F3	fuse	30	A
  F4	fuse	30	A
  Fx1	fuse	0.5	A
  L2	inductor	20	uH

  Q1	transistor	5 A, 40 V
  Q2a	transistor	24 A, 500 V, .20 on resistance
  Q2b	transistor	24 A, 500 V, .20 on resistance
  R1	resistor	390 Ohm, 5%

  R13	resistor	1.82	K
  R14	resistor	16.2	K
  R15	resistor	35.7	K

  R16

  resistor

  1.8 K, 5%

  R17	resistor	5.49	K
  R18	resistor	15.4	K
  R19a	resistor	12.1	K
  R19b	resistor	12.1	K

  R20

  resistor

  50 Ohm, 5%, 3 W

  R21	resistor	18.7	Ohm
  R21A	resistor	422	Ohm
  R21B	resistor	422	Ohm
  R21C	resistor	845	Ohm
  R21D	resistor	845	Ohm
  R21E	resistor	1690	Ohm

  R23a	resistor	15 Ohm, 5%
  R23b	resistor	15 Ohm, 5%
  R24a	resistor	1.5 K, 5%, 10 W
  R24b	resistor	1.5 K, 5%, 10 W
  R25	resistor	1 K, 5%, ½ W
  R26	resistor	31.2 K or 30.1 K
  R28	resistor	6.98 K, ¼%
  R29	resistor	10 Ohm, 5%

  R2a	resistor	453	K
  R30	resistor	4.7	K
  R33	resistor	3.24	K
  R34	resistor	3.24	K

  R37	resistor	100 Ohm, 5%, 10 W
  R38	resistor	84.5 K, 0.5 W

  R39	resistor	866	Ohm
  R4	resistor	22.6	K
  R40	resistor	97.6	K
  R7	resistor	32.4	K
  R8	resistor	499	K
  RN1A	resistor	16.2	K
  RN1B	resistor	47.5	K
  RN1C	resistor	9.53	K
  RT1	thermistor	100	K
  RT2	thermistor	1	Ohm

  T1	transformer	2:13:13:2:2
  T2	CMC transformer	custom
  T3	CMC transformer	custom

  T4

  transformer

  80

  MH

  U2	optically isolated amplifier	FOD2741
  USA	operational amplifier	LM2902
  U3B	operational amplifier	LM2902
  U3C	operational amplifier	LM2902
  U3D	operational amplifier	LM2902

Claims (17)

1. A power converter having an input for receiving a supply voltage, a switch, and a duty cycle controller connected to control the switch to regulate an output voltage produced by the converter wherein the improvement comprises:

a first circuit connected to said input and responsive to a first level over-voltage condition at said input for altering operation of duty cycle controller; and

a second circuit connected to said input and responsive to a second level over-voltage condition at said input to irreversibly change state without altering operation of the duty cycle controller.

2. A converter as described inclaim 1 wherein the second level is higher than the first level.

3. A power converter as described inclaim 1 wherein the first circuit comprises an amplifier, circuit connected to said input and to a reference voltage, said amplifier circuit having an output connected to said controller to shut, said controller down in response to the first level over-voltage condition.

4. A power converter as described inclaim 1 wherein the second circuit comprises the series combination of a non-resettable fuse and a Zener diode connected between said input and ground.

5. A power converter having an input connectible to an AC line voltage source, a rectifier for converting an AC line voltage to DC, a switching circuit comprising at least one power transistor, a transformer having a primary side connected to said rectifier and to said switch circuit and a secondary side connected to a converter output, a controller circuit for operating said switch circuit in a variable duty cycle mode wherein the improvement comprises:

a permanent over-voltage indicator circuit connected between said rectifier and ground and including the series combination of a voltage responsive semi-conductor device and an element which irreversibly changes state in response to the presence of an over-voltage condition at said rectifier output.

6. The power converter described inclaim 5 wherein said element is a fuse.

7. The power converter described inclaim 5 wherein said semi-conductor device is a Zener diode.

8. The power converter ofclaim 5 further comprising an over-voltage shut-down circuit connected between said rectifier output and said controller for shutting the controller down under over-voltage conditions.

9. The power converter ofclaim 8 wherein said over-voltage shut-down circuit further includes an operational amplifier.

10. A power converter comprising an input for receiving a supply voltage, a switch including at least one power transistor, and a duty cycle controller connected to cycle the switch on and off; an over-voltage shut-down circuit connected between said input and said controller and comprising an operational amplifier; said operational amplifier having an output, connected to a shut down pin of said controller to terminate cycling of the switch.

11. A power converter for charging a battery and having a switch, a duty cycle controller connected to the switch, a transformer having a primary side and a secondary side, an output inductor, the primary side being connected to the switch and the secondary side being connected to the output inductor, a circuit for indicating a reverse battery connection and comprising a device connected between the output inductor and ground and effective to irreversibly change state when a reverse battery connection is made.

12. A power converter as defined inclaim 11 further including a capacitor connected in parallel with said device.

13. A power converter as defined inclaim 12 wherein the device is a Schottky diode.

14. A power converter comprising a switch, a controller for controlling the duty cycle of the switch, a transformer, an output inductor and a converter output terminal;

a circuit board having conductive traces formed thereon, the inductor being mounted on the current board such that at least one conductive trace runs from the inductor to the output terminal; and

a heavy gauge wire conductively bonded to and along said one conductive trace.

15. A power converter comprising a switch, a controller for controlling the duty cycle of the switch, a transformer, an output inductor and a converter output terminal;

a circuit board having conductive traces formed thereon, at least one trace running from the transformer to the output terminal; and

a heavy gauge wire conductively bonded to and along said one conductive trace.

16. A power converter including a switch, a controller for varying the duty cycle of the switch, a heat sink for the switch, a fan for causing the fan to cause air to flow over the heat sink;

a heat sensor; and

a fan control circuit, the fan control circuit being operative to control the supply voltage source to vary the speed of the fan in response to increasing temperature of said sensor.

17. The power converter defined inclaim 16 wherein the fan comprises a motor mounted proximate the heat sink, the heat sink comprises a metal extrusion having a recess machined into an end thereof to provide an air gap between the heat sink and the fan motor.

Images