US20130141012A1 - LED-Based Lighting Power Supplies With Power Factor Correction And Dimming Control - Google Patents

Abstract

A power supply for powering one or more loads includes a boost circuit with power factor correction (PFC) that provides an operating voltage from an electrical power source, and a dimmer detection circuit that determines a dimming level applied to the electrical power source, and generates a pulse width modulated (PWM) signal based upon the dimming level. The power supply also includes one or more current control circuits, each current control circuit being associated with each of the one or more loads, and coupled in series with the operating voltage, its associated load, and a ground of the power supply, so as to control a current through its associated load in response to the PWM signal.

Description

RELATED APPLICATIONS
• This application is a divisional application of U.S. patent application Ser. No. 12/859,717, filed Aug. 19, 2010, which claims priority to U.S. Provisional Patent Application Ser. No. 61/235,101, filed Aug. 19, 2009. Both of the above-identified patent applications are incorporated herein by reference.
BACKGROUND
• The power factor of an AC electric power system is defined as the ratio of the real power (voltage and current in phase) flowing to a load, to apparent power (voltage and current out of phase), and is a number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 power factor=50% power factor). Real power is the capacity of a circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Energy stored in the load and returned to the source, or non-linearities in the load that distort the wave shape of the current drawn from the source, often cause the apparent power to be greater than the real power. A load with low power factor draws more current than a load with a high power factor for the same amount of useful power transferred, and thereby causes higher resistive losses in wiring. It is therefore desirable to correct power factor for many types of load.
• Non-linear loads, such as rectifiers, distort the current drawn from the system into a non-sinusoidal waveform. Non-linear loads require active power factor correction to counteract the distortion and raise the power factor. Power factor correction may occur within equipment at a central substation, within equipment throughout a distribution system, or may be performed within power-consuming equipment.
• A typical switched-mode power supply, as found in many consumer products, first powers a DC bus, using a bridge rectifier or similar circuit. The output voltage is then derived from this DC bus. Since rectifiers are non-linear devices, the input current is highly non-linear and has a low power factor resulting from energy at harmonics of the frequency of the voltage. Regulatory agencies such as the EU have set harmonic limits as a method of improving power factor. Declining component cost has hastened implementation of power factor correction. To comply with current EU standard EN61000-3-2, all switched-mode power supplies with output power more than 75 W must include power factor correction (PFC). 80 PLUS power supply certification requires power factor to be corrected to 0.9 or greater.
• To achieve a higher power factor, Active Power Factor Correction (active PFC) is used to control the amount of power drawn by a load, in order to obtain a power factor as close as possible to unity. In most applications, the active PFC controls the input current of the load so that the current waveform is proportional to the mains voltage waveform (a sine wave).
• Some types of active PFC are: Boost circuits, Buck circuits, and Buck-boost circuits, and may be implemented as single-stage or multi-stage. In the case of a switched-mode power supply, an active PFC circuit may use a boost converter inserted between the bridge rectifier and the main input capacitors. The boost converter attempts to maintain a constant DC bus voltage on its output while drawing a current that is always in phase with and at the same frequency as the line voltage. Typically, a second switched-mode converter inside the power supply produces the desired output voltage from the DC bus voltage. This approach requires additional semiconductor switches and control electronics, but permits using cheaper and smaller passive components than passive PFC. Switched-mode power supplies with passive PFC can achieve power factor of about 0.7-0.75, whereas switched-mode power supplies with active PFC, may achieve a power factor up to 0.99. Without PFC, switched mode power supplies typically have a power factor of about 0.55-0.65.
• FIG. 1 shows one exemplary priorart power device100 with controlled output power and power factor correction (PFC).Power device100 is shown driving aload114. Afirst section102 ofdevice100 implements PFC and asecond section104 provides anisolated output voltage108 through atransformer106. In this example, an integrated circuit NCP1603 facilitates PFC withinfirst section102 and includes a pulse width modulation (PWM) circuit to implement the secondary switched-mode power conversion, withinsecond section104, as commonly used in power supply devices.
• In this example,load114 operates at avoltage112 that is provided by avoltage regulator110 which uses anoutput voltage108 ofsecond section104.Second section104 operates in a switched-mode to generatevoltage108 fromtransformer106.Second section104 includes optical feedback to the integrated circuit which operates to maintainvoltage108 irrespective of current drawn byload114 and voltage supplied byfirst section102. At startup ofdevice100,first section102 operates to produce anoperating voltage105 to supplysecond section104. To avoid startup problems wheresecond section104 overloadsfirst section102 when attempting to providevoltage108, and hence voltage113 to load114, the integrated circuit typically delays the start ofsecond section104, for between 0.5 and 3 seconds, to allowfirst section102 to attainoperating voltage105. Whereload114 represents a lighting application, such startup delay is undesirable.
• Further, in this example,output voltage108 ofdevice100 may contain ripple fromsecond section104, sincesecond section104 operates by generating an alternating current throughtransformer106.
• As shown,device100 includesvoltage regulator110 to reducevoltage108 tovoltage112 as required byload114. Wherevoltage112 is varied to control operation of load114 (i.e.,voltage regulator110 operates to vary voltage112), power loss in the form of dissipated heat fromvoltage regulator110 may be undesirable. For example, using the simple equation of “watts=amps*volts”, wherevoltage108 is 20V and current drawn byload114 is 1 A at 10V, power dissipation byvoltage regulator110 is 10 W, which result in an efficiency of only 50% (since power used byload114 is 10 W) or less fordevice100.
• In particular, wherevoltage112 supplied to load114, and hence current throughload114, varies, efficiency ofdevice100 is dependent on the voltage drop across, and current through,voltage regulator110. The greater the voltage drop across the regulator, the greater the power loss and the lower the efficiency.
• An issue currently confronting LED manufacturers and the LED lighting industry is the sensitivity of human perception to the properties of LED light, and the difficulty of precise process control in LED manufacturing such that spectral differences among LEDs are not objectionable in lighting products. At the present time, LED manufacturers and the LED lighting industry are working together to identify and segregate LEDs with specific spectral properties such that end users can select appropriately “warm” or “cool” LED lighting, and so that mixtures of LEDs with differing spectral properties do not present a nuisance or distraction within a fixture or across fixtures in an installation. It is typical for LED lighting manufacturers to carefully order LEDs from single LED manufacturer batches and to track them for use in particular light fixture orders. The present necessity to do so can have negative implications for inventory management and production scheduling—that is, it is expensive and/or risky to build “to stock” because product can become useless if the product built does not include a specific batch of LEDs needed for a future order.
SUMMARY
• In an embodiment, a power supply for powering a load includes a boost circuit with power factor correction (PFC) that derives an operating voltage from an electrical power source, a current control circuit that controls a current through the load, and a voltage control circuit that generates a feedback voltage to the boost circuit to control the operating voltage. The feedback voltage is controlled to be substantially equal to the sum of (a) a voltage required across the load to drive the current through the load, (b) half of a maximum peak-to-peak voltage of a ripple on the operating voltage, and (c) a minimum voltage drop across the current control circuit. The current control circuit operates to control the current through the load with minimal heat loss from the current control circuit and without ripple on the current.
• In another embodiment, a method drives a load using a boost circuit with power factor correction (PFC), a current control circuit, and a voltage feedback circuit. Electrical power is received at the boost circuit and an operating voltage is generated, based upon a voltage feedback signal, within the boost circuit. The current through the load is controlled using a current sink of the current control circuit that is connected in series with the load. The current sink is controlled based upon a difference between a first voltage across a sense resistor of the current control circuit connected in series with the load, and a reference voltage representative of a desired current through the load. The voltage feedback signal is generated based upon a second voltage sensed at the current sink such that the operating voltage produced by the boost circuit is substantially equal to the sum of (a) a voltage drop produced across the load by the current through the load, (b) half of a maximum peak-to-peak voltage of a ripple on the operating voltage, and (c) a minimum voltage drop across the current control circuit. Current through the load is substantially continuous.
• In another embodiment, a power supply for powering one or more loads includes a boost circuit with power factor correction (PFC) that provides an operating voltage from an electrical power source, and a dimmer detection circuit that (a) determines a dimming level applied to the electrical power source, and (b) generates a pulse width modulated (PWM) signal based upon the dimming level. The power supply also includes one or more current control circuits, each current control circuit being (c) associated with each of the one or more loads, and (d) coupled in series with the operating voltage, its associated load, and a ground of the power supply, so as to control a current through its associated load in response to the PWM signal.
• In another embodiment, a method for driving at least one load using a boost circuit with power factor correction (PFC), a dimmer detection circuit, and a current control circuit includes receiving electrical power at the boost circuit and generating an operating voltage within the boost circuit from the electrical power. The method also includes generating, within the dimmer detection circuit, a pulse width modulated (PWM) signal indicative of the dimming level, and controlling the current through the load using a switch of the current control circuit that is connected in series with the load, the switch being controlled based upon the PWM signal.
• In another embodiment, a method for manufacturing LED-based lighting products includes manufacturing power supply subsystems for the lighting products, receiving a customer order, including an LED specification, for the lighting products, stocking LEDs to match the LED specification, manufacturing LED-based lighting fixtures that utilize the LEDs, and integrating the power supply subsystems with the LED-based lighting fixtures to form the lighting products.
• In another embodiment, a method for manufacturing LED-based lighting products includes manufacturing power supply subsystems for the lighting products and manufacturing cabling operable to connect the power supply subsystems with LED-based lighting fixtures. The method also includes receiving a customer order, including an LED specification, for the lighting products, stocking LEDs to match the LED specification, manufacturing LED-based lighting fixtures that utilize the LEDs, and shipping sets of the power supply subsystems, the cabling and the LED-based lighting fixtures to fill the customer order.
BRIEF DESCRIPTION OF THE FIGURES
• FIG. 1 shows one prior art power converter with power factor correction.
• FIG. 2 is a block diagram illustrating one exemplary linear driver with power factor correction, in an embodiment.
• FIG. 3 shows exemplary components and connectivity of the boost converter circuit ofFIG. 2, in an embodiment.
• FIG. 4 shows exemplary components of the voltage feedback circuit ofFIG. 2, in an embodiment.
• FIG. 5 shows exemplary components of the current control circuit ofFIG. 2, in an embodiment.
• FIG. 6 shows exemplary components of the current control interface ofFIG. 2, in an embodiment.
• FIG. 7 shows one exemplary load formed as a lighting unit with fifteen light emitting diodes (LEDs).
• FIG. 8 shows one exemplary method for driving a load using a boost circuit with power factor correction (PFC), a current control circuit, and a voltage feedback circuit.
• FIG. 9 shows one exemplary lighting system formed as a power supply that provides power to, and AC dimming control of, one or more lighting fixtures, in an embodiment.
• FIG. 10 is a block diagram showing exemplary functionality of the power supply ofFIG. 9.
• FIG. 11 shows exemplary waveforms of AC power and associated waveforms generated by the AC dimming sense filter ofFIG. 10.
• FIG. 12 shows the boost converter ofFIG. 9 in exemplary detail.
• FIG. 13 is a schematic showing exemplary detail of the lighting fixture ofFIG. 9.
• FIG. 14 shows the AC dimming sense filter ifFIG. 10 in exemplary detail.
• FIG. 15 shows exemplary connectivity of the microcontroller and circuits ofFIG. 10.
• FIG. 16 is a flowchart illustrating one exemplary method, implemented within the microcontroller ofFIG. 10, for controlling the PWM dimming signal, in an embodiment.
• FIG. 17 is a flowchart illustrating one exemplary method of manufacturing LED-based lighting products, in an embodiment.
DETAILED DESCRIPTION
• FIG. 2 is a block diagram illustrating oneexemplary power supply200, having a linear driver and power factor correction, driving aload208.Load208 is shown in dashed outline as it is not considered part ofpower supply200, which can power many different types of load.Power supply200 includes a boost converter circuit (with power factor correction)202, avoltage feedback circuit204 and acurrent control circuit206.Boost converter circuit202,voltage feedback circuit204 andcurrent control circuit206 cooperate to control current throughload208. In particular,voltage feedback circuit204 andcurrent control circuit206 form alinear regulator circuit207 that controls current throughload208 and minimizes power loss by regulating output voltage ofboost converter circuit202.
• Boost converter circuit202 receives alternating current (AC) power viaAC input210 and generates a positive direct current (DC)output214 with reference to anegative DC output212.Boost converter circuit202 also generates a secondpositive DC output216, with reference tonegative DC output212, that provides power for operating internal components ofcircuits202,204 and206.
• Boost converter circuit202 providespositive DC output214 at a voltage based upon a voltage feedback signal222 fromvoltage feedback circuit204.Voltage feedback circuit204 generatesvoltage feedback signal222 based upon a sensed voltage of current through acurrent path218, which is provided bycurrent control circuit206 to return current fromload208 throughnegative DC output212.
• Optionally,power supply200 may include acurrent control interface230 to control current throughcurrent path218 viacurrent control circuit206. In particular,current control circuit206 controls current throughcurrent path218 based upon a pulse width modulated (PWM)control signal234. One exemplarycurrent control interface230 may be found in US Patent Application Publication No. 2010/0079262 A1 of U.S. patent application Ser. No. 12,238,705, filed Sep. 26, 2008, titled “Systems and Methods for Conveying Information Using a Control Signal Referenced to Alternating Current (AC) Power”, incorporated herein by reference.
• FIG. 3 shows exemplary components and connectivity ofboost converter circuit202 ofFIG. 2.Circuit202 includes anintegrated circuit controller330, a bridge rectifier formed of fourdiodes302,304,306 and308, a filter circuit formed of twocapacitors310,312, aresistor314 and aninductor316, as shown. Adiode318, aresistor320,decoupling capacitors322,350 and aregulator324 provide regulated power for second DC output216 (also seeFIG. 2) and forintegrated circuit controller330. One example ofintegrated circuit controller330 is NCP1601, available from ON Semiconductor®.
• Integratedcircuit controller330,resistors332,334,336,348,capacitors338,340,342,344,bulk capacitors356,358,360,362,364, adiode354, field-effect transistor (FET)346, and aninductor352 operate as a boost circuit to generatepositive DC output214 and negative DC output212 (also seeFIG. 2) based uponvoltage feedback signal222.Bulk capacitors356,358,360,362, and364 are charged viadiode354, to maintain a desired voltage forpositive DC output214.
• In one embodiment, exemplary values of components withincircuit202 are:diodes302,304,306,308 and354 each may be SS24-D from ON Semiconductor;capacitors310 and312 each may have a value of 0.1 μF, 100V;decoupling capacitor322 may have a value of 47 μF, 50V;capacitor338 may have a value of 1000 μF;capacitor340 may have a value of 0.1 μF;capacitor342 may have a value of 330 μF;capacitor344 may have a value of 100 μF;decoupling capacitor350 may have a value of 0.1 μF;capacitor356 may have a value of 0.1 μF, 100V electrolytic;capacitors358,360,362, and364 each may have a value of 100 μF, 100V electrolytic;diode318 may be a BAL99LT1;inductors 316 and 352 may have values 150 μF and 33 μF, respectively;resistors320,332,334,336,348 may have values 0.2 ohms, 33 ohms, 1K ohms, 0.067 ohms, and 10 ohms, respectively;regulator324 may be a78L15 15V regulator; integratedcircuit controller330 may be a NCP1601, available from ON Semiconductor; andtransistor346 may be a ZXMN10A25G.
• FIG. 4 shows exemplary components and connectivity ofvoltage feedback circuit204. Anamplifier402 is configured withcapacitor412 andresistors410 and404 to integrate a sensed voltage of current path218 (also seeFIG. 2) and to drive a base oftransistor414. An emitter and collector oftransistor414 serially connect within a chain ofresistors420,418 and416 betweenpositive DC output214 andnegative DC output212 such that a voltage ofvoltage feedback signal222, betweenresistors418 and420, is controlled based upon a voltage ofcurrent path218 with reference topositive DC output214. A pair ofresistors422 and424 form a voltage divider betweensecond DC output216 andnegative DC output212 to generate areference voltage426 that is input toamplifier402 via aresistor428.
• In one embodiment, exemplary component values are:amplifier402 may be a LM358D;transistor414 may be a BC846B;resistors404,410,416,418,420,422,424 and428 may have values 100K ohms, 1K ohms, 1K ohms, 20K ohms, 10K ohms, 10K ohms, 2K ohms and 100K ohms, respectively; andcapacitor412 may have a value of 1 μF.
• FIG. 5 shows exemplary components and connectivity ofcurrent control circuit206 ofFIG. 2.Current control circuit206 includesresistors518,520, and522 that are serially connected betweensecond DC output216 and negative DC output212 (also seeFIG. 2) and generate a reference voltage at apoint525.Current control circuit206 also includes anamplifier502,resistors506,524 and acapacitor504 that are configured to integrate the reference voltage atpoint525 and to drive a base of acurrent sink transistor514 via aresistor516. The reference voltage atpoint525 also connects to a first lead of acapacitor526, and a second lead ofcapacitor526 connects tonegative DC output212, such thatcapacitor526 prevents rapid change in the reference voltage. A collector ofcurrent sink transistor514 providescurrent path218, and an emitter oftransistor514 connects to acurrent sense resistor512, which in turn connects tonegative DC output212 to provide a return path forcurrent path218. Sensedcurrent signal508, at the emitter oftransistor514, is fed back toamplifier502 via aresistor510.Amplifier502 operates to control current through sense resistor512 (and hence current path218) usingtransistor514 to maintain a voltage of sensedcurrent signal508 substantially equal to the reference voltage atpoint525.
• Whenpower supply200 includes current control interface230 (seeFIG. 2),current control circuit206 includes acurrent control input529. A collector of an optional transistor530 connects to a common junction ofresistors518 and520, an emitter of transistor530 connects tonegative DC output212 and a base of transistor530 connects tocurrent control input529 to receivePWM control signal234.PWM control signal234 drives the base of transistor530 to vary the voltage reference atpoint525 which in turn causesamplifier502 to control current throughcurrent sink transistor514, thereby controlling a current through load208 (FIG. 2).
• Referring again toFIG. 2, sincevoltage feedback signal222 is used withinboost converter circuit202 to controlpositive DC output214,voltage feedback circuit204 provides direct feedback based upon sensed current throughload208. Voltage ofpositive DC output214 is controlled byvoltage feedback circuit204 such that any ripple in the voltage ofpositive DC output214 has no effect on current through transistor514 (FIG. 5), and such that excessive power is not dissipated bytransistor514.Transistor514 operates close to saturation to minimize voltage drop acrosstransistor514. Thus,voltage feedback circuit204 andcurrent control circuit206 operate differently from conventional linear regulation wherein excess voltage is typically dropped across the linear regulator, and thus power dissipates as heat.
• In one embodiment, exemplary component values are:amplifier502 may be a LM358D;transistor514 may be a BC846B;resistors506,510,512,516,518,520,522, and524 may have values 4.99K ohms, 4.99K ohms, 2.495 ohms, 1K ohms, 4.99K ohms, 150K ohms, 4.99K ohms, and 4.99K ohms, respectively;capacitors504,526 and528 may have values 1000 μF, 0.1 μF, and 0.1 μF, respectively; and transistor530, if included, may be of type BC846A.
• FIG. 6 shows exemplary components and connectivity of optionalcurrent control interface230. As noted above, further information on use of an exemplary control signal referenced to an AC supply may be found in US Patent Application Publication No. 2010/0079262 A1.Current control interface230 has tworesistors602,604, connected between lines ofAC input210 to form areference voltage603 that is substantially at a midpoint (in terms of voltage) between voltages of lines ofAC input210. The emitter of aPNP transistor606 connects to referencevoltage603, and a base oftransistor606 connects tocurrent control signal232 via aresistor608 and toreference voltage603 via aresistor610. Adiode612 connects between the base oftransistor606 andreference voltage603 to prevent excessive reverse bias oftransistor606 fromcurrent control signal232. A collector oftransistor606 connects to a first end of aresistor616; the other end ofresistor616 providesPWM control signal234. Aresistor618 connects betweennegative DC output212 andPWM control signal234 such thatPWM control signal234 is pulled ‘low’ whentransistor606 turns off. Acapacitor614 decouplesreference voltage603 with respect tonegative DC output212. In operation, ascurrent control signal232 toggles, substantially between voltages of lines ofAC input210,PWM control signal234 toggles substantially between voltages ofnegative DC power212 andreference voltage603.
• In one embodiment, exemplary component values are:transistor606 may be a BC856A;diode612 may be a BAL99LT1;capacitor614 may have a value of 1 μF; andresistors602,604,608,610,616 and618 may have values 10K ohms, 10K ohms, 470K ohms, 470K ohms, 100K ohms, and 33K ohms, respectively.
• FIG. 7 shows one exemplary load formed as a lighting unit with fifteen LEDs702(1)-(15) connected in series betweenpositive DC output214 andcurrent path218. Light emitted byLEDs702 is based upon current flowing through the LEDs, and thus is controlled bycurrent control circuit206 andvoltage feedback circuit204. Althoughload208 is shown with fifteenLEDs702,load208 may consist of any number of LEDs and/or other components. That is,power supply200 may provide power to any type of DC load. In the embodiment ofFIG. 7,current control signal232 may represent a dimming signal for controlling brightness of light output byLEDs702.LEDs702 may each be NS6L083BT-H1_S811 from Nichia.
• In one example of operation,voltage feedback circuit204 controls boostconverter circuit202 to outputpositive DC output214 with a voltage substantially 2.5 volts higher than a voltage dropped acrossload208 for a desired current throughload208. This 2.5 volts represents a minimum voltage drop across thecurrent control circuit206, plus half of a maximum peak-to-peak ripple voltage onpositive DC output214. By controlling the voltage ofpositive DC output214, power loss (through heat dissipation) is minimized withincurrent control circuit206 sincetransistor514 operates close to saturation (minimum resistance), but with sufficient variance to eliminate voltage ripple withinpositive DC output214. For example, an operating voltage provided bypositive DC output214 is controlled to be substantially equal to a minimum voltage drop acrossload208 for a desired current throughload208, plus half of an estimated maximum peak-to-peak ripple voltage, plus a minimum voltage drop across current control circuit206 (e.g., a minimum voltage drop acrosstransistor514 and resistor512).Current control circuit206 thus removes any ripple voltage by controlling current throughload208. Thus, one advantage ofpower supply200 is thatload208 is powered with direct current with substantially no ripple, while power loss bypower supply200 is minimized through use ofvoltage feedback signal222 to control the voltage ofpositive DC output214 fromboost converter circuit202.
• A further advantage ofpower supply200 is thatlinear regulator circuit207 does not preventboost converter circuit202 from reaching operation voltage (as with prior art circuits that use boost conversion type circuits) and thereby reduces circuit complexity and timing. In particular, the use of a constant current load limits the current drawn fromboost converter circuit202 upon startup, whereas a constant power circuit, as typically used in the prior art, draws higher current when operating voltage is lower, and thereby overloads its boost conversion stage. For example,power supply200 has less than the typical 0.5-3 second delay that is imposed by prior art circuits to enable their boost conversion stage to reach an operational voltage prior to activation of the constant power circuit.Power supply200 minimizes such turn-on delays and avoids unstable operating conditions. In one example of operation,power supply200 achieves a full operational current throughload208 within 100 mS from application of electrical power toAC input210. In particular,power supply200 incurs a delay caused by the initial charging ofbulk capacitors356,358,360,362, and364, which are nominally charged within a few (e.g., between two and four) cycles of power input toAC input210.
• In one embodiment,circuit202 incorporates active power factor correction using an ON Semiconductor NCP1601 integrated circuit (seeintegrated circuit controller330,FIG. 3). This provides a DC voltage higher than the peak of the AC input that is then used by an LED driver stage. The problem with the LED driver being a standard high efficiency LED driver is that the PFC stage needs to be up to operating voltage before the LED driver is turned on. If this is not done, the LED driver loads the PFC stage and it never gets up to voltage. If a conventional linear regulator is used in stead of a high efficiency switcher, the overall efficiency is low and the additional thermal load would challenge fixture designs. If the LEDs were powered directly off the PFC output, the LED current would not be continuous, as there is several volts of ripple in the PFC output, even with large electrolytic filter capacitors.
• The present design uses a linear regulation design in a second regulation stage to provide a constant current through connected LEDs (the load) and to remove ripple from the PFC output. However, unlike conventional circuits where voltage input to a linear regulator is constant, the voltage supplied to the linear regulator ofcircuit202 is controlled to be about 2.5 volts higher than a desired voltage across the load, thus the linear regulator removes any ripple in the supplied voltage without dissipating excessive heat through voltage drop across the regulator. That is, output of a PFC stage is controlled to provide a voltage across the load and regulator that does not require excessive voltage to be dropped by the regulator to provide the desired current through the load. This leads to high efficiency, since the voltage dropped across the linear regulator is never greater than a minimum voltage drop needed to substantially remove ripple in voltage from the PFC stage. Further, since the current through the load is controlled linearly, when current through the load is reduced (e.g., through operation of optional transistor530 and within current control circuit206) it is still continuous and not modulated (e.g., through pulse width modulation) as in conventional lighting control. Thus, there is no “strobe effect” with lighting controlled by this circuit.
• FIG. 8 shows oneexemplary method800 for driving a load using a boost circuit with power factor correction (PFC), a current control circuit, and a voltage feedback circuit.Method800 may represent operation ofpower supply200,FIG. 2.
• Instep802,method800 receives electrical power at the boost circuit and generates an operating voltage, based upon a voltage feedback signal, within the boost circuit from the electrical power. In one example ofstep802,boost converter circuit202 receives electrical power fromAC input210 and generates positive direct current (DC)output214 with reference tonegative DC output212.
• Instep804,method800 controls the current through the load using a current sink of the current control circuit coupled in series with the load, the current sink being controlled based upon a difference between a first voltage sensed by a sense resistance of the current control circuit connected in series with the load and a reference voltage representative of a desired current through the load. In one example ofstep804,current control circuit206 usescurrent sink514 to control current throughload208 based upon a difference between a voltage sensed acrosssense resistor512 and a reference voltage atpoint525.
• Instep806,method800 generates the voltage feedback signal, used instep802, based upon a second voltage sensed at the current sink such that the operating voltage produced by the boost circuit is substantially equal to the sum of (a) a voltage drop across the load for the current through the load, (b) half of a maximum peak-to-peak voltage of ripple on the operating voltage, and (c) a minimum voltage drop across the current control circuit. In one example ofstep806,voltage feedback circuit204 generatesvoltage feedback signal222 based upon a sensed voltage ofcurrent path218 such thatpositive DC output214 has a voltage substantially equal to the sum of the voltage drop acrossload208, half of the maximum peak-to-peak ripple onpositive DC output214, and a minimum voltage drop acrosscurrent control circuit206. Power loss, dissipated as heat bycurrent control circuit206, is minimized while ripple is substantially removed frompositive DC output214 and current throughload208 is substantially continuous.
• Lighting System with AC Dimming Control
• FIG. 9 shows oneexemplary lighting system900 formed as apower supply902 that provides power to, and AC dimming control of, one ormore lighting fixtures904.Power supply902 receives AC power910 (e.g., 24V AC) from atransformer924 connected to AC power920 (e.g., 110V AC) via anAC dimmer922.AC dimmer922 represents a conventional dimming device that connects to mains AC power (e.g., AC power920) for controlling brightness (e.g., by dimming) AC powered lighting for example.Power supply902 convertsAC power910 into DC power (e.g., 48V DC) and provides a PWMdimming control signal918. The DC power andPWM dimming signal918 are output in combination on a threerail bus911.Bus911 has a positive rail912 (e.g., 48V), a ground rail914 (e.g., 0V), and PWMdimming control signal918.
• Power supply902 includes aboost converter906 with power factor correction (PFC) that generates DC power onpositive rail912 with respect toground rail914, and a PWMdimming signal generator908 that generates PWMdimming control signal918 based upon detected AC dimming (e.g., as provided by AC dimmer922) ofAC power910.Bus911 connectspower supply902 to eachlighting fixture904. As shown inFIG. 9,bus911 may pass through eachlighting fixture904 such thatlighting fixtures904 may be connected using a ‘daisy chain’ technique.
• FIG. 10 is a block diagram showing exemplary functionality ofpower supply902 ofFIG. 9. WithinFIG. 10, not all power (e.g.,operational power932 and second operational power934) and ground (e.g., ground914) connectivity is shown for clarity of illustration.AC power910 is rectified infull wave rectifier1002 and output as rectifiedpower938 to boostcircuit1004, which generates DC power for output ontopositive rail912 with respect toground rail914 ofbus911. Operation ofboost circuit1004 is based upon operational power932 (e.g., 15V DC) received from a high-voltage input range, low drop-out,regulator1006 that is powered from boost circuit1004 (e.g., positive rail912). Startup ofboost circuit1004 andregulator1006 results from application ofAC power910 topower supply902, whereinpositive rail912 quickly reaches the voltage of rectified power938 (e.g., 24V DC).Regulator1006 utilizes this power to generateoperational power932 that starts operation ofboost circuit1004, which raises the voltage ofpositive rail912 to its desired voltage (e.g., 48V).Regulator1006 is designed to operate over a large input voltage range (e.g., between a voltage just above its designed output voltage of 15V to the 48V output of boost circuit1004) to maintain operation ofboost circuit1004.
• Operational power932 fromregulator1006 also provides power to alow voltage regulator1008 that in turn provides a second operational power934 (e.g., 3V or 5V DC) to a microcontroller1010 (and components ofpower supply902 that operate from the lower voltage).Microcontroller1010 receives adimming indication signal1013 that is indicative of AC-dimming ofAC power910 from an AC-dimmingsense filter1012. AC dimmer922 (seeFIG. 9) represents a typical AC dimmer (e.g., using triacs or thyristors) for controlling dimming of lighting.
• FIG. 11 shows exemplary waveforms ofAC power910 and associated waveforms generated by AC dimmingsense filter1012. A typical non-dimmedAC voltage waveform1102 has a substantially sinusoidal shape that crosses a zero voltage line at zero-crossing points1106 and1108. In the following example, leading edge waveform modification is illustrated. However, AC dimming based upon trailing edge waveform modification is also detected by AC-dimmingsense filter1012. That is, AC-dimmingsense filter1012 functions with most standard AC dimmers currently on the market to generate dimmingindication signal1013.
• AC voltage waveform1102 ofFIG. 11 may representAC voltage920 ofFIG. 9. As shown onwaveform1110, whereAC dimmer922 is set to “dim” lighting, turn on of each AC power cycle is delayed from zerocrossing points1106 and1108 to turn onpoints1116 and1118, respectively. The greater the ‘dimming’ level applied byAC dimmer922, the greater the delay is between zero-crossing points1106 and1108 to turn onpoints1116 and1118, respectively. In one example of operation, AC-dimmingsense filter1012first rectifies waveform1110 to formwaveform1120, which is then passed through a filter circuit (e.g., a low frequency low-pass filter) that generates dimmingindication signal1013, a DC level of which is indicative of the AC dimming level ofAC voltage910 imparted byAC dimmer922. In one example of operation, as the AC dimming level imparted ontoAC power910 by AC dimmer922 increases, the DC level ofdimming indication signal1013 decreases.
• Referring back toFIG. 10,microcontroller1010 periodically samples and converts (e.g., using an internal analog-to-digital converter) dimmingindication signal1013 into a digital value indicative of the AC dimming level imparted byAC dimmer922.Microcontroller1010 may utilize algorithms, such as filtering and averaging, for further processing of these digital values to determine the AC dimming level imparted byAC dimmer922, and then generate a PWMdimming control signal1011 that has a pulse width based upon the AC dimming level determined from dimmingindication signal1013. PWM dimming control signal is converted intoPWM dimming signal918 by aPWM signal driver1014.
• As is typical of triac based dimmers,AC dimmer922 may function erratically when insufficient current is drawn at high dimming levels (e.g., 90% or greater), which often results in unwanted flickering of conventional lighting controlled by the AC dimmer. Sincelighting fixtures904 utilize LED based lighting, loading ofAC power910 is significantly lower in comparison to where conventional incandescent illumination is utilized, which could exacerbate the erratic behavior of AC dimmer922 at high AC dimming levels. Therefore,power supply902 may include anAC load1016 under control ofmicrocontroller1010.Microcontroller1010 controlsAC load1016 to draw additional current directly from rectifiedpower938 when the determined AC dimming level is high (e.g., greater than 90%), thereby reducing erratic function ofAC dimmer922.
• Power supply902 may also include a boostperformance sense circuit1018 that receives anintegrator signal936 ofboost circuit1004 and provides aboost performance signal1019 indicative of operation ofboost circuit1004 tomicrocontroller1010.Microcontroller1010 may periodically sample and convert (e.g., using an internal analog-to-digital converter)boost performance signal1019 into a digital value that is indicative of performance ofboost circuit1004. For example, performance ofboost circuit1004 may vary during a startup period ofpower supply902 and also when loading ofpositive rail912 changes as a result of changes in AC dimming level that changes power drawn frompositive rail912 by eachconnected lighting fixture904. One or more algorithms withinmicrocontroller1010 may utilize the determined performance ofboost circuit1004 when determining PWMdimming control signal1011, for example to prevent too rapid a dimming change withinlighting fixtures904.
• Optionally,power supply902 may include atemperature sensor1020 that provides atemperature signal1021 indicative of temperature ofpower supply902 tomicrocontroller1010.Microcontroller1010 may periodically sample and convert (e.g., using an internal analog-to-digital converter)temperature signal1021 into a digital value indicative of temperature ofpower supply902.Microcontroller1010 may include algorithms and rules that modifyPWM dimming signal918 based upon determined temperature ofpower supply902. For example, microcontroller may increase the dimming level of PWMdimming control signal1011 to reduce loading ofpower supply902 bylighting fixtures904 if temperature ofpower supply902 exceeds a defined maximum temperature threshold.
• Optionally,power supply902 may include one ormore input circuits1022 for receiving information via aninput signal1032 from external circuitry.Input circuit1022 may generate aninput signal1023 that conveys information frominput signal1032 to microcontroller1010 (e.g., converting a signal range ofinput signal1032 into a range suitable formicrocontroller1010.Microcontroller1010 may periodically sample and convert (e.g., using an internal analog-to-digital converter) eachinput signal1023 into one or more digital values for evaluation. In one example,input circuit1022 receivesinput signal1032 from a motion detector (not shown) that provides information of detected movement within an area monitored by the motion detector.Microcontroller1010, upon evaluatinginput signal1023, may (a) increase dimming level ofPWM dimming signal918 when no movement is indicated for a defined period to reduce illumination provided by lighting fixtures904 (e.g., to save power), and/or may (b) reduce the dimming level ofPWM dimming signal918 when movement is indicated, to provide additional illumination from lighting fixtures904 (e.g., to illuminate the area). In another example,input circuit1022 receives information from a CO₂sensor (or a smoke detector), whereuponmicrocontroller1010 controls PWM dimmingsignal918 to flash illumination fromlighting fixtures904 as a warning if the information indicates danger.
• FIG. 12 shows boostconverter906 ofFIG. 9 in exemplary detail.FIG. 12 is best viewed withFIGS. 9 and 10 and the following description. Fourdiodes1204 are configured as a full-wave bridge rectifier1002 to provide rectifiedpower1205 that is positive with respect toground rail914.Regulator1006 is formed withresistors1206,1208,1214,1218,1220,1222, and1228, acapacitor1226,NPN transistors1216 and1224, and aPNP transistor1210, and outputsoperational power932, as shown. Boost circuit1004 (seeFIG. 10) is formed with anintegrated circuit controller1234,resistors1232,1238,1246, and1254,capacitors1230,1236,1248,1250,1252,1256,1258,1260, and1262, aninductor1240, adiode1242, andFET1244.Boost circuit1004 receives power from rectifiedpower1205 and operates to boost the rectified power voltage to providepositive rail912.
• Aregulator1270 anddecoupling capacitors1272 and1274 are connected to formlow voltage regulator1008 that provides secondoperational power924 fromoperational power932.
• Upon startup ofcircuit906,capacitor1248 is initially charged from rectifiedpower1205 viainductor1240 anddiode1242 to a voltage that allowsregulator1006 to produceoperational voltage932. Onceoperational voltage932 is present, integratedcircuit controller1234 commences operation to boostpositive rail912 to a designed operational voltage (e.g., 48V).Integrator signal936 is derived from the connection betweencapacitor1258 andresistor1254 that connect in series to form an integrator input tointegrated circuit controller1234.
• In one embodiment,diodes1204 may be dual power Schottky diodes. Resistors1206,1208,1214,1218,1220,1222, and1228 may have values of 1K ohms, 20 ohms, 4.99K ohms, 2K ohms, 82.5K ohms, 2K ohms, and 82.5K ohms, respectively.Capacitor1226 may have a value of 0.1 μF at 100V.NPN transistors1216 and1224 are each a BC849, andPNP transistor1210 is a power transistor. Integratedcircuit controller1234 is for example an NCP1601, available from ON Semiconductor. Resistors1232,1238,1246, and1254 may have values of 1K ohms, 220K ohms, 10 ohms, and 10K ohms, respectively.Capacitors1230,1236,1248,1250,1252,1256,1258,1260, and1262 may have values of 3.3 μF 50V, 1000 μF, 4700 μF 63V, 1.0 μF 100V, 0.1 μF 100V, 0.01 μF, 0.1 μF, 470 μF, and 150 μF, respectively.Inductor1240 may have a value of 10.0 μB,diode1242 may be a V10P10 277A, andFET1244 may be of type FQPF70N10.Regulator1270 is for example a 78LSOT89R, anddecoupling capacitors1272 and1274 may each have a value of 0.1 μF.
• FIG. 13 is a schematic diagram showing exemplary detail oflighting fixture904 ofFIG. 9. A control input of anintegrated circuit controller1302 receives PWMdimming control signal918 via a conditioning circuit formed ofresistors1304 and1306 andNPN transistor1308.Controller1302, in cooperation with aresistor1318,capacitors1314,1316,inductor1322 anddiode1312, controls current through a load formed ofLEDs1324 connected in series. A maximum output current ofcontroller1302 is set by resistor1318 (connected between the VIN and SET input pins of controller1302). For example, ifresistor1318 has a resistance of 0.23 ohms, the maximum current throughLEDs1324 is 865 mA. In another example, ifresistor1318 has a resistance of 0.5 ohms, maximum current throughLEDs1324 is 400 mA.Resistor1318, as shown inFIG. 13, may represent more than one resistor connected in parallel. The twelveLEDs1324 shown inFIG. 13 are exemplary, and more or fewer LEDs may be used withinlighting fixture904 without departing from the scope hereof.
• Dimming is achieved by applying PWMdimming control signal918 at the CTRL input pin ofcontroller1302. An input voltage of 0.2V or lower at CTRL input of controller1302 (e.g., whenPWM dimming signal918 is held in a high state) switches off the output and putscontroller1302 into a low-current standby state. Anoptional diode1320 betweenpositive rail912 andground rail914 prevent reverse voltage being applied tolighting fixture904.Lighting fixture904 may also include afuse1310 for additional overload protection.
• In one embodiment,controller1302 is for example an AP8802 step-down DC/DC converter from Diodes Incorporated. Resistors1304 and1306 may each have a value of 10.0K. NPN transistor1308 may be a BC849.Resistor1318 is selected to define a maximum current throughdiodes1324 oflighting fixture904, and may have a value in the range 0.5-0.23 ohms.Capacitors1314 and1316 may have values of 0.1 μF and 2.2 μF, respectively.Inductor1322 may have a value of 150 μH,diode1312 may represent an ES2BA super-fast power diode, andLEDs1324 may be supplied by one or more of Nichia, Cree and Rebel.
• FIG. 14 shows AC dimmingsense filter1012 in exemplary detail.AC power910 is rectified by diodes1401(1) and1404(2) that form afull wave rectifier1402. Resistors1406,1408,1412,1416,1430,capacitors1410,1414,1418,1420, andamplifier1424, connected as shown inFIG. 14, cooperate to filter a rectified waveform fromrectifier1402 to produce dimmingindication signal1013. As described above, dimmingindication signal1013 has a DC component that is indicative of the AC dimming level applied to AC power910 (e.g., as applied byAC dimmer922,FIG. 9).Resistor1422 is optional and may be omitted.Capacitor1418 is optional and may be omitted.
• In one embodiment, diodes1401 are for example DFLS1100. Resistors1406,1408,1412,1416, and1430, may have values 294K, 42.2K, 107K, 25.5K, and 10K, respectively.Capacitors1410,1414, and1420, may have values 0.1 μF, 0.47 μF, and 0.22 μF, respectively.Amplifier1424 is for example an LM258D. Values foroptional resistor1422 andoptional capacitor1418 are selected based upon desired filtering characteristics of AC dimmingsense filter1012.
• FIG. 15 shows exemplary connectivity ofmicrocontroller1010,AC load1016, boostperformance sense1018, 0-10V input circuit1022, andPWM signal driver1014, ofFIG. 10.Microcontroller1010 is programmed with machine readable instructions that, when executed withinmicrocontroller1010, implement one or more algorithms foroperating system900.FIG. 15 shows exemplary detail ofPWM signal driver1014 formed ofresistors1506 and1510,capacitor1512, and adriver1508 that cooperate to generate PWMdimming control signal918 based upon PWMdimming control signal1011 frommicrocontroller1010. Resistors1506 and1510 may havevalues 10K and 100, respectively.Capacitor1512 may have a value of 0.1 μF.Microcontroller1010 is for example a Tiny24 by Atmel. Driver 1958 is for example a 74UHC1G125.
• With reference toFIG. 10,FIG. 15 also shows exemplary detail oftemperature sensor circuit1020 that includes athermistor1502 and aresistor1504 connected in series between secondoperational voltage934 andground rail914. A center connection betweenthermistor1502 andresistor1504 connects to an input (e.g., PA0) ofmicrocontroller1010, enabling one or more algorithms withinmicrocontroller1010 to determine temperature ofpower supply902. In one embodiment,Thermistor1502 may have a temperature coefficient of 100K, andresistor1504 may have a value of 10.0K.
• With reference toFIG. 10,FIG. 15 also shows boostperformance sense circuit1018 that convertsintegrator signal936 into a range suitable for input tomicrocontroller1010. Boostperformance sense circuit1018 includesresistors1520,1524,1526, and1528, and anamplifier1522.Boost performance signal1019 is output from boostperformance sense circuit1018 intomicrocontroller1010, wherein one or more algorithms may utilize boost performance information ofintegration signal936, at least in part, to control PWMdimming control signal1011. In one embodiment,resistors1520,1524,1526, and1528 may have values 51K, 10K, 174K, and 69.8K, respectively, andamplifier1522 is for example an LM258D.
• With reference toFIGS. 9 and 10,FIG. 15 also showsAC load circuit1016 that is controlled bymicrocontroller1010 to impart a load current onto rectifiedpower1205 to prevent erratic operation of AC dimmer922 at high dimming levels.AC load circuit1016 is formed ofresistors1530 and1534 and a metal oxide semiconductor field-effect transistor (MOSFET)1532. An output signal frommicrocontroller1010 turns onMOSFET1532 to draw current from rectifiedpower1205, throughresistor1530 andMOSFET1532 toground rail914, thereby increasing current throughAC dimmer922. In one embodiment,MOSFET1532 is for example a ZXMN4A06G from Zetex. Resistors1530 and1534 may have values 20 and 10K, respectively.
• With reference toFIG. 10,FIG. 15 also shows exemplary detail ofoptional input circuit1022.Input circuit1022 is formed withresistors1540,1542,1544, and1546, and acapacitor1548, as shown, and operates to bias, attenuate, and filterinput signal1032 for input tomicrocontroller1010. In one embodiment,resistors1540,1542,1544, and1546 may have values 12.4K, 665K, 49.9K, and 332K, respectively, andcapacitor1548 may have a value of 0.1 μF.
• FIG. 16 is a flowchart illustrating oneexemplary method1600 implemented withinmicrocontroller1010 ofFIG. 10, for example as an algorithm for controllingPWM dimming signal918. Instep1602, a temperature sense signal is read and a temperature of the power supply is determined. In one example ofstep1602,microcontroller1010 reads a temperature value fromtemperature circuit1020 and determines a current temperature ofpower supply902.Step1604 is a decision. If instep1604, the temperature determined instep1602 is greater than a maximum operational temperature ofpower supply902,method1600 continues withstep1606; otherwise,method1600 continues withstep1608. Instep1606, a required dimming level is set to 80%. In one example ofstep1606,microcontroller1010 sets an internal memory location to a value representative of 80% dimming level.Method1600 then proceeds withstep1618.
• Instep1608, the AC dimming indication signal is read. In one example ofstep1608,microcontroller1010 samples and convertsAC dimming signal1013 into a digital value. Instep1610, a required dimming level is calculated based upon the digital value ofstep1608. In one example ofstep1610,microcontroller1010 utilizes a formula for converting the digital value generated instep1608 into a value representative of the required dimming level. Instep1612, a boost performance sense signal is read and boost circuit performance is determined. In one example ofstep1612,microcontroller1010 samples and converts theoutput1019 of boostperformance sense circuit1018 into a digital value and utilizes a formula for calculating a performance factor ofboost circuit1004.Step1614 is a decision. If, instep1614, boost performance is below a minimum threshold,method1600 continues withstep1616; otherwise,method1600 continues withstep1618.
• Instep1616, the required dimming level ofstep1610 is adjusted based upon the determined boost circuit performance ofstep1612. In one example ofstep1616,microcontroller1010 increases the required dimming level if the determined boost performance indicated that the dimming level is being reduced too quickly. Instep1618, the PWM dimming signal mark to space ratio is set based upon the required dimming level. In one example ofstep1618,microcontroller1010 configures an internal PWM signal generator to generate a PWM signal for input toPWM driver circuit1506.
• Steps1602 through1618 repeat continuously to set dimming level oflighting fixtures904 based upon determined AC dimming level ofAC power910. Ordering of steps withinmethod1600 may change without departing from the scope hereof. For example,step1608 may be performed prior toconditional step1604.
• ConsideringFIG. 9 makes it clear that implementing power and control functions bypower supply902 inbus911 to serve any number oflighting fixtures904, enables modular LED light fixture configurations and manufacturing flexibility that are advantageous to both manufacturers and users of LED-based lighting products. For example,power supply902 may be regarded as a power supply subsystem that can supply power and control to one ormany lighting fixtures904.Lighting fixtures904 may vary greatly in shape, size, light output and spectral properties (e.g., as determined by selection ofLEDs1324,FIG. 13) while remaining compatible withpower supply902. In certain embodiments,bus911 may be implemented in the form of one or more connectorized cables connectingpower supply904 andlighting fixtures904 manufactured as physically discrete subsystems. In certain other embodiments,power supplies902 andlighting fixtures904 may be physically integrated into single finished products, but the manufacturing thereof may be staged independently (e.g., power supply subsystems may be built independently of lighting fixtures and the two may be integrated later at a final assembly stage).
• To a consumer, this means thatlighting system900 may be manufactured, sold and installed modularly. That is, the consumer can purchase and install onepower supply902, a number, type and position oflighting fixtures904, and appropriate cabling to implementbus911, for the consumer's desired application.Lighting fixtures904 can be swapped in and out forother lighting fixtures904, for example to modify power or spectral properties of the installation to suit changing needs or to replace alighting fixture904 that does not operate correctly.
• To a manufacturer, this means that power supplies902 may be mass manufactured, possibly ahead of specific orders and at low cost, while lightingfixtures904 can be manufactured more to order, to meet individual demands for fixtures of specific shapes, sizes, light outputs and spectral properties. Furthermore,lighting fixtures904 can be partially manufactured up to the point where they are populated with LEDs, so that when a customer order is placed and the LEDs for the order are stocked, the LEDs can be added tolighting fixtures904. This is similar to typical current practice wherein nearly finished LED-based lighting products can be staged without LEDs, except that when the lighting fixtures and power supply subsystems are manufactured separately, the inventory of power supply subsystems need not be “tied up,” that is, committed to specific lighting products, until after the LEDs are added to lighting fixtures.
• FIG. 17 is a flowchart of amethod1700 of manufacturing LED-based lighting products. Afirst step1702 manufactures power supply subsystems. An example ofstep1702 is manufacturing power supply902 (seeFIG. 9 for examples of items referred to throughout FIG.17). Anoptional step1704 manufactures cabling for connecting among power supply subsystems and lighting fixtures. An example ofstep1704 is manufacturing cabling that implementsbus911.
• Separately fromsteps1702 and1704, anoptional step1706 manufactures lighting fixtures without populating the fixtures with LEDs. An example ofstep1706 is manufacturinglighting fixtures904 without populating the LEDs on the fixtures. Other components of the lighting fixtures (e.g., components such ascontroller1302,capacitors1314 and1316,diodes1312 and1320,transistor1308,inductor1322 andresistors1304,1306 and1308, seeFIG. 13) may be added to the boards instep1706, or may be added when the LEDs are later attached instep1712, below. It is contemplated thatsteps1702,1704,1706 and1712, below, may be performed in the same manufacturing facility or in different manufacturing facilities, as preferred by the manufacturer to take advantage of opportunities to reduce cost and/or utilize manufacturing resources. In particular, it may be advantageous for a manufacturer to performsteps17021704 and/or1706 at a low cost, high volume manufacturing facility (due to the relative stability of the designs) but performstep1712 at another facility that can adapt to the inventory management challenges of tracking LED batches, and/or batches of lighting fixtures with the LEDs physically committed to them (e.g., by soldering the LEDs to the fixtures).
• Acustomer order1708 triggers astep1710 of stocking LEDs for lighting products to fill the customer order. One example ofstep1710 is identifying a set ofLEDs1324 that are already in the lighting product manufacturer's inventory, to add to lighting fixtures904 (seeFIG. 13). Another example ofstep1710 is ordering the LEDs and awaiting their arrival.Step1712 manufactures lighting fixtures with the appropriate LEDs stocked instep1710. As noted above, an example ofstep1712 is buildinglighting fixtures904 from the component level; another example is simply adding LEDs stocked instep1710 to lighting fixtures that were manufactured without LEDs instep1706.
• Aftersteps1702,1712 andoptional step1704, and when modular systems are being built,method1700 proceeds to step1718 where sets of power supply subsystems, lighting fixtures and cabling are shipped. An end user can then assemble the power supply subsystems and the lighting fixtures, using the cabling, to form LED-based lighting products. Furthermore, it is contemplated that the modular nature of lighting products described herein will lead to cases where a manufacturer may sometimes manufacture and deliver power supply subsystems, lighting fixtures and/or cabling as independent products. An example ofstep1718 is shipping sets that include one ormore power supplies902,lighting fixtures904 and cabling that implementsbus911. When an integrated lighting product is being built,method1700 instead proceeds to step1714 that integrates the lighting fixtures with the power supply subsystems. An example ofstep1714 is integrating one ormore lighting fixtures904 with apower supply902. Astep1716 ships the integrated lighting products manufactured instep1714.
• Changes may be made in the above methods and systems without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.

Claims (19)

What is claimed is:

1. A power supply for powering one or more loads, comprising:

a boost circuit with power factor correction (PFC) that provides an operating voltage from an electrical power source;

a dimmer detection circuit that (a) determines a dimming level applied to the electrical power source and (b) generates a pulse width modulated (PWM) signal based upon the dimming level; and

one or more current control circuits, each current control circuit being (c) associated with each of the one or more loads, and (d) coupled in series with the operating voltage, its associated load, and a ground of the power supply, so as to control a current through its associated load in response to the PWM signal.

2. The power supply ofclaim 1, the dimmer detection circuit comprising a microcontroller that (e) evaluates a waveform of the electrical power source to determine the dimming level applied by a dimming device connected to the electrical power source, and (f) generates the PWM signal based upon the dimming level.

3. The power supply ofclaim 2, the dimmer detection circuit further comprising an analog filter that filters the electrical signal source to provide an analog signal indicative of the dimming level, the microcontroller evaluating a digitized representation of the analog signal.

4. The power supply ofclaim 3, further comprising a switchable load under control of the microcontroller for drawing additional current through the dimming device when the dimming level is greater than a defined threshold, to prevent erratic operation of the dimming device.

5. The power supply ofclaim 2, the microcontroller delaying initiation of the PWM signal to allow the boost circuit to stabilize the operating voltage upon start-up of the power supply with the load connected.

6. The power supply ofclaim 1, each of the current control circuits configured to control the current through the load between a maximum current and no current.

7. The power supply ofclaim 1, the operating voltage being substantially 48V DC with respect to the ground.

8. The power supply ofclaim 1, each of the one or more loads comprising one or more light emitting diodes.

9. A method for driving at least one load using a boost circuit with power factor correction (PFC), a dimmer detection circuit, and a current control circuit, comprising:

receiving electrical power at the boost circuit;

generating an operating voltage within the boost circuit from the electrical power;

determining a dimming level within the dimmer detection circuit based upon a waveform of the electrical power;

generating, within the dimmer detection circuit, a pulse width modulated (PWM) signal indicative of the dimming level; and

controlling the current through the load using a switch of the current control circuit that is connected in series with the load, the switch being controlled based upon the PWM signal.

10. A method for manufacturing LED-based lighting products, comprising:

manufacturing power supply subsystems for the lighting products;

receiving a customer order for the lighting products, the customer order including an LED specification;

stocking LEDs to match the LED specification;

manufacturing LED-based lighting fixtures that utilize the LEDs; and

integrating the power supply subsystems with the LED-based lighting fixtures to form the lighting products.

11. The method ofclaim 10, further comprising manufacturing the LED-based lighting fixtures without LEDs before receiving the customer order, and wherein manufacturing the LED-based lighting fixtures that utilize the LEDs comprises adding at least the LEDs to the LED-based lighting fixtures.

12. The method ofclaim 10, further comprising manufacturing the power supply subsystems before receiving the customer order.

13. The method ofclaim 10, wherein manufacturing the power supply subsystems comprises manufacturing the power supply subsystems to include a bus output that includes at least power, ground and a dimming signal, and integrating comprises connecting the bus outputs from the power supply subsystems to the LED-based lighting fixtures.

14. The method ofclaim 13, wherein manufacturing the LED-based lighting fixtures comprises manufacturing the LED-based lighting fixtures to provide a pass-through connection for the bus output.

15. A method for manufacturing LED-based lighting products, comprising:

manufacturing power supply subsystems for the lighting products;

manufacturing cabling operable to connect the power supply subsystems with LED-based lighting fixtures;

receiving a customer order for the lighting products, the customer order including an LED specification;

stocking LEDs to match the LED specification;

manufacturing the LED-based lighting fixtures with the LEDs; and

shipping sets of the power supply subsystems, the cabling and the LED-based lighting fixtures to fill the customer order.

16. The method ofclaim 15, further comprising manufacturing the LED-based lighting fixtures without the LEDs before receiving the customer order, and wherein manufacturing the LED-based lighting fixtures with the LEDs comprises adding at least the LEDs to the lighting fixtures.

17. The method ofclaim 15, further comprising manufacturing the power supply subsystems before receiving the customer order.

18. The method ofclaim 15, wherein manufacturing the power supply subsystems comprises manufacturing the power supply subsystems to include a bus output that includes at least power, ground and a dimming signal, and manufacturing the cabling comprises manufacturing cabling operable to connect the bus output from one of the power supply subsystems to one or more of the LED-based lighting fixtures.

19. The method ofclaim 18, wherein manufacturing the LED-based lighting fixtures comprises manufacturing each of the LED-based lighting fixtures to provide a pass-through connection for the bus output.

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