US20160105936A1 - Ripple reduction in light emitting diode (led)-based light bulb through increased ripple on an energy storage capacitor - Google Patents
Ripple reduction in light emitting diode (led)-based light bulb through increased ripple on an energy storage capacitor Download PDFInfo
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- US20160105936A1 US20160105936A1 US14/509,660 US201414509660A US2016105936A1 US 20160105936 A1 US20160105936 A1 US 20160105936A1 US 201414509660 A US201414509660 A US 201414509660A US 2016105936 A1 US2016105936 A1 US 2016105936A1
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
- H05B47/10—Controlling the light source
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- H05B33/0803—
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
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- H05B37/02—
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/36—Circuits for reducing or suppressing harmonics, ripples or electromagnetic interferences [EMI]
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
- H05B45/3725—Switched mode power supply [SMPS]
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
- H05B45/3725—Switched mode power supply [SMPS]
- H05B45/375—Switched mode power supply [SMPS] using buck topology
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
- H05B45/3725—Switched mode power supply [SMPS]
- H05B45/382—Switched mode power supply [SMPS] with galvanic isolation between input and output
Definitions
- the instant disclosure relates to lighting circuits. More specifically, this disclosure relates to power supply circuitry for lighting circuits.
- Incandescent light bulbs include a metal filament. When electricity is applied to the metal filament, the metal filament heats and glows, radiating light into the surrounding area.
- the metal filament of conventional incandescent light bulbs generally has no specific power requirements. That is, any voltage and any current may be applied to the metal filament because the metal filament is a passive device. Although the voltage and current need to be sufficient to heat the metal filament to a glowing state, any other characteristics of the delivered energy to the metal filament do not affect operation of the incandescent light bulb. Thus, conventional line voltages in most residences and commercial buildings are sufficient for operation of the incandescent bulb. However, incandescent bulbs are not very efficient in conversion of energy to light, and thus waste energy.
- LED-based bulb One alternative lighting device with better efficiency is a light-emitting diode based bulb (LED-based bulb).
- the LEDs in the bulb consume energy from a line input source and convert the energy to light through photoemission.
- the LEDs unlike the metal filament, are not a passive component. Whereas the metal filament presents a nearly constant resistance to the line voltage source and can operate from AC voltages, LEDs are DC devices that need to have a controlled supply current.
- the controlled supply current is conventionally supplied by one or more power stages placed between the LEDs and the line voltage source.
- the power stages convert energy from the line voltage source to an appropriate input for the LEDs.
- the power stages also regulate the conversion of energy from the line voltage to the LEDs by regulating current through the LEDs because the emitted light is proportional to the current.
- Line voltage sources are generally alternating current (AC) waveforms. Because the voltage at the line source varies with time, the energy available to the LED-based bulb also varies over time. Without control over the conversion of energy within the LED-based bulb, the light output of the LED-based bulb would ripple over time along with the variations at the line voltage source.
- AC alternating current
- FIG. 1 is a circuit schematic illustrating a conventional two-stage, line-operated lamp circuit.
- a line voltage input node 102 is coupled to rectifiers 110 , which convert alternating current (AC) at input node 102 to direct current (DC) for output to a first stage DC-DC converter 112 .
- First stage 112 delivers a peak power to capacitor 114 of approximately double the average power consumed by light-emitting diodes (LEDs) 104 .
- a second stage DC-DC converter 116 consumes energy stored in the capacitor 114 and generates a constant current to drive the LEDs 104 .
- the circuit 100 provides a constant current with little ripple to the LEDs 104
- the circuit 100 includes two power converters, which increases the final cost of an LED-based bulb containing the circuit 100 .
- FIG. 2 is a circuit schematic illustrating another conventional line-operated lamp circuit with a single stage.
- a circuit 200 receives line voltage input at node 102 , which is provided to rectifier 110 .
- the DC output of the rectifier 110 is provided to capacitor 114 in parallel with transformer 212 and switch 216 .
- the capacitor 114 is a relatively small capacitor, such as 10-500 nanoFarads.
- the transformer 212 delivers energy from the rectifier 110 to the capacitor 214 and isolates capacitor 214 from the rectifier 110 .
- the capacitor 214 stores energy during peaks in the output of rectifier 110 and discharges energy during the troughs in the output of rectifier 110 to LEDs 104 .
- the LEDs 104 have small resistances to improve the efficiency of conversion of energy to light.
- the capacitor 214 must have a large capacitance.
- the physical size of capacitor 214 increases proportional to capacitance.
- the circuit 200 can become costly to manufacture and occupy too much space when capacitor 214 is large.
- the capacitor 214 is generally decreased in size, but the size reduction results in larger ripples in current through the LEDs 104 , and consequently ripples in the brightness of light output by the LEDs 104 .
- the LEDs 104 have a minimum required voltage, the forward bias voltage, in order to maintain the generation of light. Because the capacitor 214 acts as the energy supply for maintaining the forward bias voltage, the capacitor 214 must be a relatively large capacitor 214 . Additionally, other characteristics of the LEDs 104 place requirements on the size of the capacitor 214 in the design of FIG. 2 based on, for example, the non-linearity of the LEDs 104 . Although the solution of FIG. 2 resolves the problem of too much ripple in the output light, the circuit 100 is too costly to implement in low-cost devices, such as low-cost consumer light bulbs.
- Output ripple from a LED-based light bulb may be reduced through the use of a two-stage power converter with reduced cost by increasing a voltage ripple on a storage capacitor to decrease current ripple in the LEDs.
- By allowing an increased ripple voltage on the capacitor more of the energy storage potential of the capacitor may be utilized for generating light at the LEDs.
- the required forward bias voltage of the LEDs places a required minimum stored charge on the capacitor, which significantly reduces the available energy in the capacitor.
- the required forward bias voltage is 27 Volts and the capacitor is charged to 29 Volts
- the only energy available in the capacitor is that which when consumed does not reduce the capacitor below 27 Volts.
- Increasing a ripple on the capacitor above 29 Volts may unlock more energy storage potential of the capacitor.
- the second stage power converter may be manufactured at lower cost than in conventional two-stage converters.
- the increased voltage ripple on the capacitor may be obtained by a controller coupled to a switch in series with the LEDs. The controller may adjust a duty cycle of the switch, but maintain an approximately constant average duty cycle over at least a half of a cycle of the line input voltage.
- an apparatus may include a line voltage input node configured to receive a line voltage input; a rectifier coupled to the line voltage input node; a first switching stage coupled to the rectifier and configured to regulate a current to an intermediate node; a capacitor coupled to the intermediate node; a second switching stage coupled to the intermediate node and configured to provide an approximately constant ratio of input to output current; and/or a first controller coupled to the first switching stage and configured to regulate the first switching stage to maintain an approximately average current out of the first switching stage and into the intermediate node, the average current being averaged over each half line cycle of the input line voltage.
- the second switching stage may include a switch configured in series with a lighting load; the second switching stage may include a second controller coupled to the switch; the lighting load may include one or more light emitting diodes (LEDs); the controller may be integrated into a printed circuit board (PCB); the first switching stage may be integrated into a second printed circuit board (PCB); the second controller may be configured to operate the second switching stage at approximately a constant average duty cycle over a period of at least one half of a cycle of the line voltage input; the second controller may be configured to operate the switch to control a ripple on the capacitor to reduce a ripple through the lighting load; the second controller may be configured to operate the switch to control a voltage ripple on the capacitor to reduce a current ripple through the lighting load; the second controller may be configured to monitor a voltage across the capacitor; the second controller may be configured to reduce a power usage of the lighting load during a peak of the monitored voltage to allow the capacitor to charge; the second controller may be configured to reduce a duty cycle of the switch to reduce the power usage of the lighting
- a method may include regulating a current to an intermediate node in a first switching stage of a lamp to maintain an approximately average current for each half line cycle of an input line voltage; delivering current from the intermediate node to a second switching stage of the lamp; and/or regulating a ripple in an energy storage capacitor of the second switching stage of the lamp to provide an approximately constant ratio of input to output current.
- the approximately constant ratio may be greater than one; and/or the regulated ripple may be a regulated voltage ripple.
- the method may also include monitoring a voltage across the energy storage capacitor; reducing an output current during a peak of the monitored voltage to allow the energy storage capacitor to charge; the step of delivering current from the intermediate node to the second switching stage may include galvanically isolating the second switching stage from the first switching stage; the step of regulating a voltage ripple may include regulating an output current to have a current ripple less than approximately 20%; rising regulating a current through one or more light emitting diodes (LEDs) as a value approximately equal to the product of the average current from the first switching stage and the ratio of the second switching stage; and/or the step of regulating the current may include maintaining an approximately average current based, at least in part, on a dimmer setting for the lamp.
- LEDs light emitting diodes
- an apparatus may include a first printed circuit board (PCB) and a second printed circuit board (PCB) galvanically isolated from the first printed circuit board (PCB).
- the first PCB may include a line voltage input node configured to receive a line voltage input; a rectifier coupled to the line voltage input node; a first switching stage coupled to the rectifier and configured to maintain an approximately average current for each one half of a cycle of the input live voltage; and/or a transformer coupled to the first switching stage.
- the second PCB may include a lighting output node configured to provide an output current; a second switching stage coupled to the transformer to receive an input current from the first printed circuit board (PCB) and configured to provide an approximately constant ratio of input current to output current; and/or a controller coupled to the second switching stage and configured to operate the second switching stage at approximately a constant average duty cycle over a period of at least one half of a cycle of the line voltage input.
- the apparatus may also include one or more light emitting diodes (LEDs) coupled to the lighting output node.
- LEDs light emitting diodes
- the second switching stage of the second printed circuit board may include an energy storage capacitor; the controller of the second switching stage may be configured to control a voltage ripple on the energy storage capacitor to reduce a current ripple at the lighting output node; and/or the second switching stage of the second printed circuit board (PCB) may be coupled to the first switching stage of the first printed circuit board (PCB) by two wires.
- FIG. 1 is a circuit schematic illustrating a conventional two-stage, line-operated lamp circuit.
- FIG. 2 is a circuit schematic illustrating another conventional line-operated lamp circuit with a single stage.
- FIG. 3 is a circuit schematic illustrating a two-stage lamp circuit with controllable voltage ripple on a storage capacitor according to one embodiment of the disclosure.
- FIG. 4 are graphs illustrating operation of the controller maintaining an approximately constant average current according to one embodiment of the disclosure.
- FIG. 5 are graphs illustrating operation of a power converter for a LED-based light bulb over a cycle of a line voltage source according to one embodiment of the disclosure.
- FIG. 6 is a flow chart illustrating a method of powering a LED-based bulb with a two stage power converter with an increased voltage ripple on a storage energy capacitor according to one embodiment of the disclosure.
- FIG. 7 is a circuit illustrating a second stage configuration to reduce current ripple through LEDs according to one embodiment of the disclosure.
- FIG. 8 is a flow chart illustrating a method of controlling a voltage ripple on an energy storage capacitor according to one embodiment of the disclosure.
- FIG. 3 is a circuit schematic illustrating a two-stage lamp circuit with controllable voltage ripple on a storage capacitor according to one embodiment of the disclosure.
- a circuit 300 may include a line voltage input node 302 coupled to a rectifier 312 .
- the rectifier 312 converts an alternating current (AC) input from line voltage V LINE to a direct current (DC) output for a first stage power converter 300 A.
- the capacitor 314 may filter the DC output of the rectifier 312 , such as to reduce electromagnetic interference (EMI).
- a transformer 320 may couple the DC output of the rectifier 312 to a second stage power converter 300 B.
- the power converter 300 A may operate at a different switching frequency than the power converter 300 B. In one embodiment, the switching frequency of 300 B is higher than that of converter 300 A.
- a switch 316 in series with one winding of the transformer 320 may be operated by a controller 318 to control delivery of current to an intermediate node 350 . Adjusting a duty cycle of the switch 316 from the controller 318 may change a level of average current output by the transformer 320 to the intermediate node 350 . In one embodiment, the controller 318 may adjust the duty cycle of the switch 316 to maintain an approximately average current for each half line cycle of the line voltage at input node 302 .
- Current from the intermediate node 350 may power the second stage power converter 300 B.
- current may flow through a diode 332 to charge a capacitor 334 .
- Current i 1 352 may flow from the intermediate node 350 and from charge stored on the capacitor 334 .
- the current i 1 352 continues as current i 2 354 to generate an output voltage V LED for LEDs 342 .
- the current through the LEDs 342 may also flow through inductor 336 .
- a switch 338 coupled to the inductor 336 may determine how current flows from the inductor 336 .
- the switch 338 When the switch 338 is closed, some current may loop from the LEDs 342 to the capacitor 334 through the switch 338 .
- the switch 338 When the switch 338 is open, all current may loop from the LEDs 342 , through the inductor 336 to the diode 340 , and back through the LEDs 342 .
- a controller 348 may adjust a ratio of input current into the intermediate node 350 to output current through the LEDs 342 .
- the controller 348 may operate the switch 338 to provide an approximately constant ratio of input to output current.
- the controller 348 may maintain the approximately constant ratio, which may be greater than one, by monitoring a voltage at node 306 and/or a current at node 308 .
- the controller 348 may generate a control signal V CTRL,2 for operating the switch 338 based, in part, on the sensed voltage at node 306 and current at node 308 .
- the controller 348 may reduce a power usage of the lighting load during a peak of the monitored voltage to allow the capacitor 334 to charge.
- the controller 348 may charge the capacitor 334 when the monitored current at node 308 is below a threshold level.
- FIG. 4 are graphs illustrating operation of the controller maintaining an approximately constant average current according to one embodiment of the disclosure.
- a graph 402 illustrates a current i 2 354 through the LEDs 342 and the inductor 336 .
- a graph 404 illustrates the control signal V CTRL,2 for operating the switch 338 .
- the switch 338 is closed at time 412 , the current i 2 354 increases linearly as inductor 336 is charged.
- the controller 348 monitors current at node 308 . When the controller 348 determines the current i 2 354 reaches a certain threshold 432 , by detecting a proportionate amount of current at node 308 , the controller 348 may open the switch 338 .
- the switch 338 opens when the signal 404 goes to a low state.
- current 402 decreases as the inductor 338 is discharged through the LEDs 342 .
- the average current for i 1 352 over at least a half line cycle may be approximately equal to the current i 2 354 multiplied by a duty cycle, d, of the switch 338 (see “d” in FIG. 5 ).
- the timing of operation of the switch 338 may change to maintain an approximately constant average current through the LEDs 342 .
- the average current may be set by a ratio of time the switch is closed to time the switch is open.
- the time period 422 is a first time period during which the switch 338 is closed
- the time period 424 is a second time period during which the switch 338 is open.
- a ratio of the time period 422 to the time period 424 may be defined as a duty cycle of the switch 338 .
- the ratio may be adjusted by the controller 348 , which changes when the switch 338 closes with the control signal V CTRL,2 .
- FIG. 5 One example of this changing duty cycle over a full cycle of the line voltage is shown in FIG. 5 .
- FIG. 5 are graphs illustrating operation of a power converter for a LED-based light bulb over a cycle of a line voltage source according to one embodiment of the disclosure.
- a graph 502 illustrates a rectified voltage V RECT output by the rectifier 312 .
- the rectified voltage 502 follows the alternating current (AC) input at input node 302 .
- Graph 504 shows the power transfer from the line voltage source to the lamp circuit.
- Graph 506 shows a voltage V C3 across capacitor 334 .
- Graph 508 shows a duty cycle d of the switch 338 set by the controller 348 .
- the line cycle begins and the rectified voltage V RECT of graph 502 increases with the line voltage.
- the duty cycle of graph 508 may be at a maximum, such as at a duty cycle of 1.0.
- a duty cycle of 1.0 allows a maximum amount of energy to be stored from the line voltage source in capacitor 334 .
- the line voltage source, and consequently the rectified voltage V RECT of graph 502 decreases into a trough. Less energy is available during this decline and in the trough.
- the controller 348 may decrease the duty cycle shown in graph 508 .
- the duty cycle may be adjusted by the controller 348 while maintaining an average duty cycle.
- the duty cycle may vary from 0.9-1.0 and have an average value of 0.95.
- the average current through the LEDs 342 may be determined as the average current provided by transformer 320 divided by the average duty cycle.
- the controller 318 may be used to adjust a current through the LEDs 342 .
- the controller 318 may adjust a duty cycle of the switch 316 to adjust transfer of power from the first stage 300 A to the second stage 300 B.
- the controller 318 and the controller 348 may be independent controllers.
- the controller 348 and the second stage 300 B may be added to a power converter having the first stage 300 A.
- the second stage 300 B may thus be connected through only two wires to transformer 320 .
- a LED-based light bulb constructed with circuit 300 of FIG. 3 may include diode 332 , inductor 336 , switch 338 , and controller 348 integrated into a light engine board along with LEDs 342 .
- the controller 318 and the controller 348 may be integrated into a single controller.
- the circuit 300 of FIG. 3 may allow construction of a lamp circuit for an LED-based bulb with a reduced current ripple in the LEDs 342 similar to that achieved with prior art two-stage power converters, but with a reduced cost similar to that achieved with prior art one-stage power converters.
- the second stage 300 B of circuit 300 may be manufactured at lower cost than a conventional second stage power converter.
- Current ripple through the LEDs 342 may be reduced by controlling a duty cycle of the switch 338 from the controller 348 to allow a higher voltage ripple on capacitor 334 . In one embodiment, current ripple may be reduced below 20% for ideal light generation from LEDs 342 .
- a higher voltage ripple on the capacitor 334 may allow better utilization of the energy storage capacity of the capacitor 334 , and thus may allow a smaller capacitor 334 to be used in the circuit 300 .
- An increase of approximately double the voltage ripple on the energy storage capacitor may allow a reduction of size of the capacitor by half. Smaller capacitors have a reduced cost and allow the LED-based light bulb to be constructed in a smaller physical volume.
- C is a capacitance of capacitor 334 and V is a voltage across the capacitor 334 .
- a larger voltage ripple may increase the energy stored by the capacitor 334 by increasing V.
- a larger energy store within the circuit 300 may allow a lower ripple of current through the LEDs 342 .
- the available energy in the capacitor 334 is the difference between the energy stored by the capacitor at 29 Volts and the energy stored by the capacitor at 27 Volts. Energy stored in the capacitor when the voltage decreases below 27 Volts is not available because the LEDs 342 do not operate below 27 Volts.
- the energy accessible by the LEDs 342 in the capacitor at a 2 Volt ripple is
- C is the capacitance of capacitor 334 .
- a ripple increase of 2 Volts on the capacitor 334 produces an approximate doubling of the usable energy storage of the capacitor 334 for the same capacitance.
- the capacitance, and therefore size, of the capacitor 334 may be reduced while maintaining a certain level of energy storage in the circuit 300 .
- controller 348 may operate the switch 338 at a high switching frequency and a high duty cycle to allow the size of inductor 336 to be reduced. Reducing the size of the inductor 336 further allows a reduction in cost of the circuit 300 and a reduction in the physical volume of an LED-based light bulb.
- FIG. 6 is a flow chart illustrating a method of powering a LED-based bulb with a two stage power converter with an increased voltage ripple on a storage capacitor according to one embodiment of the disclosure.
- a method 600 begins at block 602 with regulating a current to an intermediate node in a first switching stage to maintain an approximately average current for each half-line cycle of an input line voltage.
- current may be delivered from the intermediate node to a second switching stage, including an energy storage capacitor.
- a voltage ripple in the energy storage capacitor may be regulated to provide an approximately constant ratio of input to output current at the second switching stage.
- a controller may monitor a voltage across the energy storage capacitor, such as capacitor 334 , and operate a switch, such as switch 338 , to regulate a ripple on the capacitor.
- the output current of the second switching stage may be provided to LEDs.
- a controller for regulating voltage ripple on a storage capacitor may be implemented in other power converter configurations.
- a second stage may be modified to include a capability to short some of the diodes during a trough of the line voltage.
- FIG. 7 is a circuit illustrating a second stage configuration to reduce current ripple through LEDs according to one embodiment of the disclosure.
- a circuit 700 may include a transformer 720 coupled by one winding to a PFC single stage (not shown).
- a second winding of the transformer 720 may couple to intermediate node 750 and to the capacitor 734 .
- a controller 748 may be coupled to a switch 738 , which is coupled to inductor 736 .
- the capacitor 734 may store energy when power transfer from a line voltage source in the PFC single stage is high, such as during peaks in the source waveform.
- the controller 748 may operate the switch 738 to buck capacitor 734 to provide energy to the inductor 736 , and thus light emitting diodes (LEDs).
- Energy provided by the capacitor 734 may reduce current ripples through the light emitting diodes (LEDs), and consequently reduce variations in light output from the LED-based light bulb.
- FIG. 8 is a flow chart illustrating a method of controlling a voltage ripple on an energy storage capacitor according to one embodiment of the disclosure.
- a method 800 begins at block 802 with detecting a transient in the voltage across the link capacitor.
- a voltage ripple target is set for the link capacitor to a first value, which may be a maximum value.
- the controller may monitor the link capacitor voltage during at least a half of a line cycle.
- the method 800 may wait at block 808 .
- the method 800 proceeds to block 810 .
- the link capacitor maximum voltage V LINK,MAX may be compared to the result of a target voltage V TGT with a scaling factor a, where the product of a*V TGT is a predetermined threshold of maximum allowable voltage on the capacitor that may be set to a value approximately equal to a rated maximum voltage for the capacitor. If the V LINK,MAX value is less than the result, then the ripple on the link capacitor may be decreased at block 812 . If the V LINK,MAX value is not less than the result, then the method 800 proceeds to block 814 .
- the V LINK,MAX value is compared to the result to determine if the V LINK,MAX value is greater than the result. If so, then the voltage ripple on the link capacitor is increased at block 816 . If not, then the method 800 returns to block 808 . The method 800 may continue through the blocks 808 , 810 , and 814 , for the duration of the half of a line cycle. If the link capacitor voltage reaches V TGT , which is larger than a*V TGT prior to a disconnect time of a dimmer providing current to the LED-based bulb, then the output may be immediately shut off until the disconnect time.
- V TGT which is larger than a*V TGT prior to a disconnect time of a dimmer providing current to the LED-based bulb
- This method may allow monitoring of a maximum voltage on the capacitor over a half line cycle and increasing or decreasing the ripple on the capacitor based on the monitored maximum voltage. This method may further optimize the output ripple allowed on the capacitor and further improve the amount of energy storage available in the capacitor for use by the LEDs.
- the functions described above, such as illustrated in FIG. 6 and FIG. 8 may be stored as one or more instructions or code on a computer-readable medium. Examples include non-transitory computer-readable media encoded with a data structure and computer-readable media encoded with a computer program.
- Computer-readable media includes physical computer storage media. A storage medium may be any available medium that can be accessed by a computer.
- such computer-readable media can comprise random access memory (RAM), read-only memory (ROM), electronically-erasable programmable read-only memory (EEPROM), compact disc-read-only memory (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.
- Disk and disc includes compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and blu-ray discs. Generally, disks reproduce data magnetically, and discs reproduce data optically. Combinations of the above should also be included within the scope of computer-readable media.
- instructions and/or data may be provided as signals on transmission media included in a communication apparatus.
- a communication apparatus may include a transceiver having signals indicative of instructions and data. The instructions and data are configured to cause one or more processors to implement the functions outlined in the claims.
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Abstract
Description
- The instant disclosure relates to lighting circuits. More specifically, this disclosure relates to power supply circuitry for lighting circuits.
- Alternative lighting devices to replace incandescent light bulbs differ from incandescent light bulbs in the manner that energy is converted to light. Incandescent light bulbs include a metal filament. When electricity is applied to the metal filament, the metal filament heats and glows, radiating light into the surrounding area. The metal filament of conventional incandescent light bulbs generally has no specific power requirements. That is, any voltage and any current may be applied to the metal filament because the metal filament is a passive device. Although the voltage and current need to be sufficient to heat the metal filament to a glowing state, any other characteristics of the delivered energy to the metal filament do not affect operation of the incandescent light bulb. Thus, conventional line voltages in most residences and commercial buildings are sufficient for operation of the incandescent bulb. However, incandescent bulbs are not very efficient in conversion of energy to light, and thus waste energy.
- One alternative lighting device with better efficiency is a light-emitting diode based bulb (LED-based bulb). The LEDs in the bulb consume energy from a line input source and convert the energy to light through photoemission. However, the LEDs, unlike the metal filament, are not a passive component. Whereas the metal filament presents a nearly constant resistance to the line voltage source and can operate from AC voltages, LEDs are DC devices that need to have a controlled supply current. The controlled supply current is conventionally supplied by one or more power stages placed between the LEDs and the line voltage source. The power stages convert energy from the line voltage source to an appropriate input for the LEDs. The power stages also regulate the conversion of energy from the line voltage to the LEDs by regulating current through the LEDs because the emitted light is proportional to the current.
- Line voltage sources are generally alternating current (AC) waveforms. Because the voltage at the line source varies with time, the energy available to the LED-based bulb also varies over time. Without control over the conversion of energy within the LED-based bulb, the light output of the LED-based bulb would ripple over time along with the variations at the line voltage source. One conventional lamp circuit for controlling a LED-based bulb to reduce variations is shown in
FIG. 1 . -
FIG. 1 is a circuit schematic illustrating a conventional two-stage, line-operated lamp circuit. Incircuit 100, a linevoltage input node 102 is coupled torectifiers 110, which convert alternating current (AC) atinput node 102 to direct current (DC) for output to a first stage DC-DC converter 112.First stage 112 delivers a peak power tocapacitor 114 of approximately double the average power consumed by light-emitting diodes (LEDs) 104. A second stage DC-DC converter 116 consumes energy stored in thecapacitor 114 and generates a constant current to drive theLEDs 104. Although thecircuit 100 provides a constant current with little ripple to theLEDs 104, thecircuit 100 includes two power converters, which increases the final cost of an LED-based bulb containing thecircuit 100. - An alternate lamp circuit with only a single power converter for performing a power factor correction (PFC) is shown in
FIG. 2 .FIG. 2 is a circuit schematic illustrating another conventional line-operated lamp circuit with a single stage. Acircuit 200 receives line voltage input atnode 102, which is provided to rectifier 110. The DC output of therectifier 110 is provided tocapacitor 114 in parallel withtransformer 212 andswitch 216. Thecapacitor 114 is a relatively small capacitor, such as 10-500 nanoFarads. Thetransformer 212 delivers energy from therectifier 110 to thecapacitor 214 andisolates capacitor 214 from therectifier 110. Thecapacitor 214 stores energy during peaks in the output ofrectifier 110 and discharges energy during the troughs in the output ofrectifier 110 toLEDs 104. TheLEDs 104 have small resistances to improve the efficiency of conversion of energy to light. Thus, to reduce ripple in the current atLEDs 104, thecapacitor 214 must have a large capacitance. The physical size ofcapacitor 214 increases proportional to capacitance. Thus, thecircuit 200 can become costly to manufacture and occupy too much space whencapacitor 214 is large. To reduce cost, thecapacitor 214 is generally decreased in size, but the size reduction results in larger ripples in current through theLEDs 104, and consequently ripples in the brightness of light output by theLEDs 104. Further, theLEDs 104 have a minimum required voltage, the forward bias voltage, in order to maintain the generation of light. Because thecapacitor 214 acts as the energy supply for maintaining the forward bias voltage, thecapacitor 214 must be a relativelylarge capacitor 214. Additionally, other characteristics of theLEDs 104 place requirements on the size of thecapacitor 214 in the design ofFIG. 2 based on, for example, the non-linearity of theLEDs 104. Although the solution ofFIG. 2 resolves the problem of too much ripple in the output light, thecircuit 100 is too costly to implement in low-cost devices, such as low-cost consumer light bulbs. - Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved lamp circuits particularly for LED-based light bulbs. Embodiments described here address certain shortcomings but not necessarily each and every one described here or known in the art.
- Output ripple from a LED-based light bulb may be reduced through the use of a two-stage power converter with reduced cost by increasing a voltage ripple on a storage capacitor to decrease current ripple in the LEDs. By allowing an increased ripple voltage on the capacitor, more of the energy storage potential of the capacitor may be utilized for generating light at the LEDs. For example, the required forward bias voltage of the LEDs places a required minimum stored charge on the capacitor, which significantly reduces the available energy in the capacitor. In one illustration of this restriction, when the required forward bias voltage is 27 Volts and the capacitor is charged to 29 Volts, the only energy available in the capacitor is that which when consumed does not reduce the capacitor below 27 Volts. Increasing a ripple on the capacitor above 29 Volts may unlock more energy storage potential of the capacitor. Because a larger amount of the energy storage potential of the capacitor may be utilized, a smaller capacitor may be used in the lamp circuit of the light bulb. The smaller capacitor allows for smaller lamp circuits and lower-cost lamp circuit to be implemented in LED-based light bulbs. Further, the second stage power converter may be manufactured at lower cost than in conventional two-stage converters. The increased voltage ripple on the capacitor may be obtained by a controller coupled to a switch in series with the LEDs. The controller may adjust a duty cycle of the switch, but maintain an approximately constant average duty cycle over at least a half of a cycle of the line input voltage.
- According to one embodiment, an apparatus may include a line voltage input node configured to receive a line voltage input; a rectifier coupled to the line voltage input node; a first switching stage coupled to the rectifier and configured to regulate a current to an intermediate node; a capacitor coupled to the intermediate node; a second switching stage coupled to the intermediate node and configured to provide an approximately constant ratio of input to output current; and/or a first controller coupled to the first switching stage and configured to regulate the first switching stage to maintain an approximately average current out of the first switching stage and into the intermediate node, the average current being averaged over each half line cycle of the input line voltage.
- In certain embodiments, the second switching stage may include a switch configured in series with a lighting load; the second switching stage may include a second controller coupled to the switch; the lighting load may include one or more light emitting diodes (LEDs); the controller may be integrated into a printed circuit board (PCB); the first switching stage may be integrated into a second printed circuit board (PCB); the second controller may be configured to operate the second switching stage at approximately a constant average duty cycle over a period of at least one half of a cycle of the line voltage input; the second controller may be configured to operate the switch to control a ripple on the capacitor to reduce a ripple through the lighting load; the second controller may be configured to operate the switch to control a voltage ripple on the capacitor to reduce a current ripple through the lighting load; the second controller may be configured to monitor a voltage across the capacitor; the second controller may be configured to reduce a power usage of the lighting load during a peak of the monitored voltage to allow the capacitor to charge; the second controller may be configured to reduce a duty cycle of the switch to reduce the power usage of the lighting load; the second controller may be configured to monitor a current through the lighting load; the second controller may be configured to charge the capacitor when the current through the lighting load is below a threshold; the first switching stage may be galvanically isolated from the second switching stage; the second switching stage may operate at a higher operating frequency than the first switching stage; the first controller may be configured to maintain an approximately average current based, at least in part, on a dimmer setting for the lighting load; and/or the first controller may be configured to regulate a current through the one or more light emitting diodes (LEDs) as a value approximately equal to the product of the average current from the first switching stage and the ratio of the second switching stage.
- According to another embodiment, a method may include regulating a current to an intermediate node in a first switching stage of a lamp to maintain an approximately average current for each half line cycle of an input line voltage; delivering current from the intermediate node to a second switching stage of the lamp; and/or regulating a ripple in an energy storage capacitor of the second switching stage of the lamp to provide an approximately constant ratio of input to output current. In certain embodiments, the approximately constant ratio may be greater than one; and/or the regulated ripple may be a regulated voltage ripple.
- In some embodiments, the method may also include monitoring a voltage across the energy storage capacitor; reducing an output current during a peak of the monitored voltage to allow the energy storage capacitor to charge; the step of delivering current from the intermediate node to the second switching stage may include galvanically isolating the second switching stage from the first switching stage; the step of regulating a voltage ripple may include regulating an output current to have a current ripple less than approximately 20%; rising regulating a current through one or more light emitting diodes (LEDs) as a value approximately equal to the product of the average current from the first switching stage and the ratio of the second switching stage; and/or the step of regulating the current may include maintaining an approximately average current based, at least in part, on a dimmer setting for the lamp.
- According to a further embodiment, an apparatus may include a first printed circuit board (PCB) and a second printed circuit board (PCB) galvanically isolated from the first printed circuit board (PCB). The first PCB may include a line voltage input node configured to receive a line voltage input; a rectifier coupled to the line voltage input node; a first switching stage coupled to the rectifier and configured to maintain an approximately average current for each one half of a cycle of the input live voltage; and/or a transformer coupled to the first switching stage. The second PCB may include a lighting output node configured to provide an output current; a second switching stage coupled to the transformer to receive an input current from the first printed circuit board (PCB) and configured to provide an approximately constant ratio of input current to output current; and/or a controller coupled to the second switching stage and configured to operate the second switching stage at approximately a constant average duty cycle over a period of at least one half of a cycle of the line voltage input. In some embodiments, the apparatus may also include one or more light emitting diodes (LEDs) coupled to the lighting output node.
- In certain embodiments, the second switching stage of the second printed circuit board (PCB) may include an energy storage capacitor; the controller of the second switching stage may be configured to control a voltage ripple on the energy storage capacitor to reduce a current ripple at the lighting output node; and/or the second switching stage of the second printed circuit board (PCB) may be coupled to the first switching stage of the first printed circuit board (PCB) by two wires.
- The foregoing has outlined rather broadly certain features and technical advantages of embodiments of the present invention in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those having ordinary skill in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same or similar purposes. It should also be realized by those having ordinary skill in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. Additional features will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended to limit the present invention.
- For a more complete understanding of the disclosed system and methods, reference is now made to the following descriptions taken in conjunction with the accompanying drawings.
-
FIG. 1 is a circuit schematic illustrating a conventional two-stage, line-operated lamp circuit. -
FIG. 2 is a circuit schematic illustrating another conventional line-operated lamp circuit with a single stage. -
FIG. 3 is a circuit schematic illustrating a two-stage lamp circuit with controllable voltage ripple on a storage capacitor according to one embodiment of the disclosure. -
FIG. 4 are graphs illustrating operation of the controller maintaining an approximately constant average current according to one embodiment of the disclosure. -
FIG. 5 are graphs illustrating operation of a power converter for a LED-based light bulb over a cycle of a line voltage source according to one embodiment of the disclosure. -
FIG. 6 is a flow chart illustrating a method of powering a LED-based bulb with a two stage power converter with an increased voltage ripple on a storage energy capacitor according to one embodiment of the disclosure. -
FIG. 7 is a circuit illustrating a second stage configuration to reduce current ripple through LEDs according to one embodiment of the disclosure. -
FIG. 8 is a flow chart illustrating a method of controlling a voltage ripple on an energy storage capacitor according to one embodiment of the disclosure. -
FIG. 3 is a circuit schematic illustrating a two-stage lamp circuit with controllable voltage ripple on a storage capacitor according to one embodiment of the disclosure. Acircuit 300 may include a linevoltage input node 302 coupled to arectifier 312. Therectifier 312 converts an alternating current (AC) input from line voltage VLINE to a direct current (DC) output for a firststage power converter 300A. Thecapacitor 314 may filter the DC output of therectifier 312, such as to reduce electromagnetic interference (EMI). Atransformer 320 may couple the DC output of therectifier 312 to a secondstage power converter 300B. Thepower converter 300A may operate at a different switching frequency than thepower converter 300B. In one embodiment, the switching frequency of 300B is higher than that ofconverter 300A. - A
switch 316 in series with one winding of thetransformer 320 may be operated by acontroller 318 to control delivery of current to anintermediate node 350. Adjusting a duty cycle of theswitch 316 from thecontroller 318 may change a level of average current output by thetransformer 320 to theintermediate node 350. In one embodiment, thecontroller 318 may adjust the duty cycle of theswitch 316 to maintain an approximately average current for each half line cycle of the line voltage atinput node 302. - Current from the
intermediate node 350 may power the secondstage power converter 300B. Inconverter 300B, current may flow through adiode 332 to charge acapacitor 334.Current i 1 352 may flow from theintermediate node 350 and from charge stored on thecapacitor 334. Thecurrent i 1 352 continues ascurrent i 2 354 to generate an output voltage VLED forLEDs 342. The current through theLEDs 342 may also flow throughinductor 336. - A
switch 338 coupled to theinductor 336 may determine how current flows from theinductor 336. When theswitch 338 is closed, some current may loop from theLEDs 342 to thecapacitor 334 through theswitch 338. When theswitch 338 is open, all current may loop from theLEDs 342, through theinductor 336 to thediode 340, and back through theLEDs 342. By operating theswitch 338, acontroller 348 may adjust a ratio of input current into theintermediate node 350 to output current through theLEDs 342. In one embodiment, thecontroller 348 may operate theswitch 338 to provide an approximately constant ratio of input to output current. Thecontroller 348 may maintain the approximately constant ratio, which may be greater than one, by monitoring a voltage atnode 306 and/or a current atnode 308. Thecontroller 348 may generate a control signal VCTRL,2 for operating theswitch 338 based, in part, on the sensed voltage atnode 306 and current atnode 308. For example, thecontroller 348 may reduce a power usage of the lighting load during a peak of the monitored voltage to allow thecapacitor 334 to charge. In another example, thecontroller 348 may charge thecapacitor 334 when the monitored current atnode 308 is below a threshold level. -
FIG. 4 are graphs illustrating operation of the controller maintaining an approximately constant average current according to one embodiment of the disclosure. Agraph 402 illustrates acurrent i 2 354 through theLEDs 342 and theinductor 336. Agraph 404 illustrates the control signal VCTRL,2 for operating theswitch 338. When theswitch 338 is closed attime 412, thecurrent i 2 354 increases linearly asinductor 336 is charged. Thecontroller 348 monitors current atnode 308. When thecontroller 348 determines thecurrent i 2 354 reaches acertain threshold 432, by detecting a proportionate amount of current atnode 308, thecontroller 348 may open theswitch 338. Attime 414, theswitch 338 opens when thesignal 404 goes to a low state. As a result, current 402 decreases as theinductor 338 is discharged through theLEDs 342. The average current for i1 352 over at least a half line cycle may be approximately equal to thecurrent i 2 354 multiplied by a duty cycle, d, of the switch 338 (see “d” inFIG. 5 ). - The timing of operation of the
switch 338 may change to maintain an approximately constant average current through theLEDs 342. The average current may be set by a ratio of time the switch is closed to time the switch is open. InFIG. 4 , thetime period 422 is a first time period during which theswitch 338 is closed, and thetime period 424 is a second time period during which theswitch 338 is open. A ratio of thetime period 422 to thetime period 424 may be defined as a duty cycle of theswitch 338. The ratio may be adjusted by thecontroller 348, which changes when theswitch 338 closes with the control signal VCTRL,2. One example of this changing duty cycle over a full cycle of the line voltage is shown inFIG. 5 . -
FIG. 5 are graphs illustrating operation of a power converter for a LED-based light bulb over a cycle of a line voltage source according to one embodiment of the disclosure. Agraph 502 illustrates a rectified voltage VRECT output by therectifier 312. The rectifiedvoltage 502 follows the alternating current (AC) input atinput node 302.Graph 504 shows the power transfer from the line voltage source to the lamp circuit.Graph 506 shows a voltage VC3 acrosscapacitor 334.Graph 508 shows a duty cycle d of theswitch 338 set by thecontroller 348. Attime 512, the line cycle begins and the rectified voltage VRECT ofgraph 502 increases with the line voltage. During this portion of the line cycle, the duty cycle ofgraph 508 may be at a maximum, such as at a duty cycle of 1.0. A duty cycle of 1.0 allows a maximum amount of energy to be stored from the line voltage source incapacitor 334. Attime 514, the line voltage source, and consequently the rectified voltage VRECT ofgraph 502, decreases into a trough. Less energy is available during this decline and in the trough. Thus, thecontroller 348 may decrease the duty cycle shown ingraph 508. - The duty cycle may be adjusted by the
controller 348 while maintaining an average duty cycle. In one embodiment, the duty cycle may vary from 0.9-1.0 and have an average value of 0.95. The average current through theLEDs 342 may be determined as the average current provided bytransformer 320 divided by the average duty cycle. When the average duty cycle is fixed by thecontroller 348, thecontroller 318 may be used to adjust a current through theLEDs 342. For example, thecontroller 318 may adjust a duty cycle of theswitch 316 to adjust transfer of power from thefirst stage 300A to thesecond stage 300B. - Referring to
FIG. 3 , thecontroller 318 and thecontroller 348 may be independent controllers. Thus, for example, thecontroller 348 and thesecond stage 300B may be added to a power converter having thefirst stage 300A. Thesecond stage 300B may thus be connected through only two wires totransformer 320. In one embodiment, a LED-based light bulb constructed withcircuit 300 ofFIG. 3 may includediode 332,inductor 336,switch 338, andcontroller 348 integrated into a light engine board along withLEDs 342. In another embodiment, thecontroller 318 and thecontroller 348 may be integrated into a single controller. - The
circuit 300 ofFIG. 3 may allow construction of a lamp circuit for an LED-based bulb with a reduced current ripple in theLEDs 342 similar to that achieved with prior art two-stage power converters, but with a reduced cost similar to that achieved with prior art one-stage power converters. In particular, thesecond stage 300B ofcircuit 300 may be manufactured at lower cost than a conventional second stage power converter. Current ripple through theLEDs 342 may be reduced by controlling a duty cycle of theswitch 338 from thecontroller 348 to allow a higher voltage ripple oncapacitor 334. In one embodiment, current ripple may be reduced below 20% for ideal light generation fromLEDs 342. A higher voltage ripple on thecapacitor 334 may allow better utilization of the energy storage capacity of thecapacitor 334, and thus may allow asmaller capacitor 334 to be used in thecircuit 300. An increase of approximately double the voltage ripple on the energy storage capacitor may allow a reduction of size of the capacitor by half. Smaller capacitors have a reduced cost and allow the LED-based light bulb to be constructed in a smaller physical volume. - Increasing the voltage ripple to allow use of a smaller capacitor is illustrated in the example below. If the
LEDs 342 operate at 27 Volts, then thecapacitor 334 must be maintained above 27 Volts for the LEDs to operate. Energy stored in a capacitor, E, may be calculated as -
- where C is a capacitance of
capacitor 334 and V is a voltage across thecapacitor 334. A larger voltage ripple may increase the energy stored by thecapacitor 334 by increasing V. A larger energy store within thecircuit 300 may allow a lower ripple of current through theLEDs 342. For example, when a voltage ripple of 2 Volts is allowed across thecapacitor 334, the available energy in thecapacitor 334 is the difference between the energy stored by the capacitor at 29 Volts and the energy stored by the capacitor at 27 Volts. Energy stored in the capacitor when the voltage decreases below 27 Volts is not available because theLEDs 342 do not operate below 27 Volts. Thus, the energy accessible by theLEDs 342 in the capacitor at a 2 Volt ripple is -
- where C is the capacitance of
capacitor 334. When a voltage ripple of 4 Volts is allowed across thecapacitor 334, the available energy in the capacitor is -
- where C is the capacitance of
capacitor 334. In this example, a ripple increase of 2 Volts on thecapacitor 334 produces an approximate doubling of the usable energy storage of thecapacitor 334 for the same capacitance. Thus, the capacitance, and therefore size, of thecapacitor 334 may be reduced while maintaining a certain level of energy storage in thecircuit 300. - Further, reductions in size may be achieved with the
controller 348. For example, thecontroller 348 may operate theswitch 338 at a high switching frequency and a high duty cycle to allow the size ofinductor 336 to be reduced. Reducing the size of theinductor 336 further allows a reduction in cost of thecircuit 300 and a reduction in the physical volume of an LED-based light bulb. - Operation of the
circuit 300 to deliver a nearly constant current toLEDs 342 is described inFIG. 6 .FIG. 6 is a flow chart illustrating a method of powering a LED-based bulb with a two stage power converter with an increased voltage ripple on a storage capacitor according to one embodiment of the disclosure. Amethod 600 begins atblock 602 with regulating a current to an intermediate node in a first switching stage to maintain an approximately average current for each half-line cycle of an input line voltage. Atblock 604, current may be delivered from the intermediate node to a second switching stage, including an energy storage capacitor. Atblock 606, a voltage ripple in the energy storage capacitor may be regulated to provide an approximately constant ratio of input to output current at the second switching stage. In one embodiment, a controller may monitor a voltage across the energy storage capacitor, such ascapacitor 334, and operate a switch, such asswitch 338, to regulate a ripple on the capacitor. The output current of the second switching stage may be provided to LEDs. By regulating the voltage ripple on the energy storage capacitor to increase accessibility of energy storage within thecircuit 300, the current ripple through theLEDs 342 may be reduced and a more constant light output from theLEDs 342 may be obtained. - A controller for regulating voltage ripple on a storage capacitor may be implemented in other power converter configurations. For example, a second stage may be modified to include a capability to short some of the diodes during a trough of the line voltage.
FIG. 7 is a circuit illustrating a second stage configuration to reduce current ripple through LEDs according to one embodiment of the disclosure. Acircuit 700 may include atransformer 720 coupled by one winding to a PFC single stage (not shown). A second winding of thetransformer 720 may couple tointermediate node 750 and to thecapacitor 734. Acontroller 748 may be coupled to aswitch 738, which is coupled toinductor 736. Thecapacitor 734 may store energy when power transfer from a line voltage source in the PFC single stage is high, such as during peaks in the source waveform. When the power transfer is decreasing or in a trough, thecontroller 748 may operate theswitch 738 to buckcapacitor 734 to provide energy to theinductor 736, and thus light emitting diodes (LEDs). Energy provided by thecapacitor 734 may reduce current ripples through the light emitting diodes (LEDs), and consequently reduce variations in light output from the LED-based light bulb. - The
controller 748 ofFIG. 7 or thecontroller 348 ofFIG. 3 may execute an algorithm for controlling a voltage ripple on theenergy storage capacitor 734 ofFIG. 7 and thecapacitor 334 ofFIG. 3 , or link capacitor.FIG. 8 is a flow chart illustrating a method of controlling a voltage ripple on an energy storage capacitor according to one embodiment of the disclosure. Amethod 800 begins atblock 802 with detecting a transient in the voltage across the link capacitor. Atblock 804, a voltage ripple target is set for the link capacitor to a first value, which may be a maximum value. Atblock 806, the controller may monitor the link capacitor voltage during at least a half of a line cycle. Atblock 808, it is determined whether the voltage ripple is zero. If so, themethod 800 may wait atblock 808. When the voltage ripple exists, themethod 800 proceeds to block 810. Atblock 810, the link capacitor maximum voltage VLINK,MAX may be compared to the result of a target voltage VTGT with a scaling factor a, where the product of a*VTGT is a predetermined threshold of maximum allowable voltage on the capacitor that may be set to a value approximately equal to a rated maximum voltage for the capacitor. If the VLINK,MAX value is less than the result, then the ripple on the link capacitor may be decreased atblock 812. If the VLINK,MAX value is not less than the result, then themethod 800 proceeds to block 814. Atblock 814, the VLINK,MAX value is compared to the result to determine if the VLINK,MAX value is greater than the result. If so, then the voltage ripple on the link capacitor is increased atblock 816. If not, then themethod 800 returns to block 808. Themethod 800 may continue through theblocks method 800 ofFIG. 8 may allow monitoring of a maximum voltage on the capacitor over a half line cycle and increasing or decreasing the ripple on the capacitor based on the monitored maximum voltage. This method may further optimize the output ripple allowed on the capacitor and further improve the amount of energy storage available in the capacitor for use by the LEDs. - If implemented in firmware and/or software, the functions described above, such as illustrated in
FIG. 6 andFIG. 8 , may be stored as one or more instructions or code on a computer-readable medium. Examples include non-transitory computer-readable media encoded with a data structure and computer-readable media encoded with a computer program. Computer-readable media includes physical computer storage media. A storage medium may be any available medium that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise random access memory (RAM), read-only memory (ROM), electronically-erasable programmable read-only memory (EEPROM), compact disc-read-only memory (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc includes compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and blu-ray discs. Generally, disks reproduce data magnetically, and discs reproduce data optically. Combinations of the above should also be included within the scope of computer-readable media. - In addition to storage on computer readable medium, instructions and/or data may be provided as signals on transmission media included in a communication apparatus. For example, a communication apparatus may include a transceiver having signals indicative of instructions and data. The instructions and data are configured to cause one or more processors to implement the functions outlined in the claims.
- Although the present disclosure and certain representative advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, techniques described above may also be applied to linear regulators, in which a drive current may equal an output current to LEDs. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
Claims (27)
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EP15797197.9A EP3205182A2 (en) | 2014-10-08 | 2015-10-08 | Ripple reduction in light emitting diode (led)-based light bulb through increased ripple on an energy storage capacitor |
CN201580054819.9A CN107113930B (en) | 2014-10-08 | 2015-10-08 | The ripple in the light bulb based on light emitting diode (LED) is reduced by increasing the ripple in energy storage capacitor |
PCT/US2015/054604 WO2016057742A2 (en) | 2014-10-08 | 2015-10-08 | Ripple reduction in light emitting diode (led)-based light bulb through increased ripple on an energy storage capacitor |
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JP5576819B2 (en) * | 2011-03-23 | 2014-08-20 | パナソニック株式会社 | Lighting device and lighting apparatus |
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CN103260318B (en) * | 2013-05-30 | 2015-03-11 | 矽力杰半导体技术(杭州)有限公司 | LED drive circuit capable of adjusting light and light adjusting method thereof |
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CN107113930B (en) | 2019-05-03 |
WO2016057742A2 (en) | 2016-04-14 |
EP3205182A2 (en) | 2017-08-16 |
CN107113930A (en) | 2017-08-29 |
WO2016057742A3 (en) | 2016-07-14 |
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