Two-stage LED driver with buck PFC and improved THD
View Patent ↗A two-stage light emitting diode (LED) driver for powering an LED load at a substantially constant current, and related methods and systems. The first or front end stage of the LED driver includes a buck topology power factor correction (PFC) circuit, the buck PFC circuit and a PFC controller. The second stage of the LED driver includes a conventional isolation and regulator circuit configured to receive the DC voltage and DC current output by the buck PFC and then to provide the substantially constant current to the LED load. By multiplying the rectified input voltage sensed by the PFC controller, the input AC current drawn by the buck PFC circuit has a much improved total harmonic distortion (THD), which is achievable without the need for using an expensive PFC controller. The rectified input voltage is multiplied using a Zener diode ladder.
1. A light emitting diode (LED) driver for powering an LED load at a substantially constant current, comprising:
a buck power factor correction (PFC) circuit, having a PFC controller, the buck PFC circuit configured to (i) draw an alternating current (AC) input current having a first total harmonic distortion (THD), (ii) sense a rectified input voltage from a full-wave rectifier at the PFC controller, and (iii) output a direct current (DC) voltage and a DC current;
a passive voltage multiplier circuit (i) disposed between the full-wave rectifier and an input of the PFC controller, and (ii) configured to multiply the sensed rectified input voltage by a whole number greater than 1, the drawn AC current having a second THD different from the first THD; and
a downstream isolation and regulator circuit configured to (i) receive the DC voltage and the DC current output by the buck PFC circuit, based on the drawn AC current, and (ii) selectively switch, by a switch thereof, the DC current between different values based on a status position of the switch, to provide the substantially constant current of a desired value to the LED load.
2. The LED driver of claim 1 , wherein the passive voltage multiplier circuit comprises a Zener diode ladder that includes a plurality of Zener diode-resistor pairs and wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage to be sensed by the PFC controller, the polynomial function is defined as X″, where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder.
3. The LED driver of claim 2 , wherein the input AC current having the second THD is defined by the equation: Ip(t) =K*Vg n (t), wherein K represents a constant, Vg represents the input voltage and n is a whole number equal to or greater than 2.
4. The LED driver of claim 1 , wherein the passive voltage multiplier circuit is part of the buck PFC circuit and wherein the buck PFC circuit is configured to operate in transition mode.
5. The LED driver of claim 1 , wherein the LED driver is a two-stage LED driver, wherein the buck PFC circuit is a first stage of the two-stage LED driver and wherein the downstream isolation and regulator circuit is a second stage of the two-stage LED driver.
6. The LED driver of claim 1 , wherein the downstream isolation and regulator circuit includes a low voltage flyback circuit, wherein the amperage of the substantially constant current of the desired value to be provided to the LED load is set according to a configuration of the low voltage flyback circuit.
7. The LED driver of claim 1 , wherein the full wave rectifier is coupled to an AC power supply.
8. The LED driver of claim 7 , wherein the second, improved THD of the input AC current is lower than the first THD and wherein the second, improved THD enables the LED driver to draw less current from the AC power supply.
9. A method for powering a light emitting diode (LED) load at a substantially constant current using a two stage LED driver, comprising:
providing alternating current (AC) power from an AC power supply to a first stage of the LED driver, the first stage including a buck power factor correction (PFC) circuit and a PFC controller, the first stage of the LED driver drawing an input AC current having a first total harmonic distortion (THD);
generating a rectified input voltage from the AC power supply;
multiplying the rectified input voltage by a whole number greater than 1, by a passive voltage multiplier circuit disposed between a full-wave rectifier and input to the PFC controller, the drawn input AC current having a second THD different from the first THD;
sensing the multiplied rectified input voltage at the PFC controller;
receiving a direct current (DC) voltage and a DC current output from the buck PFC circuit, based on the drawn AC current, at a second stage of the LED driver; and
selectively switching, by a switch of a downstream isolation and regulator circuit of the second stage, the DC current between different values based on a status position of the switch, to provide the substantially constant current of a desired value to the LED load.
10. The method for powering the LED load of claim 9 , wherein multiplying the rectified input voltage is performed using a passive voltage multiplier circuit.
11. The method for powering the LED load of claim 9 , wherein multiplying the rectified input voltage is performed using a Zener diode ladder having a plurality of Zener diode-resistor pairs, each respective Zener diode-resistor pair including a Zener diode in parallel with a corresponding resistor, wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage to be sensed at the PFC controller, the polynomial function defined as X″, where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder.
12. The method for powering the LED load of claim 9 , wherein generating the rectified input voltage from the AC power supply further comprises coupling the AC power supply to a bridge rectifier.
13. The method for powering the LED load of claim 9 , further comprising operating the buck PFC circuit in transition mode.
14. The method for powering the LED load of claim 9 , wherein sensing the multiplied rectified input voltage at the PFC controller comprises providing the multiplied rectified input voltage to a voltage sensing input of the PFC controller.
15. The method for powering the LED load of claim 9 , wherein the downstream isolation and regulator circuit includes a low voltage flyback circuit, further comprising setting the amperage of the substantially constant current to the desired value to be provided to the LED load based on configuration settings of the low voltage flyback circuit.
16. A system for powering a light emitting diode (LED) load at a substantially constant current, comprising:
an alternating current (AC) power supply that provides an input AC voltage and an input AC current;
a full-wave rectifier coupled to the AC power supply that converts the input AC voltage into a rectified input voltage;
a first stage of a two stage LED driver, the first stage including a buck power factor correction (PFC) circuit operating in transition mode and a PFC controller, the buck PFC circuit configured to: (i) draw the input AC current from the AC power supply at a first total harmonic distortion (THD), (ii) receive the rectified input voltage from the full-wave rectifier at an input of the PFC controller, and (iii) output a direct current (DC) voltage and a DC current;
a passive voltage multiplier circuit positioned between the full-wave rectifier and the input of the PFC controller of the first stage, and configured to multiply the sensed rectified input voltage by a whole number greater than 1, the drawn input AC current having a second THD different from the first THD;
a second stage of the two stage LED driver, the second stage including a downstream isolation and regulator circuit configured to: (i) receive the DC voltage and the DC current output by the buck PFC circuit, based on the drawn AC current, and (ii) selectively switch, by a switch thereof, the DC current between different values based on a status position of the switch, to provide the substantially constant current of a desired value to the LED load.
17. The system for powering the LED load of claim 16 , wherein the passive voltage multiplier circuit comprises a Zener diode ladder.
18. The system for powering the LED load of claim 17 , wherein the Zener diode ladder includes a plurality of Zener diode-resistor pairs, each respective Zener diode-resistor pair including a Zener diode in parallel with a corresponding resistor, wherein the Zener diode ladder approximates a polynomial function for multiplying the rectified input voltage to be sensed at the PFC controller, the polynomial function defined as X″, where “n” is a real number corresponding to the number of Zener diode-resistor pairs in the Zener diode ladder.
19. The system for powering the LED load of claim 18 , wherein the input AC current having the second, improved THD is defined by the equation: Ip(t) =K*Vg n (t) wherein K represents a constant, Vg represents the input voltage and n represents a whole number equal to or greater than 2.
20. The system for powering the LED load of claim 16 , wherein the downstream isolation and regulator circuit includes a low voltage flyback circuit and wherein the amperage of the substantially constant current of the desired value to be provided to the LED load is set according to a configuration of the low voltage flyback circuit.
21. A light emitting diode (LED) driver for powering an LED load at a substantially constant current, comprising:
a buck power factor correction (PFC) circuit, having a PFC controller, the buck PFC circuit configured to: (i) draw an alternating current (AC) input current having a first THD, (ii) sense a rectified input voltage from a full-wave rectifier at the PFC controller, and (iii) output a direct current (DC) voltage and a DC current;
a passive voltage multiplier circuit disposed between the full-wave rectifier and an input of the PFC controller, and configured to multiply the sensed rectified input voltage by a whole number greater than 1, the drawn input AC current having a second THD different from the first THD; and
a dual low voltage flyback circuit configured to: (i) receive the DC voltage and the DC current output by the buck PFC circuit, based on the drawn AC current, and (ii) selectively switch, by a switch thereof, the DC current between different values based on a status position of the switch, and supplying the selected value to the LED load.