Dimmable LED Driver And Method For Controlling The Same

• US 20140125240A1
• Filed: 05/03/2012
• Published: 05/08/2014
• Est. Priority Date: 05/06/2011
• Status: Active Grant

• Current Assignee: OSRAM GmbH (Ams-Osram AG)
• Original Assignee: OSRAM GmbH (Ams-Osram AG)
• Inventors: Chen, Shaoping, Chen, Yuli, Tan, Wei, Bordin, Luca, Nie, Shijun
• Granted Patent: US 9,113,516 B2
• Time in Patent Office: Days
• US Class Current: 315/200.R
• CPC Class Codes: H05B 45/375 using buck topology

Abstract

A dimmable LED driver adapted to be operated with a dimmer that is configured to generate a predetermined conductive angle, wherein the dimmable LED driver comprises: a rectifier configured to convert an alternating current output by the dimmer to a direct current, a buck PFC block configured to adjust an output voltage of the direct current so as to obtain a stable output voltage, a second buck DC/DC block configured to realize output of a constant current after the stable output voltage is realized, a dimming block configured to, after realizing output of the constant current, accomplish a dimming function jointly with the second buck DC/DC block, and an MCU configured to control the buck PFC block, the second buck DC/DC block and the dimming block.

Claims

1. A dimmable LED driver adapted to be operated with a dimmer that is configured to generate a predetermined conductive angle, wherein the dimmable LED driver comprises:

a rectifier configured to convert an alternating current output by the dimmer to a direct current,

a buck PFC block configured to adjust an output voltage of the direct current so as to obtain a stable output voltage.

a second buck DC/DC block configured to realize output of a constant current after the stable output voltage is realized,

a dimming block configured to, after realizing output of the constant current, accomplish a dimming function jointly with the second buck DC/DC block, and

an MCU configured to control the buck PFC block, the second buck DC/DC block and the dimming block.

2. The dimmable LED driver according to claim 1, wherein the MCU adjusts a duty cycle of a PWM PFC signal that is output according to an error between a sampling value of a first sampling voltage of an output voltage of the buck PFC block and a set reference value so as to realize the output voltage that is stable and conforms to the reference value.

3. The dimmable LED driver according to claim 2, wherein the MCU, after obtaining the stable output voltage, generates a PWM dimming signal and a PWM buck signal, controls the second buck DC/DC block according to the PWM buck signal to realize output of a constant current, controls simultaneously the dimming block according to the PWM dimming signal, and realizes a dimming function jointly with the second buck DC/DC block.

4. The dimmable LED driver according to claim 1, wherein the MCU comprises an ADC, a CPU, a PWM PFC unit, a PWM buck unit, a PWM dimming unit and a comparator unit, and wherein the ADC is connected to an input end of the CPU, and output ends of the CPU are connected with input ends of the PWM PFC unit, the PWM buck unit and the PWM dimming unit, while the other input end of the PWM buck unit is connected with an output end of the comparator unit.

5. The dimmable LED driver according to claim 4, wherein the buck PFC block comprises a first MOSFET, a first MOSFET driver, a first filter inductor, a second diode, a first energy storage capacitor, a third resistor and a fourth resistor, and wherein the first MOSFET driver has an input end connected to the PWM PFC unit and an output end connected to a gate of the first MOSFET, a drain electrode of the first MOSFET is connected to a live wire output end of the rectifier through the first diode, and wherein the first diode has an anode connected to the live wire output end of the rectifier and has a cathode connected to a drain electrode of the first MOSFET, one end of the first filter inductor and the cathode of the second diode are connected to a source electrode of the first MOSFET, the other end of the first filter inductor is connected with one end of the first energy storage capacitor and one end of the third resistor to be connected with an anode of the LED, and wherein the other end of the third resistor is connected in series with the fourth resistor, and a first pin that is connected to the ADC is provided between the third resistor and the fourth resistor, and wherein the other end of the second diode is connected with the anode of the first energy storage capacitor and the other end of the fourth resistor to be grounded together.

6. The dimmable LED driver according to claim 5, wherein the MCU controls on and off of the first MOSFET through the first MOSFET driver using the PWM PFC signal, and the MCU receives a first sampling voltage fed back from the first pin.

7. The dimmable LED driver according to claim 6, wherein the MCU only adjusts the duty cycle of the PWM PFC signal at a time of each zero-crossing of an AC voltage.

8. The dimmable LED driver according to claim 4, wherein the second buck DC/DC block comprises a third diode, a second MOSFET, a second MOSFET driver, a second filter inductor, a fifth resistor and a sixth resistor, and wherein the second MOSFET driver has an input end connected to the PWM buck unit through the sixth resistor and an output end connected to a gate of the second MOSFET, a drain electrode of the second MOSFET is connected to an anode of the third diode, and a cathode of the third diode is connected to an anode of the LED, an anode of the third diode is connected to a cathode of the LED through the second filter inductor, a source electrode of the second MOSFET is connected with one end of the fifth resistor and an in-phase input end of the comparator unit, respectively, a reversed-phase input end of the comparator unit is connected with a reference voltage, and the other end of the fifth resistor is grounded.

9. The dimmable LED driver according to claim 8, wherein the MCU generates the PWM buck signal to control the second MOSFET to be turned on, a state of the comparator unit turns over when the second sampling voltage on the fifth resistor reaches the reference voltage.

10. The dimmable LED driver according to claim 9, wherein the second buck DC/DC block works in a peak current mode.

11. The dimmable LED driver according to claim 8, wherein the dimming block comprises the first and second resistors, and the fourth diode, the first and second resistors are connected in series between the live wire output end and a zero line output end of the rectifier, the other end of the second resistor is grounded jointly with the zero line output end, a second pin that is connected to the ADC is provided between the first and second resistors, and the fourth diode has a cathode connected to the PWM dimming unit and an anode connected between the sixth resistor and the second MOSFET driver, and wherein the AC voltage is rectified by the rectifier and is guided into the MCU through the second pin, and the conductive angle of the dimmer is calculated by the MCU.

12. The dimmable LED driver according to claim 11, wherein the MCU generates one channel of PWM dimming signal through the PWM dimming unit and adjusts a duty cycle of the PWM dimming signal according to the conductive angle, the PWM dimming signal is output to the second MOSFET driver through the fourth diode so as to control on and off of the second MOSFET.

13. The dimmable LED driver according to claim 12, wherein the duty cycle of the PWM dimming signal is calculated from a function D=f.

14. The dimmable LED driver according to claim 12, wherein the duty cycle of the PWM dimming signal is obtained in a manner of looking for a preset comparison table of conductive angel with duty cycle.

15. A method for controlling an LED dimmer according to, wherein the method includes the steps of:

a) initializing a system;

b) controlling a duty cycle of a PWM PFC signal of a buck PFC block through an MCU so as to realize a stable output voltage; and

c) controlling a second buck DC/DC block through the MCU so as to realize control to output of a constant current, and simultaneously, controlling a dimming block and the second buck DC/DC block through the MCU to realize dimming.

16. The method according to claim 15, wherein in step b), a first sampling voltage of the output voltage fed back is analyzed through the MCU, if a sampling value of the first sampling voltage conforms to a set reference value, carry out step c);

otherwise, adjust the duty cycle of the PWM PFC signal that is output.

17. The method according to claim 16, wherein in step c), a second sampling voltage and a reference voltage are compared through the MCU to enable a peak value current flowing through the LED to be controlled at a predetermined value.

18. The method according to claim 16, wherein in step c), a voltage, after rectified by a rectifier, is divided and sampled by the MCU to calculate a conductive angle of the dimmer and to send a PWM dimming signal to dim the LED.

19. The method according to claim 18, wherein in step c), if the conductive angle changes, the duty cycle of the PWM dimming signal is adjusted.