System and method for a constant current source LED driver

• US 20100164404A1
• Filed: 04/10/2009
• Published: 07/01/2010
• Est. Priority Date: 12/31/2008
• Status: Active Grant

• Current Assignee: STMicroelectronics International N.V. (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Lo Giudice, John S., Stamm, Thomas A., Shao, Jianwen
• Granted Patent: US 8,373,356 B2
• Time in Patent Office: Days
• US Class Current: 315/297
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A system and method for providing a constant current source driver for a light emitting diode string. The converter includes a current sensor that derives feedback signal corresponding to a peak current through the light emitting diode string. The feedback signal is used by a controller to vary a duty cycle of the controller to regulate the average current. The controller is operable to regulate the average current as the number of light emitting diodes is increased and/or decreased.

Claims

1. A converter comprising:

a current sensor configured to derive a feedback signal corresponding to a peak current through a light emitting diode string;

a switch coupled on a first end to the current sensor; and

a controller coupled on a first port to a second end of the switch and on a second port to the current sensor, wherein the controller is configured to use the feedback signal corresponding to the peak current to regulate the average current.

2. The converter as set forth in claim 1, wherein the current sensor comprises a voltage divider.

3. The converter as set forth in claim 2, wherein the current sensor comprises a transformer.

4. The converter as set forth in claim 1, wherein the feedback signal is at least one of a source voltage and a voltage across the light emitting diode string.

5. The converter as set forth in claim 1, the current sensor comprising:

a first resistor coupled on a first end to a cathode of a last light emitting diode in the light emitting diode string and on a second end to the second port of the controller, wherein an anode of a first light emitting diode in the light emitting diode string is coupled to ground; and

a second resistor coupled on a first end via a third resistor to the anode of the first light emitting diode.

6. The converter as set forth in claim 1, wherein the controller and the switch are included in a control module.

7. The converter as set forth in claim 1, wherein the controller regulates the average current by varying one of a duty cycle and a switching frequency.

8. A light emitting diode system comprising:

a light emitting diode string; and

power converter, the power converter comprising;

a current sensor configured to derive a feedback signal corresponding to a peak current through the light emitting diode string;

a switch coupled on a first end to the current sensor; and

a controller coupled on a first port to a second end of the switch and on a second port to the current sensor, wherein the controller is configured to use the feedback signal corresponding to the peak current to regulate the average current.

9. The light emitting diode system as set forth in claim 8, wherein the current sensor comprises a voltage divider.

10. The light emitting diode system as set forth in claim 9, wherein the current sensor comprises a transformer.

11. The light emitting diode system as set forth in claim 8, wherein the feedback signal is at least one of a source voltage and a voltage across the light emitting diode string.

12. The light emitting diode system as set forth in claim 8, the current sensor comprising:

a first resistor coupled on a first end to a cathode of a last light emitting diode in the light emitting diode string and on a second end to the second port of the controller, wherein an anode of a first light emitting diode in the light emitting diode string is coupled to ground; and

a second resistor coupled on a first end via a third resistor to the anode of the first light emitting diode.

13. The light emitting diode system as set forth in claim 8, wherein the controller and the switch are included in a control module.

14. The light emitting diode system as set forth in claim 8, wherein the controller regulates the average current by varying one of a duty cycle and a switching frequency.

15. For use in a light emitting diode system, a method of providing a constant current source, the method comprising:

sensing a peak current through a plurality of light emitting diodes;

deriving a feedback signal corresponding to the peak current;

regulating the average current based on the feedback signal, wherein regulating further comprises varying a duty cycle of a controller.

16. The method as set forth in claim 15, wherein the step of sensing is performed by a current sensor, the current sensor comprising a voltage divider.

17. The method as set forth in claim 16, wherein the current sensor further comprises a transformer.

18. The method as set forth in claim 15, wherein the feedback signal is at least one of a source voltage and a voltage across the plurality of light emitting diodes.

19. The method as set forth in claim 15, the step of sensing is performed by a current sensor, the current sensor comprising:

a first resistor coupled on a first end to a cathode of a last light emitting diode in the plurality light emitting diodes and on a second end to the second port of the controller, wherein an anode of a first light emitting diode in the plurality of light emitting diodes is coupled to ground; and

a second resistor coupled on a first end via a third resistor to the anode of the first light emitting diode.

20. The method as set forth in claim 15, wherein the step of regulating the average current is performed by a control module, the control module comprising a controller and a switch.