Direct current light emitting device control circuit with dimming function and method thereof

• US 20120062136A1
• Filed: 06/22/2011
• Published: 03/15/2012
• Est. Priority Date: 09/13/2010
• Status: Active Grant

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Tsai, Fu-Sheng, Haung, Pei-Cheng
• Granted Patent: US 8,779,690 B2
• Time in Patent Office: Days
• US Class Current: 315/224
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines

Abstract

The present invention discloses a direct current (DC) light emitting device control circuit with dimming function, and a method thereof, wherein the dimming function is provided in a feedback loop for feeding back a feedback signal from an output terminal to a power switch control circuit; the feedback signal relates to an output current supplied to the DC light emitting device. The present invention adjusts the feedback signal according to the desired brightness of the DC light emitting device. The present invention controls a power switch according to the adjusted feedback signal, such that the output current supplied to the DC light emitting device is adjusted, and accordingly the brightness of the DC light emitting device is adjusted below the full brightness.

Claims

1. A direct current light emitting device control circuit with a dimming function, comprising:

at least one power switch;

a switch control circuit controlling the power switch to convert an input voltage to an output current which is supplied to at least one direct current light emitting device;

a feedback circuit generating a feedback signal according to a signal related to the output current; and

a dimming circuit coupled to the feedback circuit, the dimming circuit adjusting the feedback signal to generate an adjusted feedback signal, wherein the switch control circuit receives the adjusted feedback signal and controls the power switch according to the adjusted feedback signal whereby the output current supplied to the direct current light emitting device is adjusted to achieve the dimming function.

2. The direct current light emitting device control circuit with a dimming function of claim 1, wherein the dimming circuit includes a variable resister connected to the feedback circuit in series or in parallel.

3. The direct current light emitting device control circuit with a dimming function of claim 1, wherein the dimming circuit includes an adjustable gain amplifier having an input coupled to the feedback signal and an output coupled to the switch control circuit.

4. The direct current light emitting device control circuit with a dimming function of claim 1, wherein the dimming circuit includes a parallel circuit coupled to an output terminal of the feedback circuit, the parallel circuit includes a switch, and the feedback signal is adjusted by turning on or off the switch.

5. The direct current light emitting device control circuit with a dimming function of claim 4, wherein the parallel circuit includes at least two parallel paths and at least one of the parallel paths includes the switch to activate or inactivate the path.

6. The direct current light emitting device control circuit with a dimming function of claim 1, wherein the power switch is a power switch of a primary side circuit in an AC to DC converter and the feedback circuit includes a phototransistor.

7. The direct current light emitting device control circuit with a dimming function of claim 1, wherein the power switch is a power switch of a DC to DC converter.

8. A control method for dimming a direct current light emitting device, comprising:

controlling at least one power switch to convert an input voltage to an output current which is supplied to at least one direct current light emitting device;

generating a feedback signal according to a signal related to the output current;

adjusting the feedback signal to generate an adjusted feedback signal according to a brightness of the direct current light emitting device which is below full brightness; and

controlling the power switch according to the adjusted feedback signal such that the output current supplied to the direct current light emitting device is adjusted, whereby the brightness of the direct current light emitting device is controllable below full brightness to achieve the dimming function.

9. The control method for dimming a direct current light emitting device of claim 8, wherein the power switch also converts the input voltage to an output voltage and the step of controlling the power switch according to the adjusted feedback signal includes:

controlling the power switch according to the adjusted feedback signal to change a level of the output voltage;

detecting a change in the level of the output voltage; and

adjusting the output current supplied to the direct current light emitting device according to the change in the level of the output voltage to achieve the dimming function.

10. The control method for dimming a direct current light emitting device of claim 9, wherein the level of the output voltage periodically varies between a high level and a low level and a duty ratio of each period determines the output current supplied to the direct current light emitting device.

11. The control method for dimming a direct current light emitting device of claim 9, wherein the level of the output voltage is at a normal level in a steady status, but the output voltage is raised to a level higher than the normal level when the feedback signal is adjusted, and a difference between the higher level and the normal level determines the output current supplied to the direct current light emitting device.

12. The control method for dimming a direct current light emitting device of claim 9, wherein the level of the output voltage is at a medium level in a steady status, but the output voltage is raised to a high level to generate a positive pulse or the output voltage is lowered to a low level to generate a negative pulse when the feedback signal is adjusted, and the step of adjusting the output current supplied to the direct current light emitting device according to the change in the level of the output voltage includes:

upward adjusting the output current supplied to the direct current light emitting device one level according to the positive pulse or downward adjusting the output current supplied to the direct current light emitting device one level according to the negative pulse.

13. The control method for dimming a direct current light emitting device of claim 9, wherein the level of the output voltage is at a normal level in a steady status, but the output voltage is raised to a level higher than the normal level when the feedback signal is adjusted, and a duration of the higher level determines the output current supplied to the direct current light emitting device.

14. The control method for dimming a direct current light emitting device of claim 9, wherein the step of generating a feedback signal includes:

comparing the signal related to the output current with a reference signal; and

wherein the step of adjusting the output current supplied to the direct current light emitting device according to the change in the level of the output voltage includes;

adjusting the reference signal according to the change in the level of the output voltage.