AC Power Line Controlled Light Emitting Device Dimming Circuit and Method Thereof

• US 20100308749A1
• Filed: 05/27/2010
• Published: 12/09/2010
• Est. Priority Date: 06/03/2009
• Status: Abandoned Application

• Current Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Original Assignee: Richtek Technology Corporation (MediaTek, Inc.)
• Inventors: Liu, Jing-Meng
• Application Number:
  US12/788,757
• Publication Number:
  US 20100308749A1
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The present invention discloses an AC power line controlled light emitting device dimming circuit and a method thereof. The AC power line controlled light emitting device dimming circuit includes: a light emitting device driver circuit for controlling current through a light emitting device, wherein the light emitting device is current-controlled; and a level adjustment circuit for detecting power-OFF of an AC power switch and generating a corresponding level adjustment signal which is transmitted to the light emitting device driver circuit to control the current through the light emitting device accordingly.

Claims

1. An AC power line controlled light emitting device dimming circuit comprising:

a light emitting device driver circuit for controlling current through a light emitting device, wherein the light emitting device is current-controlled; and

a level adjustment circuit for detecting power-off of an AC power switch and generating a corresponding level adjustment signal which is transmitted to the light emitting device driver circuit to control the current through the light emitting device accordingly.

2. The AC power line controlled light emitting device dimming circuit of claim 1, wherein the light emitting device is a white LED, color LED, or organic LED.

3. The AC power line controlled light emitting device dimming circuit of claim 1, wherein the level adjustment circuit includes a signal generator which generates at least one pulse in response to each power-off of the AC power switch.

4. The AC power line controlled light emitting device dimming circuit of claim 3, wherein the light emitting device driver circuit includes:

a counter counting a number of the pulses generated by the signal generator;

a conversion circuit converting the number of the pulses counted by the counter to a reference signal; and

an error amplifier comparing the reference signal with a signal relating to the current through the light emitting device, to provide an output for feedback controlling the current through the light emitting device.

5. The AC power line controlled light emitting device dimming circuit of claim 4, wherein the conversion circuit is a digital to analog converter or a mapping table circuit.

6. The AC power line controlled light emitting device dimming circuit of claim 1, wherein the level adjustment circuit includes a reference signal generator which generates a reference signal according to power-off times of the AC power switch, and the light emitting device driver circuit controls the current through the light emitting device according to the reference signal.

7. The AC power line controlled light emitting device dimming circuit of claim 6, wherein the reference signal generator includes:

a power-off detection circuit for generating at least one pulse in response to each power-off of the AC power switch;

a counter counting a number of the pulses generated by the power-off detection circuit; and

a conversion circuit converting the number of the pulses counted by the counter to a reference signal.

8. The AC power line controlled light emitting device dimming circuit of claim 7, wherein the conversion circuit is a digital to analog converter or a mapping table circuit.

9. The AC power line controlled light emitting device dimming circuit of claim 1, wherein the level adjustment circuit includes a pulse width modulation (PWM) dimming signal generator which generates a PWM dimming signal according to power-off times of the AC power switch, and wherein the light emitting device driver circuit controls the current through the light emitting device according to the PWM diming signal.

10. The AC power line controlled light emitting device dimming circuit of claim 9, wherein the PWM dimming signal generator includes:

a power-off detection circuit for generating at least one pulse in response to each power-off of the AC power switch;

a counter counting a number of the pulses generated by the power-off detection circuit;

a conversion device converting the number of the pulses counted by the counter to a first reference signal; and

a duty ratio controller for generating the PWM dimming signal, wherein the duty ratio controller receives a clock signal and adjusts a duty ratio of the PWM dimming signal according to the first reference signal.

11. The AC power line controlled light emitting device dimming circuit of claim 10, wherein the conversion device is a digital to analog converter (DAC) or a mapping table circuit.

12. The AC power line controlled light emitting device dimming circuit of claim 10, wherein the duty ratio controller includes:

a saw tooth signal generator generating a saw tooth signal; and

a comparator comparing the saw tooth signal with the first reference signal to generate the PWM diming signal.

13. The AC power line controlled light emitting device dimming circuit of claim 10, wherein the duty ratio controller includes:

a saw tooth signal generator generating a saw tooth signal, wherein a slope of the saw tooth signal is controlled by the first reference signal; and

an output circuit converting the saw tooth signal to the PWM diming signal.

14. The AC power line controlled light emitting device dimming circuit of claim 13, wherein the output circuit includes one of the following circuits:

a comparator comparing the saw tooth signal with a second reference signal;

a hysteresis buffer receiving the saw tooth signal;

or a plurality of inverters connected in series, wherein the first stage inverter of the two inverters receives the saw tooth signal.

15. The AC power line controlled light emitting device dimming circuit of claim 13, wherein the duty ratio controller further includes a low pass filter receiving an output of the output circuit to obtain an average value;

and wherein the saw tooth signal generator determines the slope of the saw tooth signal according to a difference between the first reference signal and the average value.

16. The AC power line controlled light emitting device dimming circuit of claim 1, wherein the light emitting device and the light emitting device driver circuit are coupled to different capacitors respectively.

17. The AC power line controlled light emitting device dimming circuit of claim 1, further comprising a time-out timer measuring a power-off period of the AC switch, wherein when the power-off period is longer than a predetermined period, the current through the light emitting device is reset to a default value at a next time the AC switch is turned on.

18. A method of dimming an AC power line controlled light emitting device, comprising:

providing a light emitting device, wherein the light emitting device is current-controlled;

detecting power-off of an AC power switch and generating a corresponding level adjustment signal; and

controlling a current through the light emitting device according to the level adjustment signal.

19. The diming method of claim 18, wherein the step of generating the corresponding level adjustment signal includes:

generating at least one pulse in response to each power-off of the AC power switch.

20. The diming method of claim 19, wherein the step of generating the corresponding level adjustment signal further includes:

counting a number of the pulses; and

converting the counted number to a reference signal.

21. The diming method of claim 19, wherein the step of generating the corresponding level adjustment signal further includes:

counting a number of the pulses;

converting the counted number to a reference signal; and

generating a PWM diming signal according to the reference signal.

22. The diming method of claim 18, further comprising:

resetting the current through the light emitting device to a default value when a power-off period of the AC switch is longer than a predetermined period.