Power supply apparatus and driving method thereof

1. A power supply apparatus comprising:

a dimmer configured to control externally input power;

a converter including a switch, and configured to convert an output of the dimmer according to a duty of the switch and to supply a first current to a load;

a dimming feedback unit configured to receive a first voltage corresponding to the first current, and having a DC finite gain;

wherein the dimming feedback unit comprises:

an amplifier having the first voltage input to a first input terminal thereof and a predetermined reference voltage input to a second input terminal thereof, wherein the reference voltage does not fluctuate based on the output of the dimmer; and

a controller configured to control the duty of the switch according to an output of the dimming feedback unit.

2. The power supply apparatus of claim 1 , wherein when an angle of an output waveform of the dimmer is decreased, the first current is decreased, and when the angle of the output waveform of the dimmer is increased, the first current is increased.

3. The power supply apparatus of claim 1 , wherein the dimming feedback unit comprises:

a first resistor coupled between the first input terminal and an output terminal of the amplifier.

4. The power supply apparatus of claim 3 , wherein the dimming feedback unit further comprises a first capacitor coupled between the first input terminal and the output terminal of the amplifier.

5. The power supply apparatus of claim 4 , wherein the dimming feedback unit further comprises a second resistor and a second capacitor coupled in series between the first input terminal and the output terminal of the amplifier.

6. The power supply apparatus of claim 5 , wherein the amplifier is a differential amplifier, and the first voltage is input to the first input terminal through a third resistor.

7. The power supply apparatus of claim 3 , wherein the desired reference voltage is a fixed value.

8. The power supply apparatus of claim 1 , wherein the dimming feedback unit comprises:

an amplifier having the first voltage input to a first input terminal thereof and a desired reference voltage input to a second input terminal; and

a first resistor coupled between an output terminal of the amplifier and a ground.

9. The power supply apparatus of claim 8 , wherein the dimming feedback unit further comprises a first capacitor coupled between the output terminal of the amplifier and the ground.

10. The power supply apparatus of claim 9 , wherein the dimming feedback unit further comprises a second capacitor and a second resistor coupled in series between the output terminal of the amplifier and the ground.

11. The power supply apparatus of claim 8 , wherein the amplifier is a mutual conductance amplifier.

12. The power supply apparatus of claim 1 , further comprising a rectification unit configured to rectify an output of the dimmer and to supply the rectified value to the converter.

13. The power supply apparatus of claim 1 , wherein the load includes light-emitting diodes (LEDs).

14. The power supply apparatus of claim 1 , wherein the first voltage is generated using the first current and the first voltage is supplied to the dimming feedback unit.

15. The power supply apparatus of claim 1 , wherein the converter further comprises a transformer, and the power supply apparatus further comprises an output current estimation unit configured to generate the first voltage corresponding to the first current using primary side information of the transformer and to provide the first voltage to the dimming feedback unit.

16. A method for driving a power supply apparatus including a switch, converting externally input power through a duty of the switch and supplying a first current to a load, the method comprising:

controlling the input power;

rectifying the controlled power;

converting the rectified power through the duty of the switch and providing the first current to the load;

comparing the first voltage corresponding to the first current with a predetermined reference voltage and generating a second voltage, wherein the reference voltage does not fluctuate based on the controlled power; and

controlling the duty of the switch corresponding to the second voltage,

wherein a transfer function, which is a ratio of the first voltage and the second voltage, has a finite DC gain.

17. The method for driving the power supply apparatus of claim 16 , wherein the first current is proportional to the controlled power.

18. The method for driving the power supply apparatus of claim 16 , wherein the reference voltage has a fixed value.

19. The method for driving the power supply apparatus of claim 16 , wherein the comparing comprises:

comparing the first voltage to the reference voltage using an amplifier and generating the second voltage with the amplifier, wherein

a first input terminal of the amplifier is coupled to the first voltage and a second input terminal of the amplifier is coupled to the reference voltage,

a first resistor is coupled between the first input terminal and an output terminal of the amplifier, and

the second voltage is output to the output terminal of the amplifier.

20. The method for driving the power supply apparatus of claim 19 , wherein a first capacitor is coupled between the first input terminal and the output terminal of the amplifier.

21. The method for driving the power supply apparatus of claim 20 , wherein a second resistor and a second capacitor are coupled in series between the first input terminal and the output terminal of the amplifier.

22. The method for driving the power supply apparatus of claim 19 , wherein the amplifier is a differential amplifier.

23. The method for driving the power supply apparatus of claim 16 , wherein the load includes light-emitting diodes (LEDs).