LED driving device

1. A light-emitting diode (LED) driving device comprising:

a rectifier configured to convert alternating current (AC) power to direct current (DC) power;

a convertor including:

a transformer including a primary-side winding connected to the rectifier; and

a main switch connected to the primary-side winding of the transformer;

a controller configured to output a control signal to the main switch in response to a feedback signal; and

an output modifier configured to modify the feedback signal;

wherein:

the output modifier includes a resistance circuit having variable resistance and is connected to the main switch in series; and

the resistance circuit includes a plurality of resistors connected to each other in parallel, and at least one switching element configured to connect or disconnect the resistors to and from each other.

2. The LED driving device of claim 1 , wherein the controller is further configured to adjust at least one of an operating frequency and a duty cycle ratio of the control signal.

3. The LED driving device of claim 1 , further comprising an output circuit connected to a secondary-side winding of the transformer and configured to supply driving power to at least one light-emitting diode (LED).

4. The LED driving device of claim 1 , wherein the controller is configured to increase a driving power by raising at least one of an operating frequency and a duty cycle ratio of the control signal, and to reduce the driving power by lowering at least one of the operating frequency and the duty cycle ratio of the control signal.

5. The LED driving device of claim 1 , wherein the output modifier further includes an inductance modifier connected to the primary-side winding of the transformer and configured to selectively modify an inductance of the primary-side winding of the transformer.

6. The LED driving device of claim 5 , wherein the inductance modifier includes a switching element connected in parallel across at least a portion of the primary-side winding of the transformer.

7. The LED driving device of claim 5 , further comprising a second output modifier including a time constant control circuit having a variable resistance and configured to adjust a time constant of the main switch.

8. The LED driving device of claim 1 , further comprising a second output modifier including a time constant control circuit having a variable resistance and configured to adjust a time constant of the main switch.

9. The LED driving device of claim 8 , wherein the time constant control circuit is connected to at least one capacitor included in the controller and is configured to adjust a time in which the at least one capacitor is charged or discharged.

10. A light-emitting diode (LED) driving device comprising:

a rectifier configured to convert alternating current (AC) power to direct current (DC) power;

a convertor including:

a transformer including a primary-side winding connected to the rectifier;

a main switch connected to the primary-side winding of the transformer; and

an inductance modifier connected to a primary-side winding of the transformer and configured to selectively modify a primary-side inductance of the transformer; and

a controller configured to output a control signal to the main switch in response to a feedback signal from the convertor;

wherein the inductance modifier includes a switching element connected in parallel across at least a portion of the primary-side winding of the transformer.

11. The LED driving device of claim 10 , further comprising an output circuit connected to a secondary side of the transformer and configured to supply a driving power to at least one LED.

12. The LED driving device of claim 10 , further comprising an output modifier including a time constant control circuit having a variable resistance and configured to adjust a time constant of the main switch.

13. The LED driving device of claim 12 , wherein the time constant control circuit is connected to at least one capacitor included in the controller and is configured to adjust a time in which the at least one capacitor is charged or discharged.

14. A light-emitting diode (LED) driving device comprising:

a rectifier configured to convert alternating current (AC) power to direct current (DC) power;

a convertor including:

a transformer including a primary-side winding connected to the rectifier; and

a main switch connected to the primary-side winding of the transformer;

a controller configured to output a control signal to the main switch in response to a feedback signal from the convertor; and

an output modifier configured to modify a time constant of the main switch

wherein:

the output modifier includes a time constant control circuit having a variable resistance; and

the time constant control circuit is connected to at least one capacitor included in the controller and is configured to adjust a time in which the at least one capacitor is charged or discharged.

15. The LED driving device of claim 14 , further comprising an auxiliary winding connected to a power supply input of the controller, wherein the controller is configured to detect a voltage of the auxiliary winding.