Triac dimmer compatible led driver and method thereof

A controller used in a LED driver, wherein the LED driver comprises a TRIAC dimmer configured to receive an AC input voltage and generate an AC chopped voltage having regulated conduction phase based on the AC input voltage, a rectifier configured to generate a DC chopped voltage in accordance with the AC chopped voltage, and a switching converter having at least one switch, wherein the switching converter converts the DC chopped voltage into a driving signal to drive LED, the controller comprises:

• a dimming signal generator coupled to the TRIAC dimmer, wherein the dimming signal generator generates a dimming signal with regulated duty cycle in accordance with the AC chopped voltage;
• a reference signal generator coupled to the dimming signal generator, wherein the reference signal generator generates a reference signal in accordance with the dimming signal, the average value of the reference signal is the difference between the product of a first constant and the duty cycle of the dimming signal, and a second constant, wherein the first constant is larger than the second constant;
• and
• a switch control circuit coupled to the reference signal generator, wherein based on the reference signal and a feedback signal indicative of the current flowing through LED, the switch control circuit generates a control signal to control the at least one switch.

A method for driving a LED, comprising:

• receiving an AC chopped voltage with regulated conduction phase from a TRIAC dimmer;
• rectifying the AC chopped voltage to generate a DC chopped voltage;
• converting the DC chopped voltage into a driving signal to drive the LED through a switching converter having at least one switch;
• generating a dimming signal with regulated duty cycle in accordance with the AC chopped voltage;
• generating a processed dimming signal in accordance with the dimming signal, wherein the duty cycle of the processed dimming signal is a sum of a predetermined duty cycle and the duty cycle of the dimming signal;
• generating a feedback signal indicative of the current flowing through LED;
• and
• generating a control signal based on the processed dimming signal and the feedback signal to control the at least one switch.