SUMMARY
The present invention is directed to a TRIAC dimmer compatible LED driver and method thereof. In one embodiment of the present disclosure, the LED driver comprises a TRIAC dimmer, a rectifier, a switching converter having at least one switch, a feedback circuit and a controller. The TRIAC dimmer receives an AC input voltage and generates an AC chopped voltage having regulated conduction phase based on the AC input voltage. The rectifier rectifies the AC chopped voltage to generate a DC chopped voltage. The switching converter converts the DC chopped voltage into a driving signal to drive the LED. The feedback circuit is coupled to the switching converter to generate a feedback signal indicative of the current flowing through the LED.
The controller comprises a dimming signal generator, a dimming signal processor and a switch control circuit. The dimming signal generator is coupled to the TRIAC dimmer and generates a dimming signal with regulated duty cycle in accordance with the AC chopped voltage. The dimming signal processor is coupled to the dimming signal generator and generates a processed dimming signal in accordance with the dimming signal. The duty cycle of the processed dimming signal is a sum of a predetermined duty cycle and the duty cycle of the dimming signal. The switch control circuit is coupled to the dimming signal processor and the feedback circuit. Based on the processed dimming signal and the feedback signal, the switch control circuit generates a control signal to control the at least one switch in the switching converter.
In one embodiment, the controller further comprises a reference signal generator coupled between the dimming signal processor and the switch control circuit. The reference signal generator generates a reference signal in accordance with the processed 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 processed dimming signal, and a second constant, wherein the first constant is larger than the second constant. The switch control circuit generates the control signal based on the reference signal and the feedback signal.
In one embodiment, the dimming signal processor is not necessary. The reference signal generator may be directly coupled to the dimming signal generator, and generate the 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.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be further understood with reference to the following detailed description and the appended drawings, wherein like elements are provided with like reference numerals.
FIG. 1 illustrates a typical TRIAC dimmer.
FIG. 2 illustrates a prior TRIAC dimmer compatible LED driver.
FIG. 3 Is a waveform of the LED driver shown in FIG. 2.
FIG. 4 is a block diagram of a LED driver in accordance with an embodiment of the present disclosure.
FIG. 5 is a dimming curve of the LED driver shown in FIG. 4.
FIG. 6 illustrates a LED driver in accordance with one embodiment of the present disclosure.
FIG. 7 illustrates a dimming signal processor in accordance with one embodiment of the present disclosure.
FIG. 8 is a waveform of the dimming signal processor shown in FIG. 7.
FIG. 9 illustrates a LED driver in accordance with one embodiment of the present disclosure.
FIG. 10 A and 10 B are the wave forms of the LED driver shown in FIG. 9.
FIG. 11 illustrates a LED driver in accordance with another embodiment of the present disclosure.
FIG. 12 is a flow chart of a method for driving LED, in accordance with an embodiment of the present disclosure.