Dimming-Feedback Control Method for TRIAC Dimmable LED Drivers

This paper presents a small-signal ac modeling of a feedback system for a flyback light-emitting diode (LED) driver. From this analysis, a dimming-feedback control method, which has a constant loop gain at dc, is proposed for dimmable LED drivers. Since the proposed method controls the steady-state error of the feedback system, an additional phase angle detection circuit and a LED current adjusting circuit are not required to control the output LED current according to the phase angle of the input voltage in a TRIAC-dimmable LED driver. Therefore, the proposed control method provides a simple structure, small size, and low bill of materials. A prototype of a flyback LED driver with the proposed dimming-feedback control method is implemented and experimented on to verify the validity of the analysis and the proposed control method. The prototype shows that the proposed control method varies the output LED current according to the phase angle of the TRIAC dimmer with no additional circuits. Thus, the proposed control method has high compatibility with TRIAC dimmers and can be applied to any dimmable LED driver with a nondimmable control integrated circuit.