A dimming-feedback control method, which has a constant loop gain at dc, is proposed for triac dimming LED power supply. Since the proposed way 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 ac phase cut dimming LED driver.

A prototype of a flyback LED driver with the proposed dimming-feedback control way is implemented and experimented on to verify the validity of the analysis . It shows that the proposed control method varies the output current based on the phase angle of the TRIAC dimmer without additional circuits. Thus, the proposed control method has high compatibility with TRIAC dimmers.