Abstract—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.
Index Terms—Dimming, light-emitting diode (LED),
TRIAC.