High power factor primary regulated offline LED driver

摘要

A fly-back type switched current regulator includes a primary transformer winding coupled to receive a rectified DC signal derived from an AC signal. The drain of a power transistor is coupled to the primary winding, with the source of the power transistor coupled to an input of a comparison circuit and a primary transformer winding sense resistor. A control terminal of the power transistor is coupled to an output of the comparison circuit. A capacitor stores a variable reference signal for application at a first capacitor terminal to another input of the differential circuit. The variable reference signal is compared to a winding current signal generated by the sense resistor by the comparison circuit. An injection circuit applies an AC signal derived from the rectified DC signal to a second terminal of the capacitor so as to modulate the stored variable reference signal. The regulator is coupled to drive LEDs.