Patent ID: 8853957

Claim:
A constant current LED driver comprising: a rectification bridge; a power factor correction (“PFC”) main circuit; an isolated DC/DC converter; a PFC controller; and a PFC bus control circuit; wherein the rectification bridge is configured to rectify an AC input voltage (Vac) and output a first DC voltage (Vdc) to the PFC main circuit; wherein the PFC main circuit is configured to receive the first DC voltage (Vdc) from the rectification bridge and a feedback voltage from the PFC controller, and output a second DC voltage (Vbus) to the isolated DC/DC converter; wherein the isolated DC/DC converter is configured to receive the second DC voltage (Vbus) from the PFC main circuit, and output a third DC voltage (Vo) toan LED load and supply a constant current to the LED load; wherein the PFC controller is configured to receive a control signal from the PFC bus control circuit, and send the feedback signal to the PFC main circuit; wherein the PFC bus control circuit is configured to sample the signal from the third DC voltage (Vo) of the isolated DC/DC converter or an equivalent voltage of the third DC voltage (Vo), and output the control signal to the PFC controller; wherein the second DC voltage (Vbus) changes with the third DC voltage (Vo); and wherein the PFC bus control circuit further comprises an output voltage sampling circuit and a PFC output voltage modulation circuit, wherein an input voltage signal of the output voltage sampling circuit comes from an auxiliary winding in a main transformer (T 1 ) of the isolated DC/DC converter, and it is configured to maintain a peak signal with a diode (D 4 ) and a capacitor (C 4 ), and wherein the output voltage sampling circuit is further configured to convert the peak signal to a signal that is proportional to the third DC voltage (Vo), and to feed the signal to the PFC output voltage modulation circuit, and wherein the output terminal of the PFC output voltage modulation circuit is configured to connect with the input terminal of the PFC controller.