Patent ID: 9680369
Date: 2017-06-13
CPC Classifications: H02M,Y02B,Y02P

Claim:
1. A power factor correction circuit of a flyback power converter, the flyback power converter comprising a primary side coil, a secondary side coil, an inductive coil, and a power switch, wherein a first terminal of the primary side coil is coupled with an input voltage signal, a first terminal of the secondary side coil is coupled with an output voltage signal, the inductive coil is configured to operably sense the primary side coil to generate an inductive signal, and the power switch is coupled between a second terminal of the primary side coil and a fixed-voltage terminal, the PFC circuit comprising: a zero current detection circuit configured to operably detect the inductive signal when coupling with the inductive coil to generate a detection signal; an error detection circuit configured to operably generate an error signal corresponding to the output voltage signal or an output current signal of the flyback power converter according to a reference signal; a ramp signal generating circuit configured to operably generate a ramp signal; a comparison circuit coupled with the error detection circuit and the ramp signal generating circuit, and configured to operably compare the ramp signal with the error signal to generate a comparison signal; and a trigger circuit coupled with the zero current detection circuit, the ramp signal generating circuit, and the comparison circuit, and configured to operably generate a control signal for controlling the power switch according to the detection signal and the comparison signal, and configured to operably control the ramp signal generating circuit to adjust a slope of the ramp signal; wherein the ramp signal generating circuit comprises: a first switch coupled between a setting signal input terminal and a node, wherein the setting signal input terminal is utilized for receiving a setting voltage; a second switch coupled between the node and a fixed-voltage terminal; a control circuit coupled with a control terminal of the first switch and a control terminal of the second switch, and configured to operably switch the first switch and the second switch alternatively under control of the trigger circuit, so as to render the node to provide an adjusted voltage less than the setting voltage; a low-pass filter coupled with the node and configured to operably perform a low-pass filtering operation on the adjusted voltage to generate a filtered signal; a transconductance amplifier coupled with the low-pass filter and configured to operably convert the filtered signal into the ramp signal; a capacitor coupled with an output terminal of the transconductance amplifier; and a third switch coupled between the output terminal of the transconductance amplifier and a fixed-voltage terminal, wherein a control terminal of the third switch is coupled with the trigger circuit.