ADAPTIVE FREQUENCY COMPENSATION FOR PFC POWER CONVERTER OPERATING IN CCM AND DCM
A control circuit of a power factor correction (PFC) converter is provided. The control circuit includes a pulse width modulation (PWM) circuit, an amplifier, a detection circuit., and a capacitor. The PWM circuit generates a switching signal in response to a loop signal. The amplifier is coupled to generate the loop signal in response to a switching current. The detection circuit generates a mode signal coupled to change output impedance of the amplifier. The capacitor is coupled to the amplifier for loop frequency compensation. The switching signal is coupled to switch an inductor of the PFC power converter and generate the switching current.
1 . A control circuit of a power factor correction (PFC) converter comprising:
a pulse width modulation (PWM) circuit generating a switching signal in response to a loop signal;
an amplifier coupled to receive a switching current for generating the loop signal;
a detection circuit generating a mode signal coupled to change output impedance of the amplifier; and
a capacitor coupled to the amplifier for loop frequency compensation;
wherein the switching signal is coupled to switch an inductor of the PFC power converter and generate the switching current.
2 . The circuit as claimed in claim 1 , wherein the mode signal indicates a CCM (continuous current mode) or DCM (discontinuous current mode) operation.
3 . The circuit as claimed in claim 1 , wherein the mode signal is generated in response to an input voltage of the PFC power converter, an output voltage of the PFC power converter, and the switching signal.
4 . The circuit as claimed in claim 1 , wherein the amplifier is a transconductance amplifier.
5 . The circuit as claimed in claim 1 , wherein the mode signal is coupled to change a bias current of the amplifier.
6 . The circuit as claimed in claim 1 , wherein the loop signal is a current loop signal generated by comparing the switching current with a command signal.
7 . The circuit as claimed in claim 6 , wherein the command signal is generated
8 . A method for controlling a power factor correction (PFC) converter comprising:
generating a switching signal in response to a loop signal;
generating the loop signal in accordance with a switching current;
generating a mode signal coupled to change the impedance of the loop signal;
compensating the loop signal with a capacitor;
wherein the switching signal is coupled to switch an inductor of the PFC power converter and generate the switching current.
9 . The method as claimed in claim 8 , wherein the mode signal indicates a CCM (continuous current mode) or DCM (discontinuous current mode) operation.
10 . The method as claimed in claim 8 , wherein the mode signal is generated in response to an input voltage of the PFC power converter, an output voltage of the PFC power converter, and the switching signal.
11 . The method as claimed in claim 8 , wherein the loop signal is generated by a transconductance amplifier.
12 . The method as claimed in claim 8 , wherein the mode signal is coupled to change a bias current of the transconductance amplifier.
13 . The method as claimed in claim 8 , wherein the loop signal is a current loop signal generated by comparing the switching current with a command signal.
14 . The method as claimed in claim 13 , wherein the command signal is generated in response to an input voltage of the PFC power converter.
15 . The method as claimed in claim 8 , wherein the impedance associated with the loop signal and capacitance of the capacitor develop a low-pass filter for the loop signal.