Method and apparatus to control a power factor correction circuit

A power factor correction (PFC) controller for use in a PFC converter, the PFC controller comprising:

• an on time control circuit configured to generate a switch power off signal to terminate an on time of a power switch of the PFC converter, the on time control circuit including:
• an amplifier coupled to generate an error signal that is representative of a difference between a feedback signal and a reference value, wherein the feedback signal is representative of an output of the PFC converter;
• an integrator coupled to integrate a current sense signal that is representative of a current through the power switch to generate an integrator output signal, wherein a gain of the integrator is varied in response to a voltage sense signal that is representative of a value of an input voltage of the PFC converter;
• and
• a comparator coupled to the integrator and to the amplifier to generate the switch power off signal in response to comparing the integrator output signal with the error signal;
• and
• on/off logic coupled to the on time control circuit to generate a switching signal to control switching of the power switch, wherein the on/off logic terminates the on time of the switch in response to the switch power off signal.

A power factor correction (PFC) converter, comprising:

• an energy transfer element coupled to an input of the PFC converter;
• a power switch coupled to the energy transfer element;
• and
• a PFC controller coupled to the power switch, the PFC controller comprising:
• an on time control circuit configured to generate a switch power off signal, the on time control circuit including:
• an amplifier coupled to generate an error signal that is representative of a difference between a feedback signal and a reference value, wherein the feedback signal is representative of an output of the PFC converter;
• an integrator coupled to integrate a current sense signal that is representative of a current through the power switch to generate an integrator output signal, wherein a gain of the integrator is varied in response to a voltage sense signal that is representative of a value of an input voltage of the PFC converter;
• and
• a comparator coupled to the integrator and to the amplifier to generate the switch power off signal in response to comparing the integrator output signal with the error signal;
• and
• on/off logic coupled to the on time control circuit to generate a switching signal to control switching of the power switch, wherein the on/off logic terminates the on time of the switch in response to the switch power off signal.