Abstract: A controller configured to control a power factor correction (PFC) circuit including a DC/DC converter, includes: a first external terminal receiving a full-wave rectified first voltage; a second external terminal receiving a first detection voltage generated by a current flowing through a sense resistor connected to a ground potential; an error amplifier circuit generating a second voltage by amplifying an error between a second detection voltage corresponding to the DC/DC converter's output voltage and a reference voltage; an arithmetic circuit generating a third voltage by multiplying the first and second voltages; an inverting amplifier generating a fourth voltage from the first detection voltage; a comparator comparing the third and fourth voltages; and a drive circuit driving a switching element in the PFC circuit to be turned on or off such that the switching element is turned off each time the fourth voltage becomes higher than the third voltage.

Abstract: A power factor correction circuit including a DC/DC converter includes: at least one selected from the group of first voltage dividing resistors and a first switch connected to an application end of a first voltage with a full-wave rectified waveform, and second voltage dividing resistors and a second switch connected to an application end of an output voltage of the DC/DC converter; and a controller configured to control the power factor correction circuit, wherein an on-off operation of at least one selected from the group of the first switch and the second switch is controlled based on a control signal which is input to the controller from outside to switch between a normal state and a standby state.

Abstract: A control circuit controls a power factor correction circuit including a DC-DC converter. The control circuit includes an amplifier configured to amplify a voltage commensurate with the output voltage of the DC-DC converter, a comparator configured to compare the output voltage of the amplifier with a slope voltage commensurate with the current passing through a switching element in the DC-DC converter, and a driver configured to drive the switching element based on the output voltage of the comparator. The control circuit is configured to adjust at least one of the gain of the amplifier and the gradient of the slope voltage in accordance with the load power of the DC-DC converter.