Switching control circuit and power factor correction circuit

A power factor correction circuit, comprising:

• an inductor configured to receive a rectified voltage corresponding to an alternating current (AC) voltage;
• a transistor configured to control an inductor current flowing through the inductor;
• and
• a switching control circuit configured to control switching of the transistor, wherein
• the switching control circuit includes
• a driving signal output circuit configured to,
• when a peak value of the inductor current in a half cycle of the AC voltage is smaller than a first predetermined value, output a driving signal to operate the power factor correction circuit in a critical mode, and
• when the peak value in the half cycle is greater than the first predetermined value, output the driving signal to operate the power factor correction circuit in a continuous mode, and
• a driver circuit configured to drive the transistor, in response to the driving signal,
• wherein
• the driving signal output circuit includes
• a first command value output circuit configured to output a first command value to cause the transistor to be on for a first time period, based on a feedback voltage corresponding to the output voltage and a reference voltage,
• a second command value output circuit configured to,
• when the first time period is shorter than a first predetermined time period, output a second command value to cause the transistor to be on for the first time period, and
• when the first time period is longer than the first predetermined time period, output the second command value to cause the transistor to be on for a second time period equal to or shorter than the first predetermined time period,
• an ON signal output circuit configured to,
• when the first time period is shorter than the first predetermined time period, output an ON signal to turn on the transistor, in response to the inductor current reaching a first current corresponding to the critical mode, and
• when the first time period is longer than the first predetermined time period, output the ON signal, in response to the inductor current reaching a second current corresponding to the continuous mode, and
• a signal output circuit configured to output the driving signal, based on the second command value and the ON signal, wherein
• the first predetermined time period is a time period during which the transistor is on when the peak value of the inductor current in the half cycle is the first predetermined value.

A switching control circuit for a power factor correction circuit configured to generate an output voltage at a target level from an alternating current (AC) voltage inputted thereto, the power factor correction circuit including

• an inductor configured to receive a rectified voltage corresponding to the AC voltage, and
• a transistor configured to control an inductor current flowing through the inductor, the switching control circuit being configured to control switching of the transistor, the switching control circuit comprising:
• a driving signal output circuit configured to,
• when a peak value of the inductor current in a half cycle of the AC voltage is smaller than a first predetermined value, and an average value of the inductor current in the half cycle is a first value, output a driving signal to operate the power factor correction circuit in a critical mode,
• when the peak value in the half cycle is smaller than the first predetermined value, and the average value of the inductor current in the half cycle is a second value larger than the first value, output the driving signal to operate the power factor correction circuit in the critical mode, and
• when the peak value in the half cycle is greater than the first predetermined value, and the average value of the inductor current in the half cycle is a third value larger than the second value, output the driving signal to operate the power factor correction circuit in a continuous mode;
• and
• a driver circuit configured to drive the transistor, in response to the driving signal.