The invention discloses an active-control
valley fill circuit and a control method thereof which are mainly applied to pre-stage
power factor correction and energy accumulation of a
switching power supply. The active-control
valley fill circuit comprises an alternating-current power supply, a current
rectifier, a load, an energy storing
capacitor, a switch circuit and
control circuit, the alternating-current power supply is connected with an input end of the current
rectifier, an output end of the current
rectifier is connected with the load, the switch circuit comprises two power ends and a control end of a power channel, the energy storing
capacitor is serially connected with the two power ends of the switch circuit and is then parallelly connected with an output end of the current rectifier, and the control end of the switch circuit is connected with the
control circuit. According to the control method, by means of presetting
threshold voltage, switching between power supplying of the load and energy storing of the energy storing
capacitor is realized according to changes of relationships among alternating-current phase position
voltage,
voltage at two ends of the energy storing capacitor and the
threshold voltage. The active-control
valley fill circuit has the advantages that a circuit structure is simple, a
power factor is improved, output
voltage is not higher than alternating-current crest voltage, and the minimum value of the output voltage can be set.