Patent ID: 9627968
Date: 2017-04-18
CPC Classifications: H02M

Claim:
1. A step-down chopper type switching power-supply device comprising: a step-down chopper circuit, which includes a switching element connected to a DC power source and an inductor connected to the switching element; a regenerative-voltage detecting circuit, which detects regenerative voltage of the inductor in an OFF period of the switching element; a control circuit, which performs on-off control on the switching element based on an error voltage between a reference voltage and the regenerative voltage detected by the regenerative-voltage detecting circuit such that the regenerative voltage of the inductor becomes the reference voltage; an auxiliary power supply circuit, which charges a capacitor by using the regenerative voltage of the inductor in the OFF period of the switching element and supplies voltage of the capacitor as power-supply voltage to the control circuit; and an activation circuit, which supplies current to the capacitor by voltage supplied from the DC power source upon activation of the control circuit and stops supply of current to the capacitor after activation of the auxiliary power supply circuit, wherein after activation of the auxiliary power supply circuit, if the voltage supplied from the DC power source becomes equal to or less than a first threshold value, the activation circuit performs control such that current is supplied to the capacitor by the voltage supplied from the DC power source.