Patent ID: 8054600
Filing Date: 2011-11-08
Classification: H02H

Abstract:
1. A switching power supply device, comprising: an input rectifying/smoothing circuit that rectifies and smoothes an AC input voltage and outputs a DC input voltage; a switching element connected to an output end of the input rectifying/smoothing circuit through a primary winding of a transformer; an output rectifying/smoothing circuit that rectifies and smoothes a voltage induced in a secondary winding of the transformer and outputs a DC output voltage; and a control circuit that controls ON and OFF of the switching element, wherein the control circuit includes an overvoltage protection circuit that directly detects a voltage that is proportional to an amplitude of the AC input voltage and detects a voltage corresponding to the DC output voltage, outputs an overvoltage operation prohibition signal for prohibiting ON and OFF operations of the switching element when the voltage corresponding to the DC output voltage rises to a first threshold value or more, and releases the overvoltage operation prohibition signal when a low-input protection circuit directly detects that the voltage proportional to the amplitude of the AC input voltage falls below a second threshold value by discontinuing the AC input voltage by discontinuing the AC input voltage.