Patent ID: 9293982
Filing Date: 2016-03-22
CPC Classification: H02M

Claim Text:
1. A switching power supply comprising: a switching power supply main body configured to switch an input voltage through a switching element at a specified frequency to apply the switched voltage to a primary winding of a transformer, and rectify and smooth an AC voltage developed across a secondary winding of the transformer to obtain a specified output voltage; a control circuit configured to conduct feedback control of a pulse width of a driving signal for switching the switching element according to the output voltage of the switching power supply main body and settle the output voltage to a specified voltage level; a frequency reducing circuit that is disposed in the control circuit and is configured to reduce a frequency of the driving signal for switching the switching element upon detection of an overload state of the switching power supply main body and limit an output current of the switching power supply; and an initial state setting circuit that is configured to set the control circuit to an overload detecting state for a predetermined period of time in a startup period of the control circuit, wherein the control circuit is further configured to compare an output signal of an oscillator, an oscillation frequency of which varies corresponding to a feedback voltage generated by detecting the DC output voltage of the switching power supply main body, with the feedback voltage, and compare the output signal of the oscillator with a control voltage for soft starting generated at the startup period of the control circuit, to generate a driving signal for switching the switching element; and the initial state setting circuit is composed of a switch circuit that is configured to pull down the control voltage for soft starting to a ground potential for a predetermined period of time in the startup period of the control circuit to inhibit generation of the driving signal, and to pull up the feedback voltage to a voltage exhibiting an overload state.