Patent ID: 8725023

Claim:
A power supply system comprising: a switching power supply configured to output a first output voltage in normal output mode and a second output voltage lower than the first output voltage in low output mode; and a control unit configured to switch the mode of the switching power supply, the switching power supply comprising: a transformer configured to induce a voltage in a secondary side by oscillation of a primary side; a semiconductor switch connected to a primary coil of the transformer; a rectifier/smoothing circuit configured to rectify and smooth the voltage induced in the secondary side of the transformer; an overcurrent detection circuit configured to detect an overcurrent in the switching power supply and provided on the secondary side of the transformer, the overcurrent detection circuit comprising: a current detecting resistor configured to obtain a voltage proportional to an output current of the switching power supply; a reference voltage generation circuit configured to generate a first reference voltage in a condition that the output voltage of the switching power supply is the first output voltage and a second reference voltage lower than the first reference voltage in a condition that the output voltage of the switching power supply is the second output voltage; and a comparison circuit configured to detect the overcurrent by comparing the voltage across the current detecting resistor with the first reference voltage or the second reference voltage; and a switch control circuit configured to control the semiconductor switch in a condition that the overcurrent is detected and thereby reducing the overcurrent.