Power supply voltage detection circuit of switching power supply

The utility model discloses a power supply voltage detection circuit of a switching power supply. The power supply voltage detection circuit adopts the structure that an inverting input terminal of a differential amplifier is connected with a power supply voltage sampling point through a second switch and is connected with a first output terminal through a first switch, and a non-inverting input terminal of the differential amplifier is connected with a reference voltage circuit; the input terminal of the reference voltage circuit is connected with a reference voltage calibration circuit; the input terminal of a logic control circuit, the grid electrode of the first switch and the control signal input terminal of the differential amplifier are connected with a logic control signal, and the output terminal of the logic control circuit is connected with the grid electrode of the second switch; and the logic control circuit controls the multiplexing of the differential amplifier during reference voltage calibration and voltage detection through the first switch and the second switch. By virtue of the embodiment of the utility model, the detection precision of power supply voltage can be improved.