Patent ID: 7554825

Claim:
A switching power supply capable of reducing a low-frequency AC hum, the power supply comprising: an input AC power; an input filtering device; a first common-mode filtering circuit device; a second common-mode filtering circuit device; a filtering capacitor; a transformer & switch device having a transformer and a switch connected in series; an output filtering & voltage regulator; a pulse width modulation device; and a load, wherein: the input AC power is electrically connected to input terminals of the input filtering device; output terminals of the input filtering device are connected, in parallel, to a serial loop, which is composed of the first common-mode filtering circuit device, the second common-mode filtering circuit device and the filtering capacitor connected in series; input terminals of the filtering capacitor and the transformer & switch device are connected in parallel; output terminals of the transformer & switch device are connected to the output filtering & voltage regulator in parallel; and the load is connected to the output filtering & voltage regulator in parallel.