Patent ID: 7642763

Claim:
A switching power supply circuit, comprising: a power source; a pulse width modulation (PWM) circuit, comprising a first output and a second output; a first switching circuit and a second switching circuit, the first switching circuit comprising a first transistor and a second transistor, the second switching circuit comprising a third transistor and a fourth transistor, the first and second switching circuits being controlled by pulse signals provided by the first and second outputs of the PWM circuit; and a first transformer and a second transformer, the first transformer comprising a first primary winding and a second primary winding, the second transformer comprising a third primary winding and a fourth primary winding; wherein when the first output supplies a high voltage, the first transistor and the third transistor are switched on, the power source, the first primary winding, and the first transistor form a first closed loop, and the power source, the second primary winding, and the third transistor form a second closed loop; and when the second output supplies a high voltage, the second and fourth transistors are switched on, the power source, the second primary winding, and the second transistor form a third closed loop, and the power source, the fourth primary winding and the fourth transistor form a fourth closed loop.