Patent ID: 7911809

Claim:
A switching power supply circuit comprising: a direct current (DC) power supply input terminal; a first transformer comprising a first primary winding; a pulse generating circuit comprising: a first switching unit and a second switching unit, each switching unit comprising a control terminal, a first conducting terminal, and a second conducting terminal, the first and second switching units connected in series between the DC power supply input terminal and ground via the conducting terminals; two voltage division resistors connected in series between the DC power supply input terminal and ground; and two capacitors, each connected in parallel with one of the two voltage division resistors; a second transformer comprising: a second primary winding connected between the control terminal and second conducting terminal of the first switching unit; a second secondary winding; and an assistant winding connected between the control terminal of the second switching unit and ground, wherein the second conducting terminal of the first switching unit is connected to ground via the second secondary winding, the first primary winding and a capacitor in series; and a startup circuit configured for controlling operation of the pulse generating circuit.