Switching power supply circuit including forward converter

A switching power supply circuit comprising:

• forward converter means coupled to a DC (direct current) power supply means having positive and negative terminals;
• said forward converter means including:
• (1) switching transformer means having first and second primary windings and a secondary winding magnetically coupled to said first and second primary windings, said first and second primary windings being coupled in series with said positive and negative terminals of the DC power supply means;
• (2) first switching means connected between said positive terminal and one end of the first primary winding;
• (3) second switching means connected between the other end of the first primary winding and one end of the second primary winding;
• (4) third switching means connected between the other end of the second primary winding and the negative terminal, said first, second and third switching means being series-coupled via said series-connected first and second primary windings to the DC power supply means, and arranged to be substantially simultaneously turned on/off;
• and
• (5) means coupled between each end of said first and second primary windings and the DC power supply means, for returning to the DC power supply means a counterelectromotive force induced in said first and second primary windings, while said first to third switching means are substantially simultaneously turned off, wherein electromagnetic fluxes induced in the switching transformer means are reset during a turning-off period of said first to third switching means.