Patent ID: 8264861

Claim:
A transformer-coupled push pull power conversion circuit comprises a first and second main switching FETs each comprising a drain terminal; and a circuit bridging the drains of the first and second main switching FETs wherein upon a drain-source voltage (VDS) exceeding a pre-determined maximum value VDSmax, the bridging circuit automatically produce an inter-drain current flow between the drains of the first and second main switching FET thus limiting the maximum drain-source to VDSmax; wherein the bridging circuit further comprises a series connection of two opposing Zener diodes each having a Zener voltage of Vzx; and wherein said Vzx is selected to be slightly ≧2*V IN — MAX whereby clamps the maximum VDS to a value of about V IN — MAX +½ Vzx, wherein V IN MAX is a maximum DC supply voltage.