Transformer coupled gate drive circuit for power MOSFETS

Claim 1

A driving circuit for a power transistor, comprising: a transformer having a primary winding responsive to an input control signal and a secondary winding for producing an output pulse having multiple control cycles wherein each control cycle comprises first and second sub-cycles; and a gate drive circuit coupled to the secondary winding of the transformer and effective for driving the power transistor; the gate circuit including: a first capacitor and a coupling device, connected between the first capacitor and the secondary winding, for coupling the first capacitor to the secondary winding; a first switching device connected between the first capacitor and a control electrode of the power transistor, in a manner which enables selective conduction of electrical charge from the first capacitor to the control electrode; a second switching device having one terminal connected to the control electrode of the power transistor and operable in a manner which enables the second switching device to selectively turn off the power transistor; and means for controlling the first and second switching devices; the transformer, the first capacitor and the first and second switching devices having such construction and being so connected, and the means for controlling the first and second switching devices being so effective, as to enable electrical charge to flow from the output pulse into the first capacitor essentially during the first sub-cycle and so as to activate the first switching device to conduct the electrical charge from the first capacitor to the control electrode of the power transistor, to turn on the power transistor during the second sub-cycle.