Power transistor drive apparatus in a DC-converter

Claim 1

Power transistor drive apparatus in a DC-converter, said converter having first and second terminals for respective connection to the terminals of a DC supply voltage, a main transformer means, rectifying means and filtering means, said power transistors being alternately conducting and each having a main current circuit connected to said main transformer means and a control current circuit, comprising a first and a second drive transistor, a first and a second drive transformer each consisting of a primary winding connected to one of said terminals via one of said drive transistors and at least one secondary winding connected to the control current circuit of said power transistors, a further transformer consisting of a first and a second winding connected to said main current circuit of each of the power transistors, an a third winding connected to one of the primary windings of said first and second drive transformers for transferring, via said first winding and one of said drive transformers, a current proportional to the current through the main current circuit of one of said power transistors to the control circuit of the same transistor and, at the same time, for creating a voltage drop across said secondary winding which counteracts conducting of the non-conducting power transistor, and a first and a second capacitor connected to the primary winding of said first and second drive transformer and to one of said terminals, said capacitors each being charged via the third winding of said further transformer when the associated power transistor is conducting and being discharged when the same transistor is non-conducting, whereby the capacitor voltage provides further blocking of the transistor.