Abstract: An improved proportional base drive circuit for rapidly and efficiently switching a high current bipolar transistor includes a transformer having first and second serially connected windings coupled in a load current path between the emitter terminal of the transistor and a load. A base terminal of the transistor is connected to a junction intermediate the two windings by a base bias circuit. The turns ratio between the two windings is selected to force a proportional base current to flow to the transistor. A third winding is provided, along with switching apparatus for exciting the third winding, whereby conduction of the load transistor can be initiated by energizing the third winding. A diverter circuit connected to the third winding allows rapid removal of current from the base of the load transistor for fast turn-off. In an alternative embodiment, a fourth winding is arranged to provide a driving current for more rapid forcing of current from the base drive circuit at turn-off.