Abstract: In a base drive circuit for a high power transistor, an external signal is applied to the circuit by an optical coupler. In response to the external signal, the circuit provides a positive current to the high power transistor in order turn it on. The positive constant current is characterized by an initial spike that prevents any localized hot spots from developing in the high power transistor and thereafter the positive current becomes constant. The circuit also provides a constant negative current when the external signal is removed, thereby quickly turning off the high power transistor. The optical coupler and a time delay device provide the circuit with high noise immunity.