Transistor power switch control circuit - uses separate power and switching control transistors to reduce power losses in switching mode

摘要

The circuit has separate ON-OFF switching and power control using two control transistors (T2, T3) coupled to the base of the power transistor (T1). The control information is supplied to each control transistor (T2, T3) via a respective transformer (Tr1, Tr2), with a third transformer (Tr3) in the base circuit of the control transistor (T2) for ON-OFF switching, for amplification of the magnetisation current of the first transformer. The primary winding of the third transformer (Tr3) is coupled in series with a diode (D1) parallel to the secondary of the first transformer (Tr1), with the secondary of the third transformer (Tr3) parallel to the base-emitter path of a further transistor (T4). The collector of the latter is coupled to the base of the control transistor (T2) for ON-OFF switching, while its emitter is coupled to the terminal of the other control transistor (T3) which is not coupled to the power transistor base.