Control circuit for potential-free energising of power transistors - has transformer whose secondary is coupled to transistor emitter, as well as to control transistor collector, via diode

摘要

The power transistor has control line leads from a load circuit, via a transformer primary included in the load circuit. The transformer secondary (W2) is coupled to the control circuit. This transformer (Tr1) secondary is connected on one hand to the power transistor (T1) limitter, and on the other hand to the collector of a control transistor (T2), via a diode (D1). A control signal (UST1) is applied to the control transistor base-emitter terminal. The control transistor emitter is coupled to the power transistor base. A tertiary coil (W3) of opposite winding direction is connected on one hand to the power transistor base, via a series connection of a Zener diode (D2) and a further diode (D3) of opposite polarity. On the other hand it is connected to the transformer secondary coil end. A voltage source (U1) is shared both by control transistor collector and the power transistor emitter.