Darlington transistor circuit

Darlington transistor circuit for switching of an inductive load (ZS) having

• a current supply voltage source;
• a power transistor (T.sub.3);
• a driver transistor (T.sub.2), the collector of the power transistor (T.sub.3) and the collector of the driver transistor (T.sub.2) being connected together, the base of the power transistor (T.sub.3) and the emitter of the driver transistor (T.sub.2) being connected together;
• an initial transistor (T.sub.1), the collector of the initial transistor (T.sub.1) being connected to the collector of the power transistor (T.sub.3), the emitter of the initial transistor (T.sub.2) being connected to the base of the driver transistor (T.sub.2);
• means (T.sub.0) providing an input trigger signal to the base of the initial transistor (T.sub.1),
• said Darlington transistor circuit comprising
• a series circuit including a voltage divider comprising
• a first resistor (R.sub.1) and a second resistor (R.sub.2) forming the voltage divider, and having a tap or junction point between the first and second resistor, the tap or junction point being connected to the base of the driver transistor (T.sub.2),
• said series circuit further including a Zener diode (ZD),
• the terminal of the first resistor (R.sub.1) remote from the tap or junction point being connected to the anode of the Zener diode (ZD), the cathode of the Zener diode being connected to a terminal (B+) of the current supply voltage source through the inductive load,
• the terminal of the second resistor (R.sub.2) remote from the tap or junction point being connected to the emitter of the driver transistor (T.sub.2),
• so that the second resistor (R.sub.2) will be connected in parallel across the base-emitter path of the driver transistor,
• and wherein the ratio of resistances of the first (R.sub.1) and the second (R.sub.2) resistors is selected in accordance with a selected temperature/turn-ON voltage relationship at the cathode of the Zener diode (ZD).