Integrated Darlington transistor combination including auxiliary transistor and Zener diode

Darlington transistor combination comprising an input transistor (T.sub.1), a driver transistor (T.sub.2) and a power transistor (T.sub.3), the respective collectors of said input and driver transistor being connected to the collector of said power transistor, the emitter of said input transistor being connected to the base of said driver transistor and the emitter of said driver transistor being connected to the base of said power transistor, the base of said input transistor being the control electrode of said transistor combination for connection of an input signal, and the collector and emitter of said power transistor providing the controlled path connection of said transistor combination, the base of said driver transistor (T.sub.2) being connected to a series circuit containing a first resistance (R.sub.4) connected to said driver transistor base and a Zener diode (ZD) having its anode connected to said first resistance (R.sub.4), a second resistance (R.sub.2) being connected in parallel to the base-emitter path of said driver transistor, said transistors, Zener diode, and first and second resistances being constituted as portions of an integrated circuit monolithically integrated by planar integrated circuit technology on a common semiconductor substrate which provides the collector zones of said transistors, the cathode of said Zener diode (ZD) being in circuit with the tap (15h) of a voltage divider consisting of a third resistance (R.sub.5,R.sub.6) and a fourth resistance (R.sub.7), said voltage divider having its ends respectively connected to the collector and emitter of said power transistor (T.sub.3), said transistor combination incorporating the improvement which comprises:

• an auxiliary transistor (T.sub.4) monolithically integrated on said common substrate and having its collector zone provided by said common substrate, coupled for conduction of the series circuit between said base of said driver transistor (T.sub.2) and the cathode of said Zener diode (ZD) under control of the potential of said tap (15h) of said voltage divider and having its collector connected to the collector of said power transistor by virtue of its said collector, like the collectors of the others of said transistors (T.sub.1, T.sub.2, T.sub.3), being provided by said common substrate, the base-emitter path of said auxiliary transistor (T.sub.4) being connected for receiving current flowing between said tap and said Zener diode cathode.