Trigger circuit

Claim 1

An electronic trigger circuit for uncoupling an inductive load from a pair of power-input terminals connectable to a DC voltage source in response to application of a predetermined minimum voltage at a signal-input terminal, said trigger circuit comprising: a. a first transistor having collector, base and emitter electrodes, the collector electrode being coupled through said inductive load to the positive power-input terminal, the emitter electrode being coupled to the negative power-input terminal, and the base electrode being coupled through a resistance to the positive power-input terminal to bias said first transistor conductive when a DC voltage is applied across the power-input terminals; b. a second transistor having base emitter and collector electrodes, the base electrode being coupled to said signal input terminal And through a capacitor to the negative powerinput terminal, the emitter electrode being coupled to the negative power-input terminal, and the collector electrode being coupled to the base electrode of said first transistor, said second transistor being normally in a nonconductive state when a DC voltage is applied across the power-input terminals and being adapted to switch to a conductive state to bias said first transistor to a nonconductive state in response to a predetermined minimum voltage being applied to the signal-input terminal; and c. a diode having anode and cathode terminals, the anode terminal being coupled to the collector electrode of said first transistor, and the cathode being electrically coupled to the base electrode of said second transistor to provide a feedback path for opposing emf developed by the inductive load when said first transistor is rendered nonconductive to prevent said first transistor from being switched back to its conductive state by said opposing emf.