Abstract A DC coupled transistor turn-off circuit (12) responsive to a first DC voltage level for reverse driving the base of an output transistor (Q4), and responsive to a second DC voltage level for removing the reverse base drive. A turn-off transistor (Q5) is connected to the base (22) of the output transistor (Q4) for reverse driving it, and another transistor (Q6) is connected to the turn-off transistor (Q5) for turning it off. A pair of diodes (32, 34), each with different forward voltage drops, are connected between the respective bases of the turn-off circuit transistors (Q5, Q6) and a circuit input node (16). When the rising edge of the input voltage at such node reaches the first DC level, the first diode (32) conducts and activates the turn-off transistor (Q5) which reverse drives the base of the output transistor (Q4). On reaching a second higher DC voltage on the rising circuit node voltage, the second diode (34) conducts and turns off the turn-off transistor (Q5), thus removing the reverse drive of the output transistor (Q4).
A DC voltage level sensitive momentary turn-off circuit for use with an output transistor having at least a base, collector and emitter comprising: a first transistor having at least a base, collector and emitter with the collector connected to the base of the output transistor; a second transistor having at least a base, collector and emitter with the collector connected to the base of said first transistor and the emitter connected with the emitter of said first transistor; a first threshold means connected to the base of said first transistor and responsive to a first DC voltage level for activating said first transistor for applying reverse drive to the base of said output transistor; and a second threshold means connected to the base of said second transistor and responsive to a second DC voltage level different from said first DC level for subsequently activating said second transistor to thereby remove said reverse drive to said base of said output transistor.
Claim 2
Dependent Claim
160 words
A DC voltage level sensitive momentary turn-off circuit for use with an output transistor having at least a base, collector and emitter comprising: a first transistor having at least a base, collector and emitter with the collector connected to the base of the output transistor; a second transistor having at least a base, collector and emitter with the collector connected to the base of said first transistor and the emitter connected with the emitter of said first transistor; a first threshold means connected to the base of said first transistor and responsive to a first DC voltage level for activating said first transistor for applying reverse drive to the base of said output transistor; and a second threshold means connected to the base of said second transistor and responsive to a second DC voltage level different from said first DC level for subsequently activating said second transistor to thereby remove said reverse drive to said base of said output transistor.
Claim 3
Dependent Claim
54 words
The turn-off circuit of claim 1 wherein said first threshold means comprises a first diode with a selected voltage thereacross when conductive, and said second threshold means comprises a second diode with a voltage thereacross when conductive, the selected voltage of said second diode being higher than said selected voltage of said first diode.
Claim 4
Dependent Claim
45 words
The turn-off circuit of claim 2 wherein said first diode is a Schottky-type diode with its cathode connected to the base of said first transistor, and said second diode is a PN junction-type diode with its cathode connected to the base of said second transistor.
Claim 5
Dependent Claim
22 words
The turn-off circuit of claim 3 and further including a resistor connected between the base and the emitter of said second transistor.