Driver circuit for energizing an electrical load in response to signals from a remote source

Claim 2

In a circuit for selectively coupling an electrical power supply (32) tO an electrical load (19) in response to a control signal, the combination comprising: a primary switching device (37) connected between said power supply and said load and having an open condition and a closed condition as determined by a control voltage applied to said primary switching device, an electrical resistance (41) having one end coupled to said power supply and having a circuit junction (42) at the opposite end, a signal detecting switching device (38) connected across said power supply through said circuit junction and electrical resistance and having means (27) for receiving said control signal, said signal detecting switching device being switchable between a conducting and nonconducting condition in response to said control signal whereby the voltage at said junction is changed while said control signal is present, circuit means (46) connected between said junction and said primary switching device for changing said control voltage applied thereto in response to said voltage change at said junction produced by said control signal, switch means (53) connected between said junction and said power supply in parallel relationship with said resistance, said switch means being of the form which becomes conductive only when a control voltage is applied thereto and remains conductive until the current flow therethrough is interrupted, and an overcurrent-sensing switching device (56) connected between said power supply and said switch means for applying said control voltage thereto in response to a predetermined degree of current increase at said primary switching device.

Claim 3

In a circuit as defined in claim 1, a second electrical resistance (48) connected between said power supply and said circuit means and wherein said circuit means derives said control voltage applied to said primary switching device through said second resistance, and wherein said overcurrent sensing switching device applies said control voltage to said switch means in response to a predetermined change of voltage drop across said second resistance.

Claim 4

A circuit for selectively coupling an electrical load (19) to a DC power supply (32) in response to a control signal, comprising a primary transistor (37) having an emitter-collector circuit connected between said power supply and said load and having a base, a first resistor (41), a signal detector transistor (38) having an emitter-collector circuit connected across said power supply through said first resistor, and having a base, means (27) for applying said control signal to said base of said signal detector transistor, a second resistor (48) a driver transistor (46) having an emitter-collector circuit connecting said base of said primary transistor with said power supply through said second resistor and having a base connected to said power supply through said first resistor whereby said driver transistor is biased to conductive state by the voltage change across said first resistor when said signal detector transistor becomes conductive upon receipt of said control signal, said conduction through said driver transistor biasing said primary transistor into conduction to energize said load, an SCR (53) connected between said power supply and said base of said driver transistor and having a control terminal, and an overcurrent-sensing transistor (56) having an emitter-collector circuit connected between said power supply and said control terminal of said SCR and having a base coupled to said power supply through said second resistor whereby said overcurrent-sensing transistor is biased into conduction by the voltage change across said second resistor produced by a predetermined decrease of impedance in said load, said conduction through said overcurrent-sensing resistor acting to trigger said SCR into conduction.

Claim 5

A circuit for selectively coupling an electrical load (19) to a DC power supply (32) in response to a control signal, comprising a primary transistor (37) having an emitter-collector circuit connected between said power supply and said load and having a base, a first resistor (41), a signal detector transistor (38) having an emitter-collector circuit connected across said power supply through said first resistor, and having a base, means (27) for applying said control signal to said base of said signal detector transistor, a second resistor (48) a driver transistor (46) having an emitter-collector circuit connecting said base of said primary transistor with said power supply through said second resistor and having a base connected to said power supply through said first resistor whereby said driver transistor is biased to conductive state by the voltage change across said first resistor when said signal detector transistor becomes conductive upon receipt of said control signal, said conduction through said driver transistor biasing said primary transistor into conduction to energize said load, an SCR (53) connected between said power supply and said base of said driver transistor and having a control terminal, and an overcurrent-sensing transistor (56) having an emitter-collector circuit connected between said power supply and said control terminal of said SCR and having a base coupled to said power supply through said second resistor whereby said overcurrent-sensing transistor is biased into conduction by the voltage change across said second resistor produced by a predetermined decrease of impedance in said load, said conduction through said overcurrent-sensing resistor acting to trigger said SCR into conduction.

Claim 6

The combination defined in claim 3 wherein said means for applying said control signal to the base of said signal detecting transistor Comprises a signal input conductor (27) coupled to said transistor base through a resistance capacitance network (43,44) for integrating an oscillating wave form to apply a relatively constant voltage to said transistor base during the duration of said control signal.

Claim 7

The combination defined in claim 3 further comprising a capacitor (58) connected between said control terminal of said SCR and said base of said driver transistor.

Claim 8

The combination defined in claim 3 further comprising a diode (57) connected between said base of said overcurrent-sensing transistor and said second resistor.