Thermal protective system utilizing fault-responsive shunt means for a normally conducting triac

Claim 2

A protective system for controlling the supply of power to a load in response to variations in a preselected environmental parameter comprising an AC power switch means comprising a triac having a pair of power terminals and a control element comprising a gate adapted to control the conduction thereof, means including a rectifier diode for supplying DC trigger signals coupled to said gate for controlling the conduction of said triac, a selectively energizable load serially connected to said AC power switch means, means for coupling said load to an AC power source to supply power thereto only when the AC power switch means is rendered conductive by the DC control signal, a selectively energizable unidirectional switch means which comprises a siliconcontrolled rectifier, coupled to the means for supplying the DC trigger signals and to said control element for selectively shunting the DC control signal through said unidirectional switch means when said unidirectional switch means is conductive to render said AC switch means nonconductive, said unidirectional switch means having a control element for controlling the conduction thereof, said control element of said unidirectional switch means comprising the gate thereof, a sensor comprising a thermistor, the resistance of said sensor varying in response to variations in the environmental parameter, and means for electrically coupling said sensor to said control element of said unidirectional switch means in a manner so that variations in the resistance of said sensor effect corresponding changes in the conduction of said unidirectional switch means, thereby controlling the conduction of said AC power switch means, said means for electrically coupling said sensor to said control element of said unidirectional switch means including a voltage divider having a first resistor and a second resistor with a junction therebetween said first resistor of said voltage divider being coupled to the power supply means and to said gate of said triac, said siliconcontrolled rectifier having its gate coupled to said voltage divider junction and having its anode-cathode circuit coupled to said gate of said triac for selectively shunting DC trigger signals from said triac gate, and said sensor being connected to one of said first and second resistors so as to vary the voltage level at said voltage divider junction in response to variations in the environmental parameter.

Claim 3

A protective system in accordance with claim 1 wherein said silicon-controlled rectifier having its anode-cathode circuit connected across said voltage divider, and a voltage-responsive means comprising a Zener diode coupled between said voltage divider junction and said gate of said silicon-controlled rectifier, said voltage-responsive means being adapted to supply an electrical signal to said gate sufficient to render said silicon-controlled rectifier substantially instantaneously conductive and thereby shunt DC trigger signals from said triac gate.

Claim 4

A substantially transient insensitive protective system for selectively disrupting the supply of power to a load in response to sensed variations in an environmental parameter comprising a triac having a gate and a pair of power terminals, means coupled to said gate for supplying DC trigger signals thereto so as to control the conduction of said triac, means for connecting a selectively energizable load in series with said power terminals, the load being supplied with AC power only when said triac is in a conductive state, a selectively energizable unidirectional switch means coupled to said means for supplying DC trigger signals and to said gate of said triac said unidirectional switch means comprising a silicon-controlled rectifier and including a shunt circuit, said shunt circuit comprising the anode-cathode circuit of said silicon-controlled rectifier and being electrically connected in parallel relationship with said means for supplying DC trigger signals and said gate of said triac for selectively shunting DC trigger signals from said gate of said triac through said unidirectional switch means when said unidirectional switch means is conductive, a control element comprising the gate of said silicon-controlled rectifier for controlling the conduction of said unidirectional switch means, a voltage divider including a first resistor, a second resistor, and a common junction therebetween, a sensor having a resistance which varies in response to variations in the environmental parameter coupled to one of said resistors of said voltage divider, said sensor comprising a thermistor adapted to sense changes in temperature and having a resistance which increases in response to an increase in sensed temperature, voltage-responsive means comprising a Zener diode for coupling said control element to said voltage divider junction to preclude the flow of transient signals sufficient to affect the conduction of said switch means and means for establishing a first preselected voltage level at said voltage divider junction in response to a first condition of the environmental parameter and for establishing a second preselected voltage level at said voltage divider junction in response to a second condition of the environmental parameter, said second preselected voltage level being sufficient to render said unidirectional switch means conductive, thereby shunting DC trigger signals through said shunt circuit to render said triac nonconductive and disrupt the AC power to the load.

Claim 5

A substantially transient insensitive protective system for selectively disrupting the supply of power to a load in response to sensed variations in an environmental parameter comprising a triac having a gate and a pair of power terminals, means coupled to said gate for supplying DC trigger signals thereto so as to control the conduction of said triac, means for connecting a selectively energizable load in series with said power terminals, the load being supplied with AC power only when said triac is in a conductive state, a selectively energizable unidirectional switch means coupled to said means for supplying DC trigger signals and to said gate of said triac said unidirectional switch means comprising a silicon-controlled rectifier and including a shunt circuit, said shunt circuit comprising the anode-cathode circuit of said silicon-controlled rectifier and being electrically connected in parallel relationship with said means for supplying DC trigger signals and said gate of said triac for selectively shunting DC trigger signals from said gate of said triac through said unidirectional switch means when said unidirectional switch means is conductive, a control element comprising the gate of said silicon-controlled rectifier for controlling the conduction of said unidirectional switch means, a voltage divider including a first resistor, a second resistor, and a common junction therebetween, a sensor having a resistance which varies in response to variations in the environmental parameter coupled to one of said resistors of said voltage divider, said sensor comprising a thermistor adapted to sense changes in temperature and having a resistance which increases in response to an increase in sensed temperature, voltage-responsive means comprising a Zener diode for coupling said control element to said voltage divider junction to preclude the flow of transient signals sufficient to affect the conduction of said switch means and means for establishing a first preselected voltage level at said voltage divider junction in response to a first condition of the environmental parameter and for establishing a second preselected voltage level at said voltage divider junction in response to a second condition of the environmental parameter, said second preselected voltage level being sufficient to render said unidirectional switch means conductive, thereby shunting DC trigger signals through said shunt circuit to render said triac nonconductive and disrupt the AC power to the load.

Claim 6

A protective system for controlling the supply of power to a load in response to variations in a preselected environmental parameter comprising an AC power switch means having a pair of power terminals and having a control element adapted to control the conduction thereof, means for supplying DC power including a rectifier diode coupled to said gate for supplying DC trigger signals to said gate for controlling the conduction of said triac, a selectively energizable load serially connected to said AC power switch means, means for coupling said load to an AC power source when said AC power switch means is conductive, a selectively energizable unidirectional switch means coupled to the DC power supply means comprising a transistor having a base for controlling its conduction and having its emitter-collector circuit couplEd to said control element for selectively shunting DC trigger signals therefrom when said unidirectional switch means is conductive, a sensor comprising a thermistor having a positive temperature coefficient of resistance, the resistance of said thermistor varying in response to variations in the environmental parameter, and means for electrically coupling said sensor to said control element of said unidirectional switch means including a voltage divider having a first resistor and a second resistor with a junction therebetween, said first resistor being coupled to the power supply means and to said control element of said AC power switch means, said junction being coupled to said control element of said unidirectional control element, one of said first and second resistors being connected to said sensor so as to vary the voltage level at said junction in response to variations in the environmental parameter, and a voltage-responsive means comprising a silicon unilateral switch connected between said voltage divider junction and the base of said transistor, said silicon unilateral switch being adapted to supply an electrical signal to said base sufficient to effect conduction of said transistor at a saturation level substantially instantaneously in response to the establishment of a preselected voltage level at said voltage divider junction so as to shunt DC trigger signals from said control element of said AC power switch means so that variations in the electrical resistance of said thermistor in response to sensed changes in environmental temperature effect corresponding variations in the conduction of said unidirectional switch means, thereby controlling the conduction of said AC power switch means.

Claim 7

A protective system for controlling the supply of power to a load in response to variations in a preselected environmental parameter comprising an AC power switch means having a pair of power terminals and having a control element adapted to control the conduction thereof, means for supplying DC power including a rectifier diode coupled to said gate for supplying DC trigger signals to said gate for controlling the conduction of said triac, a selectively energizable load serially connected to said AC power switch means, means for coupling said load to an AC power source when said AC power switch means is conductive, a selectively energizable unidirectional switch means coupled to the DC power supply means comprising a transistor having a base for controlling its conduction and having its emitter-collector circuit couplEd to said control element for selectively shunting DC trigger signals therefrom when said unidirectional switch means is conductive, a sensor comprising a thermistor having a positive temperature coefficient of resistance, the resistance of said thermistor varying in response to variations in the environmental parameter, and means for electrically coupling said sensor to said control element of said unidirectional switch means including a voltage divider having a first resistor and a second resistor with a junction therebetween, said first resistor being coupled to the power supply means and to said control element of said AC power switch means, said junction being coupled to said control element of said unidirectional control element, one of said first and second resistors being connected to said sensor so as to vary the voltage level at said junction in response to variations in the environmental parameter, and a voltage-responsive means comprising a silicon unilateral switch connected between said voltage divider junction and the base of said transistor, said silicon unilateral switch being adapted to supply an electrical signal to said base sufficient to effect conduction of said transistor at a saturation level substantially instantaneously in response to the establishment of a preselected voltage level at said voltage divider junction so as to shunt DC trigger signals from said control element of said AC power switch means so that variations in the electrical resistance of said thermistor in response to sensed changes in environmental temperature effect corresponding variations in the conduction of said unidirectional switch means, thereby controlling the conduction of said AC power switch means.

Claim 8

A substantially transient insensitive protective system for selectively disrupting the supply of power to a load in response to sensed variations in an environmental parameter comprising a triac having a gate and a pair of power terminals, means coupled to said gate for supplying DC trigger signals thereto so as to control the conduction of said triac, means for connecting a selectively energizable load in series with said power terminals, the load being supplied with AC power only when said triac is in a conductive state, a selectively energizable unidirectional switch means comprising a transistor coupled to said means for supplying DC trigger signals and to said gate of said triac, the collector-emitter circuit of said transistor comprising a shunt circuit electrically connected in parallel relationship with said means for supplying DC trigger signals and said gate of said triac for selectively shunting DC trigger signals from said gate of said triac when said unidirectional switch means is conductive, the base of said transistor comprising a control element for controlling the conduction of said switch means, a voltage divider including a first resistor, a second resistor, and a common junction therebetween, a sensor comprising a thermistor adapted to sense temperature changes and having a resistance which increases in response to an increase in sensed environmental temperature coupled to one of said resistors of said voltage divider, voltage-responsive means comprising a silicon unilateral switch for coupling said control element to said voltage divider junction to preclude the flow of transient signals sufficient to affect the conduction of said switch means, and means for establishing a first preselected voltage level at said voltage divider junction in response to a first condition of the environmental parameter and for establishing a second preselected voltage level at said voltage divider junction in response to a second condition of the environmental parameter, said second preselected voltage level being sufficient to render said switch means conductive, thereby shunting DC trigger signals through said shunt circuit to render said triac nonconductive and disrupt the AC power to the load.

Claim 9

A substantially transient insensitive protective system for selectively disrupting the supply of power to a load in response to sensed variations in an environmental parameter comprising a triac having a gate and a pair of power terminals, means coupled to said gate for supplying DC trigger signals thereto so as to control the conduction of said triac, means for connecting a selectively energizable load in series with said power terminals, the load being supplied with AC power only when said triac is in a conductive state, a selectively energizable unidirectional switch means comprising a transistor coupled to said means for supplying DC trigger signals and to said gate of said triac, the collector-emitter circuit of said transistor comprising a shunt circuit electrically connected in parallel relationship with said means for supplying DC trigger signals and said gate of said triac for selectively shunting DC trigger signals from said gate of said triac when said unidirectional switch means is conductive, the base of said transistor comprising a control element for controlling the conduction of said switch means, a voltage divider including a first resistor, a second resistor, and a common junction therebetween, a sensor comprising a thermistor adapted to sense temperature changes and having a resistance which increases in response to an increase in sensed environmental temperature coupled to one of said resistors of said voltage divider, voltage-responsive means comprising a silicon unilateral switch for coupling said control element to said voltage divider junction to preclude the flow of transient signals sufficient to affect the conduction of said switch means, and means for establishing a first preselected voltage level at said voltage divider junction in response to a first condition of the environmental parameter and for establishing a second preselected voltage level at said voltage divider junction in response to a second condition of the environmental parameter, said second preselected voltage level being sufficient to render said switch means conductive, thereby shunting DC trigger signals through said shunt circuit to render said triac nonconductive and disrupt the AC power to the load.

Claim 10

A protEctive system in accordance with claim 5 wherein said transistor comprises an NPN transistor, having its base-emitter circuit connected across said sensor and said one resistor of said voltage divider in a manner so that a preselected increase in the resistance of said sensor establishes a sufficient forward bias across the base-emitter circuit to render said NPN transistor conductive.