Zero voltage firing proportional controller

Claim 2

In a controller of the class wherein the firing of a triac is controlled by output pulses generated by a zero-voltage switch as an ac line voltage passes through zero, the improvement comprising first means normally preventing the zero-voltage switch from generating output pulses on negative half-cycles of the line voltage, second means rendering the first means ineffective only if the triac has been previously fired on a positive half-cycle of the line voltage, and third means causing the zero-voltage switch to generate an output pulse on the immediately following negative half-cycle of the line voltage.

Claim 3

A proportional temperature controller energizable by an ac power line and comprising, a. a temperature sensor, b. means producing a voltage which varies in magnitude with temperature changes of said sensor, c. a zero-voltage switch responsive to said voltage, said switch generating output pulses during each passage of the line vOltage through zero, d. means developing a phase-shifted inhibit voltage during each positive half-cycle of the line voltage, e. circuit elements applying the said inhibit voltage to the zero-voltage switch, said inhibit voltage normally preventing the switch from generating output pulses on negative half-cycles of the line voltage, f. a load connected to the power line through a thyristor, g. means firing the thyristor in response to said output pulses, h. means clamping the inhibit voltage only if the thyristor has been previously fired on a positive half-cycle of the line voltage, and i. means applying an unbalancing voltage to the zero-voltage switch when the inhibit voltage is clamped, said unbalancing voltage causing said switch to generate an output pulse on the immediately following negative half-cycle of the line voltage.

Claim 4

A proportional temperature controller energizable by an ac power line and comprising, a. a temperature sensor, b. means producing a voltage which varies in magnitude with temperature changes of said sensor, c. a zero-voltage switch responsive to said voltage, said switch generating output pulses during each passage of the line vOltage through zero, d. means developing a phase-shifted inhibit voltage during each positive half-cycle of the line voltage, e. circuit elements applying the said inhibit voltage to the zero-voltage switch, said inhibit voltage normally preventing the switch from generating output pulses on negative half-cycles of the line voltage, f. a load connected to the power line through a thyristor, g. means firing the thyristor in response to said output pulses, h. means clamping the inhibit voltage only if the thyristor has been previously fired on a positive half-cycle of the line voltage, and i. means applying an unbalancing voltage to the zero-voltage switch when the inhibit voltage is clamped, said unbalancing voltage causing said switch to generate an output pulse on the immediately following negative half-cycle of the line voltage.

Claim 5

A proportional temperature controller energizable by an ac power line and comprising, a. a temperature sensor having a negative temperature coefficient of resistance, b. a zero-voltage switch responsive to changes in the resistance of said sensor, said switch generating output pulses during each passage of the line voltage through zero, c. means developing a phase-shifted inhibit voltage during each positive half-cycle of the line voltage, d. circuit elements applying the said inhibit voltage to the zero-voltage switch, said voltage normally preventing the switch from generating output pulses on negative half-cycles of the line voltage, e. a load connected to the power line through a triac, f. means firing the triac in response to said output pulses, g. means clamping the inhibit voltage only if the triac has been previously fired on a positive half-cycle of the line voltage, and h. means applying an unbalancing voltage to the zero-voltage switch when the inhibit voltage is clamped, said unbalancing voltage causing said switch to generate an output pulse on the immediately following negative half-cycle of the line voltage.

Claim 6

A proportional temperature controller energizable by an ac power line and comprising, a. a temperature sensor having a negative temperature coefficient of resistance, b. a zero-voltage switch responsive to changes in the resistance of said sensor, said switch generating output pulses during each passage of the line voltage through zero, c. means developing a phase-shifted inhibit voltage during each positive half-cycle of the line voltage, d. circuit elements applying the said inhibit voltage to the zero-voltage switch, said voltage normally preventing the switch from generating output pulses on negative half-cycles of the line voltage, e. a load connected to the power line through a triac, f. means firing the triac in response to said output pulses, g. means clamping the inhibit voltage only if the triac has been previously fired on a positive half-cycle of the line voltage, and h. means applying an unbalancing voltage to the zero-voltage switch when the inhibit voltage is clamped, said unbalancing voltage causing said switch to generate an output pulse on the immediately following negative half-cycle of the line voltage.

Claim 7

The invention as recited in claim 3 wherein the said means clamping the inhibit voltage comprises a transistor having output electrodes connected across the inhibit voltage and a base energized by the output pulses of the zero-voltage switch through a phase-shifting network.

Claim 8

The invention as recited in claim 4, wherein the said unbalancing voltage is in phase with the energizing voltage applied to the base of said transistor.