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Triac Gate Control Circuit

IP.com Disclosure Number: IPCOM000074946D
Original Publication Date: 1971-Jul-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Beistle, RG: AUTHOR

Abstract

This gate control circuit fires an AC energized triac at zero-crossover such that the triac operates as an AC contactor. An R-C network provides DV/DT protection for the triac and controls the triac firing voltage.

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Triac Gate Control Circuit

This gate control circuit fires an AC energized triac at zero-crossover such that the triac operates as an AC contactor. An R-C network provides DV/DT protection for the triac and controls the triac firing voltage.

A bidirectional gate controlled rectifier 1, such as a triac, is connected in series with load 2 to a source of alternating current 3. Conduction of the rectifier is controlled by switch 4. When this switch is open, the rectifier conducts and the load is energized. When the switch is closed, the rectifier does not conduct and the load is deenergized. The switch is exposed to the low-level firing voltage of the rectifier, thus eliminating voltage breakdown problems.

Resistor 5 and capacitor 6 are selected to provide DV/DT suppression upon the closing of the switch to deenergize the load. Capacitor 7 is selected in accordance with the required rectifier gate voltage and current The capacitance value of capacitor 6 should be greater than the value of capacitor 7 to insure firing of the rectifier early in each AC half-cycle. Capacitor 7 charges to the breakover voltage of bidirectional breakdown device 8, such as a neon lamp, and this capacitor then discharges through the gate to fire the rectifier.

Fig. 2. discloses the use of a unidirectional switch, such as light-sensitive transistor 11, which is connected in circuit with a diode bridge and can be used to replace bidirectional switch 4 of Fig. 1.

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