NationMaster - Encyclopedia: Triac

A TRIAC, or TRIode for Alternating Current is an electronic component approximately equivalent to two silicon-controlled rectifiers (SCRs/thyristors) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. This results in a bidirectional electronic switch which can conduct current in either direction when it is triggered (turned on). It can be triggered by either a positive or a negative voltage being applied to its gate electrode. Once triggered, the device continues to conduct until the current through it drops below a certain threshold value, such as at the end of a half-cycle of alternating current (AC) mains power. This makes the TRIAC a very convenient switch for AC circuits, allowing the control of very large power flows with milliampere-scale control currents. In addition, applying a trigger pulse at a controllable point in an AC cycle allows one to control the percentage of current that flows through the TRIAC to the load (so-called phase control). Image File history File links Triac. ... Image File history File links Triac. ... This article is about the engineering discipline. ... SCR schematic symbol A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a 4-layer solid state device that controls current flow. ... Circuit symbol for a thyristor The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. ... Two antiparallel molecules run side-by-side in opposite directions. ... Electric current is by definition the flow of electric charge. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... City lights viewed in a motion blurred exposure. ... In physics, the ampere (symbol: A, often informally abbreviated to amp) is the SI base unit used to measure electrical currents. ...

Low power TRIACs are used in many applications such as light dimmers, speed controls for electric fans and other electric motors, and in the modern computerized control circuits of many household small and major appliances. However, when used with inductive loads such as electric fans, care must be taken to assure that the TRIAC will turn off correctly at the end of each half-cycle of the ac power. Most of the industrialized world is lit by electric lights, which are used both at night and to provide additional light during the daytime. ... Dimmers are devices used to vary the control the brightness of a light. ... Household Electric Fan A fan has two purposes. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils An electric motor converts electrical energy into mechanical energy. ... Electric egg beater Small appliance refers to a class of home appliances that are semi-portable or which are used on tabletops, countertops, or other platforms. ... A major appliance is a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, food preservation, or cleaning, whether in a household, institutional, commercial or industrial setting. ... An inductor is a passive electrical device employed in electrical circuits for its property of inductance. ...

Triac semiconductor construction

A snubber circuit is often used to assist this turn off. Snubber circuits are also used to prevent premature triggering. For higher-powered, more-demanding loads, two SCRs in inverse parallel may be used instead of one TRIAC. Because each SCR will have an entire half-cycle of reverse polarity voltage applied to it, turn-off of the SCRs is assured, no matter what the character of the load. Image File history File links Trix. ... Image File history File links Trix. ... A snubber is a simple electrical circuit used to suppress (snub) electrical transients. ...

External links

A site about thyristors

Categories: Solid state switches | Power electronics

Results from FactBites:

Triacs (266 words)
	The triac can be triggered by a gate-trigger pulse which is either positive or negative with respect to main terminal No.1 when main terminal No.2 is either positive or negative with respect to main terminal No. 1.
	The triac, therefore, can be triggered in any of four operating modes, as summarized in Table I. The quadrant designations refer to the operating quadrant on the principal voltage-current characteristics (either I or III), and the polarity symbol represents the gate-to-main-terminal-No. 1 voltage.
	For RCA triacs, the maximum trigger-current rating in the published data is the largest value of gate current that is required to trigger the selected device in any operating mode.

Control circuit for hospital bed - Patent 4044286 (5990 words)
	Gating of the gating triacs is achieved by an appropriate switching arrangement, which obtains a gating signal for the gating triacs from the secondary winding of the power transformer.
	The number of power triacs employed will depend, of course, upon the number of functions to be achieved, but as this preferred embodiment relates to a bed having three movable portions, each of which is positionable in two directions, a total of six power triacs are employed.
	The first terminals of triacs 35 and 36 are connected to the neutral side 25 of plug 21, while the first terminals of triacs 37-40 are connected to the hot side 23 of plug 21.

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