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A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor [1]) is a three-terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised trademark.
A zero-cross circuit works to correct this problem, so that the TRIAC functions as well as possible. This is typically done with thyristors in two of the three phases. Many opto-TRIACs come with zero-cross circuits built in. They are often used to control larger, power TRIACs.
In AC circuits, SCR or triac relays inherently switch off at the points of AC zero cross when there is zero load current. The circuit will never be interrupted in the middle of a sine wave peak, preventing the large transient voltages that would otherwise occur due to the sudden collapse of the magnetic field around the inductance.
If no current/voltage is applied to the gate lead, the TRIAC switches off. On the other hand, if the trigger voltage is applied to the gate lead, the TRIAC switches on. TRIACs are suitable for light-dimming circuits, phase-control circuits, AC power-switching circuits, AC motor control circuits, etc.
One example is the TRIAC, which is comparable to two thyristors connected back-to-back (in other words, reverse parallel), but on a single piece of silicon. Two LEDs can be paired this way, so that each protects the other from reverse voltage. A series string of such pairs can be connected to AC or DC power, with an appropriate resistor.
A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics (for example in a switch-mode power supply).Such a device is also called a power device or, when used in an integrated circuit, a power IC.
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 ( phase control ).
A solid-state relay uses a thyristor, TRIAC or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-emitting diode (LED) coupled with a photo transistor ) can be used to isolate control and controlled circuits.
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