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Thyristors are a type of electronic component that can be used to both control and switch electronic current and are classified as either unidirectional or bidirectional components depending on the direction of the electrical current that passes through them. In this article, we will focus on TRIACs, which are a type of bidirectional thyristors, and explore their application field and working principle.

What is a TRIAC?

A TRIAC – The TRIode for AC – is a type of bidirectional thyristor which is characterised by its three terminals, named main terminal (1), gate (2) and anode (3) or also named MT1, G and MT2 respectively. A TRIAC is a controllable two-terminal device, one terminal connected to gate is used to control the flow of electric current through the two other terminals. TRIACs are widely used to switch or control electrical and electronic devices with AC currents due to its ability to “turn on”, “hold on”, and “turn off” based on an applied voltage or current.

Application field

Due to its high AC current control ability, TRIACs can be used for a wide range of applications. First and foremost, TRIACs are massively used to control electronic items like motor speed controls, lighting control circuits and dimmers etc. For example, when a motor speed is need to be adjustable, TRIACs can help regulate the voltage flow passing through the motor, thus controlling the speed. Likewise, a TRIAC is used in lighting control systems to adjust the brightness of lights by controlling the current passing through them.

Additionally, TRIACs are also the preferred choice for motor control in small power applications. These applications employ TRIACs in order to regulate the current going through the motor, thus controlling the speed or position of machines or engines. Lastly, TRIACs are also found as critical components in communication systems, SCR controllers, board mounted controllers and microwave ovens as well.

Working principles of a TRIAC

A TRIAC works in accordance to thepn junction physical effect. When a TRIAC is enabled, current flows through the MT1 and MT2 terminals in alternating direction while no current passes through the gate terminal. This current flow occurs due to the presence of a pn junction formed between the eletrode-gate and anode-cathode .

TRIACs are switches which are opened by a small reversing gate potential. This gate potential will reverse the resistance of the gate terminal, thus ‘opening’ the TRIAC, interrupting the current flow between the MT1 and MT2 terminals. Thus, the amount of current that can pass through the TRIAC is controlled by the gate potential.

Moreover, the run and ‘off’ state of a TRIAC can also be controlled by the gate. The current flow across the TRIAC can be changed depending on if a gate-controlled TRIAC is utilized as when the gate current is increased, the current across the anode-cathode junction is increased as well thus, increasing the amount of current passing through the TRIAC.

Conclusion

In conclusion, TRIACs are a type of two-terminal bidirectional thyristor which is highly versatile and used to switch and control AC currents. TRIACs are used in various applications such as motor speed control, lighting control and board mounted controllers, among many others. Moreover, the TRIAC works in accordance to the pn junction physical effect, where the run and ‘off’ state of a TRIAC is determined by the gate potential and current.

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