Bidirectional thyristor trigger circuit working principle diagram

Below is a detailed explanation of the two-way thyristor trigger circuit and its working principle. This voltage regulation circuit mainly consists of an RC phase shift network and a bidirectional thyristor (also known as a triac). These components are illustrated separately in the diagram above, with R5, RP, and C5 forming the RC phase shift circuit.

When the power switch S is turned on, the AC power supply charges capacitor C5 through resistors R5 and RP. As the voltage across C5 increases, it eventually reaches a level slightly higher than the breakover voltage of the bidirectional trigger diode ST. At this point, the ST triggers the triac VS, allowing current to flow through the load RL and powering it up.

During the zero-crossing point of the AC voltage, the triac automatically turns off. The capacitor C5 then begins to charge in the reverse direction, repeating the cycle. It's important to understand that this trigger circuit operates within an AC environment. The positive and negative half-cycles of the AC voltage send corresponding trigger pulses to the gate of the triac, ensuring symmetrical conduction during both cycles.

By adjusting the resistance value of RP, you can control the charging speed of C5, which in turn affects the conduction angle of the triac. This change in the conduction angle allows for precise control of the AC voltage applied to the load RL, effectively regulating the output voltage.

The diagram below illustrates the complete circuit setup, showing how the components interact to achieve smooth and stable voltage regulation. This type of circuit is commonly used in applications such as dimmer switches, motor speed controls, and temperature regulation systems.

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