Thyristor is a semiconductor device that is widely used in power electronics applications. It is a type of switch that can be turned on and off using a control signal. There are different types of thyristors available, each with its own unique characteristics.

Unilateral and Bistable

One type of thyristor is the unilateral and bistable thyristor. This means that the device can conduct current in only one direction and has two stable states: on and off. The device remains in the same state until a control signal is applied to change its state.

Working Principle

The working principle of a thyristor is based on the behavior of the P-N junctions within the device. The device consists of four layers of alternating P and N-type semiconductor material. The three terminals of the device are the anode, cathode, and gate.

When a positive voltage is applied to the anode, the P-N junctions become forward-biased, allowing current to flow through the device. However, the device remains in the off state until a positive voltage is applied to the gate terminal.

When a positive voltage is applied to the gate terminal, a small amount of current flows through the gate-cathode junction, triggering the device to turn on. Once turned on, the device remains in the on state even if the gate voltage is removed. The only way to turn off the device is to reverse the voltage across the anode-cathode terminals or to reduce the current below a certain threshold level.

Applications

Thyristors are widely used in power electronics applications such as motor control, AC power control, and DC power supplies. They are also used in voltage regulators, inverters, and other electronic circuits that require high current and voltage switching capabilities.