What is a thyristor? How does it function?
1 Answer
A thyristor is a semiconductor device that belongs to the family of four-layer semiconductor devices known as "silicon-controlled rectifiers" (SCRs). It is a type of switch that can handle high currents and voltages and is widely used in power electronics applications. The thyristor has three terminals: anode, cathode, and gate. It can be triggered into conduction mode by a small current at the gate terminal.
Here's a brief explanation of how a thyristor functions:
Off State: Initially, the thyristor is in an off state, meaning that no current flows from the anode to the cathode.
Triggering: When a positive voltage pulse is applied to the gate terminal with respect to the cathode, it creates a small current flow at the gate. This current, also known as the gate trigger current (I_G), enables the thyristor to enter the conduction mode.
Conduction: Once the gate has been triggered, the thyristor enters the conduction state. At this point, the device starts to conduct current from the anode to the cathode, similar to a closed switch.
Latching: As the thyristor starts conducting, it becomes self-sustaining and remains in the conducting state even if the gate current is removed. This is known as latching, and it occurs because the internal junctions and the feedback mechanism of the device sustain the current flow.
Turn-off: To turn off the thyristor and return it to the off state, the anode current must be reduced below a threshold called the holding current (I_H). This holding current is typically lower than the gate trigger current. Alternatively, a reverse voltage across the thyristor (anode-cathode voltage in the reverse direction) can also turn it off.
Thyristors are commonly used in applications where high-power switching is required, such as motor control, lighting control, voltage regulation, and in various types of power converters. They are known for their ability to handle high currents, high voltage ratings, and their robustness in industrial and power electronics applications. However, one limitation is that they are unidirectional devices, meaning they can conduct current in one direction only (anode to cathode). For bidirectional control, two thyristors can be connected in an anti-parallel configuration.
Here's a brief explanation of how a thyristor functions:
Off State: Initially, the thyristor is in an off state, meaning that no current flows from the anode to the cathode.
Triggering: When a positive voltage pulse is applied to the gate terminal with respect to the cathode, it creates a small current flow at the gate. This current, also known as the gate trigger current (I_G), enables the thyristor to enter the conduction mode.
Conduction: Once the gate has been triggered, the thyristor enters the conduction state. At this point, the device starts to conduct current from the anode to the cathode, similar to a closed switch.
Latching: As the thyristor starts conducting, it becomes self-sustaining and remains in the conducting state even if the gate current is removed. This is known as latching, and it occurs because the internal junctions and the feedback mechanism of the device sustain the current flow.
Turn-off: To turn off the thyristor and return it to the off state, the anode current must be reduced below a threshold called the holding current (I_H). This holding current is typically lower than the gate trigger current. Alternatively, a reverse voltage across the thyristor (anode-cathode voltage in the reverse direction) can also turn it off.
Thyristors are commonly used in applications where high-power switching is required, such as motor control, lighting control, voltage regulation, and in various types of power converters. They are known for their ability to handle high currents, high voltage ratings, and their robustness in industrial and power electronics applications. However, one limitation is that they are unidirectional devices, meaning they can conduct current in one direction only (anode to cathode). For bidirectional control, two thyristors can be connected in an anti-parallel configuration.