An article to understand the structure and conductive properties of unidirectional thyristors

Thyristor is the abbreviation of thyristor, also known as thyristor rectifier, formerly referred to as thyristor; in 1957, General Electric Company of the United States developed the world’s first thyristor product, and in 1958 its commercialization.

Thyristor is the abbreviation of thyristor, also known as thyristor rectifier, formerly referred to as thyristor; in 1957, General Electric Company of the United States developed the world’s first thyristor product, and in 1958 its commercialization.

Thyristor is NPNP four-layer semiconductor structure, it has three poles: anode, cathode and control pole; thyristor has the characteristics of silicon rectifier device, can work under high voltage and high current conditions, and its working process can be controlled and is widely used in In Electronic circuits such as controllable rectification, AC voltage regulation, contactless electronic switch, inverter and frequency conversion.

Thyristors can be divided into ordinary thyristors, bidirectional thyristors, reverse conducting thyristors, gate turn-off thyristors (GTO), BTG thyristors, temperature-controlled thyristors and light-controlled thyristors according to their off, on and control methods. Let’s take a closer look at the structure and conductive properties of unidirectional thyristors.

Symbol and internal structure of unidirectional thyristor

The unidirectional thyristor consists of an NPNP four-layer semiconductor with three PN junctions formed in the middle. There are three electrodes, namely anode A, cathode K, and gate G (also called control electrode).

An article to understand the structure and conductive properties of unidirectional thyristors

Conductive properties of unidirectional thyristors

In the circuit shown in the figure below, when the switch S1 is closed, the gate G has no trigger voltage, so the thyristor is in the off state, and the light bulb will not be lit.

As shown in the figure below, when S2 is closed, the gate G is subjected to the trigger voltage, the thyristor is turned on, and the bulb is lit.

As shown in the figure below, when the thyristor gate G is triggered and the thyristor is turned on, even if the trigger voltage of the gate G is removed, the thyristor will remain on, that is, after the thyristor is turned on, the gate has no effect, and the gate only plays a triggering role. .

As shown in the figure below, when a negative voltage is applied to the gate G, the thyristor will not conduct, so the light bulb will not light!

As shown in the figure below, when reverse voltage is applied to the anode and cathode, the thyristor will not conduct, and the bulb will not light!

If the thyristor is turned on, the thyristor can only be turned off when the voltage (or current) of the main circuit is reduced to close to zero. As shown in the figure above, the thyristor can be turned off only by disconnecting S1.

Summary of conduction characteristics of unidirectional thyristor:

1. When the thyristor is subjected to the reverse anode voltage, no matter what voltage the gate is subjected to, the thyristor is in a reverse blocking state.

2. When the thyristor is subjected to the forward anode voltage, the thyristor is turned on only when the gate is subjected to the forward voltage.

3. When the thyristor is turned on, as long as there is a certain forward anode voltage, no matter what the gate voltage is, the thyristor remains on, that is, after the thyristor is turned on, the gate loses its function.

4. When the thyristor is turned on, when the main circuit voltage (or current) is reduced to close to zero, the thyristor is turned off.

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