Thyristors

Thyristors are four-layer semiconductor devices, also referred to as silicon-controlled rectifiers. It is a type of static switch that is very fast and made available to be used for automation and control purposes, such as the huge amount of voltage that is primarily used to control and automate the speed of DC Motors. 

How Does the Thyristor Function?

Thyristors have primarily three electrodes, such as an anode (positive terminal), a cathode (negative terminal), and a gate. A thyristor is also available with two or four leads. The main control terminal of this device is a gate when the main current transmits between the anode and cathode. They are typically composed of N-type and P-type materials. The N-type material is developed by doping an element with electrons to leverage the number of negative charge-carrying electrons.

Doping is also used to create P-type materials, although the resulting charge-carrying electrons are positively charged. A semiconductor thyristor device is created by layering P and N-type materials alternately. These devices are used to build a latching circuit. The gate can be used to activate it. When the voltage across the anode-cathode returns to zero, it Switches off.

Types of Thyristors

• Silicon-controlled rectifier (SCR) - The primary usage of an SCR is to work as a switch, which is typically used to turn on or off small or large amounts of voltage.
• Silicon Controlled Switch (SCS) - Silicon Controlled Switch, abbreviated SCS, is a piece of equipment exactly like an SCR. However, its designation is to turn on and off whenever a positive voltage/input voltage pulse is connected to an additional “Anode gate”.
• Triac - The triode for alternating current gave rise to the name triac. SCRs and triacs are similar, but triacs conduct in both directions (a bidirectional device). It can switch between AC and DC currents. This requires firing circuit commander modules.
• Four-layer diode - 2 pins are embedded typically in four-layer diodes and are similar to a voltage-sensitive switch. When the voltage passes through two pins, it breaks the voltage since it turns ON and OFF. 
• Diac - Diac is a combination of the terms "diode" and "ac switch," as it resembles a four-layer diode. However, it can be controlled in all directions in the sense that it makes the connection between AC and DC currents.

What are the Applications of Thyristors?

They are primarily used in several everyday applications, including:

• Light dimming devices
• Motor speed controls system
• Liquid level regulators
• Pressure control systems