Fundamentals of Electronics | Lecture - 9A | Thyristors Principles, Families, and Applications

A Thyristor is a four-layer semiconductor device that has four alternating layers of P-type and N-type material (PNPN). When a small current is applied to its gate, it triggers a large current to flow between the anode and cathode. Once the device is "on," it remains conducting even after the gate current is removed, until the current flowing through it is reduced to zero. Thyristors are latching devices, meaning they only turn off when the current drops below a certain threshold.

#### Thyristor Families

1. Silicon Controlled Rectifier (SCR): The most common type of thyristor, used primarily in power switching applications.
2. Triac: A bidirectional thyristor used in AC power control applications.
3. Diac: A bidirectional device used for triggering triacs.
4. Gate Turn-Off (GTO) Thyristor: Can be turned off by a gate signal, unlike regular thyristors.
5. Shockley Diode: A simple form of a thyristor with only two terminals and a lower holding current.
6. Light-Activated Thyristor (LASCR): A thyristor activated by light instead of a gate signal.
7. Static Induction Thyristor (SIT): A fast-switching thyristor designed for high-speed switching applications.

#### Applications

1. Power Control: Thyristors are widely used in controlling and switching high-voltage and high-current circuits, such as in motor drives, lighting control, and HVDC transmission.
2. Overvoltage Protection: Thyristors are used in surge protectors and crowbar circuits to safeguard sensitive equipment.
3. AC Voltage Regulation: In light dimmers, fan speed controls, and heating elements, thyristors provide efficient control of AC power.
4. Inverters and Converters: Used in DC-AC inverters, DC-DC converters, and power supplies.
5. Electronics: In pulse circuits, timing circuits, and logic circuits for signal switching.
6. Thyristor-controlled rectifiers (TCR) are used in AC/DC power supplies for industries needing precise power regulation.

Search Queries
1. What are the types of thyristors and their applications?
2. How does a thyristor work?
3. SCR vs Triac: Key differences
4. How to choose a thyristor for power control?
5. Thyristor switching circuits and designs
6. Gate turn-off thyristor (GTO) applications
7. Thyristor in AC power control
8. Advantages of using thyristors over transistors
9. How does a thyristor differ from a diode or transistor?
10. Thyristors in high-voltage power systems

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