Thyristor and Types of Thyristors
What is a Thyristor?
A thyristor is a four-layer semiconductor device (PNPN) used as a high-power electronic switch in power electronics.
Main Terminals
- Anode
- Cathode
- Gate
Working Principle
- A small gate signal turns the thyristor ON.
- Once ON, it keeps conducting even if the gate signal is removed.
- It turns OFF only when the current falls below a certain value.
Applications
- Power control circuits
- Motor speed control
- Light dimmers
- Controlled rectifiers
Types of Thyristors
1. SCR (Silicon Controlled Rectifier)
- Most common thyristor
- Three terminals: anode, cathode, gate
- Turns ON using gate signal
2. TRIAC
- Bidirectional thyristor
- Conducts in both directions
- Used in AC power control
3. DIAC
- Bidirectional trigger device
- No gate terminal
- Used to trigger TRIAC
4. GTO (Gate Turn-Off Thyristor)
- Can be turned ON and OFF using the gate
- Used in high power switching
5. LASCR (Light Activated SCR)
- Triggered by light
- Used in high voltage systems
6. BCT (Bipolar Controlled Thyristor)
- Advanced thyristor device
- Combines features of transistor and thyristor
- Used in high-power converters
7. RCT (Reverse Conducting Thyristor)
- Has built-in reverse diode
- Allows current flow in reverse direction
- Used in inverter circuits
8. ETO (Emitter Turn-Off Thyristor)
- Improved version of GTO
- Provides faster switching
- Used in high-power electronics and motor drives
Summary Table
| Type | Full Form | Main Feature | Application |
|---|---|---|---|
| SCR | Silicon Controlled Rectifier | Most common thyristor | Power control |
| TRIAC | Triode for AC | Bidirectional conduction | AC dimmers |
| DIAC | Diode for AC | Trigger device | Triggering TRIAC |
| GTO | Gate Turn-Off Thyristor | Gate can turn OFF device | Industrial drives |
| LASCR | Light Activated SCR | Triggered by light | High voltage systems |
| BCT | Bipolar Controlled Thyristor | Thyristor + transistor control | Power converters |
| RCT | Reverse Conducting Thyristor | Built-in reverse diode | Inverters |
| ETO | Emitter Turn-Off Thyristor | Fast switching | Motor drives |