An **SCR** (Silicon Controlled Rectifier) is called a **thyristor** because it belongs to a family of semiconductor devices that have similar characteristics to the SCR.
The term **"thyristor"** is derived from two words:
1. **"Thyratron"** – a type of gas-filled tube used for switching, which works similarly to a controlled rectifier.
2. **"Transistor"** – a semiconductor device used for amplification and switching.
The **SCR** is a type of **thyristor**, and it has four layers of semiconductor material (PNPN) and three junctions. It behaves as a switch, which can either conduct or block current depending on the applied gate signal.
The name **thyristor** refers to this family of semiconductor devices that function like controlled rectifiers. The **SCR**, being one of the most common types of thyristors, is used in applications where switching is needed, such as in power control, motor control, and light dimming.
So, the term "thyristor" is used to describe devices like SCR that can be triggered into conduction by a small input and can control large amounts of current.