Silicon Controlled Switch (SCS) | Construction | Working | New Topic [2023]

In this note, we are talking about Silicon Controlled Switch or SCS, also Construction of SCS and Working Principle of SCS. Welcome to Poly Notes Hub, a leading destination for Diploma Engineering Notes.

Author Name: Arun Paul.

What is Silicon Controlled Switch or SCS?

The Silicon Controlled Switch, commonly known as the thyristor, is a semiconductor device that enables the flow of electric current under specific conditions. Unlike regular transistors, it once turned on, remains conductive until the current flowing through it drops to zero or until external control is applied to turn it off. Its unique switching capability makes it an essential component in various applications.

This device operates by providing a short current or voltage pulse to the gate terminal, which causes the device to conduct. Once activated, it is continues to conduct current from the anode to the cathode until the current through it falls below a certain threshold or the voltage across it reverses. This behavior enables it to act as a solid-state switch, controlling the flow of electricity in a circuit.

Construction of SCS

It consists of several layers of semiconductor material, primarily made of silicon. Its construction involves three terminals: Anode, Cathode, Anode gate and Cathode gate.

Below we discuss about each terminal of this thyristor –

• Anode (A): The anode is a major terminal of the SCS. It is usually connected to the positive side of the power supply or load in a circuit. Electrons enter the gadget through the anode terminal.
• Cathode (K): The cathode is the other major terminal of the SCS. It is usually connected to the negative side of the power supply or load in a circuit. Electrons exit the gadget through the cathode terminal.
• Anode Gate (G1): In certain SCS designs, the anode gate serves as an extra terminal. It controls the device’s switching behavior. By supplying a tiny positive voltage to the anode gate in relation to the cathode, the SCS can be activated, allowing current to flow from the anode to the cathode.
• Cathode Gate (G2): The cathode gate, like the anode gate, is an extra terminal in some SCS systems. It is used to activate and control the device. By introducing a tiny positive voltage to the cathode gate about the anode, the SCS can be induced to conduct, allowing current to flow from the anode to the cathode.

Working Principle of SCS

The operation of this thyristor relies on a phenomenon called “latch-up.” In its “off” state, it prevents the flow of current between the anode and cathode. When a positive voltage is applied between these terminals, the device remains in its “off” state until a gate pulse is applied. The gate pulse triggers the latch-up process, causing it to turn on and allowing current to flow from the anode to the cathode. Once triggered, this thyristor remains in the “on” state until the current flowing through it drops to zero or until external control is applied to turn it off.

Advantages

It has some advantages like –

1. It has High Efficiency.
2. It is Robustness, Reliability and Long life span.
3. This thyristor is Cost-Effectiveness.
4. High Power handling capability.
5. It has fast switching speed.

Disadvantages

It has some major drawbacks –

1. It can generate significant heat during operation.
2. It has limited ability to turn off once triggered into conduction.
3. It can be sensitive to voltage transients and overvoltage conditions.
4. These devices have a non-zero reverse recovery time.
5. These devices may be larger and heavier compared to some other semiconductor devices.

Applications

These are used in different places like –

1. Power Control Systems,
2. Lighting Control,
3. Converters and Inverters,
4. Pulse Generator,
5. Motor Control Systems,
6. AC and DC power supplies,
7. Welding Equipments,
8. Power Transmission and Distribution System,
9. Pulse Power Systems,
10. HVAC Systems etc.