What is SCR(Silicon controlled rectifier)

 

SCR Operations and Applications.

Introduction

Silicon Controlled Rectifier (SCR) is an electronic component used in the control of power. It is also called Thyristor or Reverse-blocking Thyristor. The SCR is a three-terminal device that is used to control the power of electrical circuits by switching on and off. It has a wide range of applications, from dimmer switches to electric motors to power supplies. This blog will discuss the operation, characteristics, and applications of the SCR.

Operation of SCR

An SCR is a type of transistor that is used in AC power control. It works as a switch that can turn on and off the power flow to a load. The device is triggered by a small current, which can be applied to the gate of the SCR. When the gate is triggered, the SCR turns on, allowing the current to flow to the load. Once the current starts flowing, the SCR remains on until the current falls below a minimum level or the power is turned off.

The SCR has three terminals: the anode, cathode, and gate. The anode is the positive terminal, the cathode is the negative terminal, and the gate is the control terminal. The device works on the principle of the P-N-P-N structure, which is a combination of a P-type and an N-type semiconductor material. When a voltage is applied to the anode and cathode of the SCR, a small amount of current flows from the anode to the cathode. This small amount of current is called the leakage current.

When a positive voltage is applied to the gate of the SCR, it triggers the device, and the SCR turns on. The triggering voltage is usually between 0.7V and 1V. Once the SCR is triggered, the current starts flowing from the anode to the cathode, and the SCR remains on until the current falls below a minimum level. The minimum level of current is called the holding current.

The SCR has two modes of operation: forward blocking and forward conduction. In the forward blocking mode, the SCR does not conduct current, and the voltage across the device is equal to the voltage applied to the anode. In the forward conduction mode, the SCR conducts current, and the voltage across the device is small.

Characteristics of SCR

The SCR has several characteristics that make it a popular component in power control circuits. The most important characteristics of the SCR are its turn-on time, turn-off time, and holding current.

Turn-on Time

The turn-on time of the SCR is the time it takes for the device to switch from the blocking state to the conducting state. The turn-on time is affected by the voltage applied to the gate of the SCR, the load resistance, and the forward voltage drop across the device.

Turn-off Time

The turn-off time of the SCR is the time it takes for the device to switch from the conducting state to the blocking state. The turn-off time is affected by the reverse voltage applied to the device, the load resistance, and the forward voltage drop across the device.

Holding Current

The holding current of the SCR is the minimum current required to keep the device in the conducting state. If the current falls below the holding current, the device switches back to the blocking state.

Applications of SCR

SCRs are used in a wide range of applications, from power control to electronic circuits. Some of the common applications of SCR are:

Power Control

SCRs are used in power control circuits to control the power to loads. They are used in light dimmers, electric motor speed controllers, and power supplies.

In light dimmers, the SCR is used to control the power to a light bulb. The amount of power delivered to the bulb is controlled by the voltage applied to the gate of the SCR.