Thyristors

The thyristors are used extensively in power electronic circuits. They are operated as bistable switches, operating from of state to conducting state. The member of the Thyristors family are SCR, LASCR, RCT, GTO, SITH, and MCT.

Applications of Thyristors

• Thyristors are used in speed controls
• Thyristors are used in light dimmers
• Thyristors are used in Rectifiers
• Thyristors are used in power supplies
• Thyristors are used in Inverters
• Thyristors are used in Battery charges
• Thyristors are used in camera flashes
• Thyristors are used in various types of circuits, such as logic and timer circuits.

V-I Characteristics of Thyristor

The V-I characteristics of thyristor is a graph between the anode current IA and the anode-cathode voltage VA for different values of gate current IG. This characteristics can be drawn by considering the basic operation of the SCR. The below figure shows the V-I characteristics which is also called as static-cathode characteristics. It basically consist of three regions, They are:

• Region 1
• Region 2
• Region 3

Region 1

When the positive terminal of the supply is connected to cathode and the negative terminal is connected to anode with gate circuit open then thyristor operates in region 1. In this region junction J1 and J3 becomes reverse biased, whereas the junction J2 becomes forward biased. The reverse biased junctions (J1 and J3) acts as open circuit and the forward biased junction(J2) acts as a short circuit, as shown in figure.

Region 2

When the positive terminal of the supply is connected to anode and the negative terminal is connected to cathode with gate circuit open then thyristor operates in region 2. In this region junction J1 and J3 becomes forward biased, whereas the junction J2 gets reverse biased. The forward biased junctions (J1 and J3) acts as short circuit and the reverse biased junction(J2) acts as a open circuit, as shown in figure. Even in this region, the thyristor does not conduct any current expect a very small value of the leakage current. This mode of thyristor is called as forward blocking mode. Just as the region 1, i. e., reverse blocking mode, the thyristor can be made to conduct in the forward blocking mode by increasing the anode-cathode voltage to a value called as forward breakdown voltage(VBO). Even this method is not recommended as it may also damage the thyristor. Hence, the thyristor does not conduct even in this mode and is treated as open switch.

Region 3

When the positive terminal of the supply is connected to anode and the negative terminal to cathode with gate circuit closed the operates in region 3. In this region, all the three junctions (J1, J2 and J3) act as short circuit shown in figure and hence conducts current. In this region thyristor is said to be in a forward conduction mode and hence acts as a closed switch. This method of conducting the thyristor is the most efficient, as it requires a voltage which is very much less than VBO. The only extra thing we require is a gate signal for a small period of latching current. Once the anode current attains this value, the gate losses the control and hence can be removed. The removal of the gate signal will not have any effect on the thyristor conduction. However, if the anode current decreases to a value called ad holding current, the thyristor will once again go back to the forward blocking gate. Hence, care must be taken that, the anode current should not drop below the holding current after the gate signal is removed.

In electronic components, Power Semiconductor Devices are electronic devices that need an external power source to operate actively. Materials used to make semiconductor devices are neither excellent insulators nor conductors. They mainly manipulate, amplify, switch, or control the flow of electric current or voltage in a circuit. Power Semiconductor Devices, like diodes, transistors, thyristors, and sensors require power to do their job. A circuit is an interconnection of components. These components are capable of performing active functions like amplification, rectification, and switching they are called Power Semiconductor Devices.

In this article, we will be going through Semiconductor Devices Which are mainly divided into Diodes, Thyristors and Transistors. Semiconductor Devices are Classified into Two-Terminals, Three-Terminals and Four-Terminals Devices, We will go in-depth about these Devices. We will go through working of diodes, Thyristors, Transistors and Look at Its vi characteristics, At last we will conclude our Article with Advantages, Disadvantages, Applications, and Some FAQs.