Thyristors fall into a diverse classification of semiconductor devices. They are similar to transistors, resistors, and diodes and are used to fulfil their shortcomings. If you want to use a thyristor in your electronic circuit, it is necessary to learn about the different types of thyristors and their functions. Let’s take a look!

What Is a Thyristor? 

Thyristor, also known as a silicon-controlled rectifier (SCR), is a 4-layered device having alternating N-type and P-type semiconductors (P-N-P-N).

A basic thyristor has 3 terminals – a control terminal (gate), a positive terminal (anode), and a negative terminal (cathode). The function of a thyristor is to operate as a switch, controlling electric power.

The thyristor is a lightweight and small component that guards electrical circuits with large currents and voltages (till 4500 A, 6000 V). As a thyristor can shift from conducting current to non-conducting current, it’s agreeable as a rectifier.

Even more, thyristors have maintenance costs if operated under the right conditions.

They have a wide range of usage in electric circuits – starting from burglar alarms to transformer lines.

Different Types of Thyristors and Their Functions 


Thyristors have different classes depending on their voltage, current, turn-on, and turn-off natures. These are:

  • Turn-on Capability

These types of thyristors give unidirectional control. One example will be a Light-activated silicon control rectifier (LASCR).

When light particles hit a reverse-biased junction, electron-hole pair numbers rise. The thyristor turns on when the light intensity goes above a critical value. It gives absolute electrical isolation between its power converter’s switching device and light source.

LASCRs can be seen in heavy-power pulse generators, HVDC transmission machines, and reactive power compensators.

  • Turn-Off Capability

Just like the turn-on thyristors, this type also offers unidirectional control. When enough gate pulse has been applied, the circuit’s main current needs to be interrupted to turn it off.

Gate turn-off thyristor (GTO) is an example that can be turned off by flowing negative current to the gate. It does not need the current between the cathode and anode to be removed.

To sum it up, the GTO can be switched off using a gate signal having a negative polarity, turning it into a controllable switch. The switch is called Gate-Controlled Switch.

GTOs are in use in AC and DC motor drives, AC stabilizing power, and heavy-powered inverters.

  • Bidirectional Control

The last type of thyristor falls under bidirectional control. These are connected in an anti-parallel manner, giving two different control circuits.

They can conduct current in two directions. An example of this is TRIAC (Triode for alternating current). On the halves of its alternating waveform, TRIACs offer control by delivering power efficiently.

Low-powered ones are used to control speed for electric motors and fans.

Final Words

That’s a wrap for now. Now, you know why it is essential to learn about different types of thyristors and their functions. Keep in mind that you need to choose the one that suits your electrical needs when you design the circuit.


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