Thyristor vs. Transistor: Key Points to Distinguish the Two

What is a Thyristor?

A thyristor or a Silicon Controlled Rectifier (SCR) is a three-terminal device. They are gate (control terminal), cathode (negative terminal), and anode (positive terminal) terminals.

 In addition, it has four semiconductor layers and functions as a rectifier. It can also be a switch in electric circuits and power supplies in digital circuits. We also view it as a tightly coupled pair of transistors. 

(thyristors). 

What is a Transistor?

A transistor is a semiconductor device that switches or amplifies signals in electric circuits. It has three terminals (base, collector, and emitter) and three semiconductor layers comprising the P-type and N-type. Because of the layer types, we have a variety of transistors, e.g., NPN transistors and PNP transistors (Bipolar junction transistors). 

(transistors)

Key Differences Between Thyristor vs. Transistor 

• High voltage and current rating

A thyristor has a distinct design that enables its operation on higher current ratings and voltage ratings than transistors. 

• Power handling capacity 

Thyristors can withstand very high power since they carry current at high voltages. Because of that, using thyristors in high-power applications is preferable. 

Conversely, transistors function in low voltage and current. Therefore, they can’t handle high power and are suitable for low-power applications. 

• Layers of Semiconductor material 

A transistor has three semiconductor layers with N-type and P-type materials.

A thyristor has four layers whereby the N-type and P-type semiconductor material has an alternating connection (PNPN). 

Composition

Both the transistor and thyristor have unique designs with specific components. You can get a transistor by joining three semiconductor layers. Then, the thyristor has four semiconductor layers of N-type and P-type materials arranged alternatingly. 

Number of junctions 

Transistors have two junctions, whereas thyristors have three links. 

The overall cost of the system

Generally, transistors in electronic circuits reduce the cost of the system, while thyristors increase the system cost, therefore being expensive. 

Mode of operation

A thyristor involves a momentary gate pulse in latching a device in a conduction state. 

For a transistor’s mode of operation, you’ll apply a pulse at the base terminal to begin conduction. Afterward, you’ll have a steady base signal supply to maintain the conduction. 

Amplifier usage 

You can use transistors as amplifiers or switches, but a thyristor is only functional as a switch and not an amplifier. 

Internal Power Losses 

Both thyristors and transistors experience internal power losses. However, a thyristor experiences relatively lower losses than transistors, making them more efficient. 

Size of the circuit 

Circuits made from the two devices differ in size, and Thyristors are bulkier compared to smaller transistors. Thus, a transistor circuit design will generally be smaller and more compact than the thyristor design. 

Cost of the circuit

A circuit made from a thyristor is costly compared to the one made from a transistor, and it is because a thyristor is comparatively bulky. 

The requirement of the commutation circuit 

A thyristor needs a commutation circuit to help switch it off on command, whereas a transistor doesn’t require one. 

Turn-on and turn-off time

Transistors have a high switching speed, meaning you can quickly switch them on and off when need dictates. Hence, you can use them in high-frequency applications. 

Contrarily, thyristors have low switching speeds and can only be applicable in low-frequency applications. 

Suitability 

You’ll often apply transistors in high-frequency and low-power applications, whereas thyristors are best in low-frequency and high-power applications. 

(an electric motor with high-power application)

Forward current maintenance 

For a transistor circuit, you’ll need continuous input to maintain a forward current. 

Contrarily, you use a pulse in thyristors to keep the forward current flowing unless it falls below the threshold value. Also, you won’t need an input current. 

Triggering procedure

You must constantly provide a regular current pulse to a transistor to ensure effective conduction. 

A thyristor will only need one triggering pulse at the beginning to start and sustain conduction. 

Bulkiness 

A thyristor circuit is bulkier than a transistor circuit. 

Power rating 

Transistors have a low power rating (Watts), while thyristors can work under high power that goes up to KW (Kilowatts). 

Surge current capacity

A transistor circuit can endure a low rate of current change, and therefore, it doesn’t have a surge current capacity characteristic. 

A thyristor, however, can withstand a high rate of current change. Because of that, it exhibits a surge in current capacity characteristics. 

Conclusion

From our discussion above, we can now easily distinguish between a transistor and a thyristor. For example, a transistor is a three-layer device. But, a thyristor is a four-layer device, a significant difference between the two.

And so, each of them has a set of benefits depending on your needs. But, so far, we can see that thyristors have the upper hand on efficiency and reliability over transistors. 

All in all, we’ll be awaiting your inquiries or clarifications at any time. Just reach out to us and get your answers.