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How To Test A Thyristor: A Step-By-Step Guide

How to test a thyristor?

In this article, we will provide a step-by-step guide on how to test a thyristor. We will cover the basic principles of thyristors, the tools and equipment required for testing, and the various tests that need to be performed to determine whether a thyristor is functioning correctly. By following our guide, you can ensure that your electronic equipment remains in good condition and is operating at optimal levels.


Thyristors are crucial components in a wide range of electronic devices and circuits, including motor drives, power supplies, and lighting control systems. However, these devices can fail over time due to various factors, such as overheating or incorrect usage. Testing thyristors is essential to ensure their proper functioning and avoid costly equipment failure.


It is essential to regularly test thyristors, particularly in high-stress environments where they are subjected to extreme temperatures or voltage levels. Testing thyristors can help prevent potential accidents or equipment failures, which can result in costly downtime and repairs. By understanding how to test thyristors and regularly checking your equipment, you can maintain your devices’ reliability and extend their lifespan.

how to test thyristors

Understanding The Thyristor

Thyristors are electronic devices used for power control and switching applications. They are also known as silicon-controlled rectifiers (SCRs), as they operate as a switch, allowing or blocking the flow of electrical current in a circuit. Thyristors are commonly used in devices such as motor drives, lighting control systems, and power supplies.


What Is A Thyristor?

A thyristor is a type of semiconductor device that acts as a switch for controlling electrical power. It is a four-layered device with three terminals: anode, cathode, and gate. The anode is the positive terminal, while the cathode is the negative terminal. The gate is the control terminal that controls the flow of current between the anode and cathode. The device has a unique ability to stay on even when the gate signal is removed. This feature makes it an ideal choice for high-power applications.


Thyristors are used in various applications, including AC motor control, DC power supplies, and lighting control. They are also used in electronic circuits that require a constant or variable amount of power to be controlled. The use of thyristors enables efficient and reliable control of electrical power, allowing for a more efficient use of energy and a reduction in waste.


One of the primary advantages of thyristors is their high power handling capability. They are capable of handling high voltage and current levels, making them ideal for use in high-power applications. Thyristors can also switch quickly, allowing for precise control of electrical power. This ability to switch quickly makes thyristors ideal for use in applications such as motor control, where fast and accurate switching is essential.

How Does A Thyristor Work?

A thyristor works by using a process known as latching, which involves triggering the device to conduct current between the anode and cathode terminals. The triggering process involves applying a small current to the gate terminal, which causes the thyristor to turn on and remain conducting even if the gate voltage is removed.


Once triggered, the thyristor remains conducting until the anode-cathode voltage drops below a certain level, known as the holding voltage. This means that the thyristor can act as a switch, allowing or blocking the flow of current in a circuit.


The latching process of a thyristor is due to the interaction between the P-N junctions that make up the device. When a current is applied to the gate terminal, it causes the P-N junctions to become forward-biased, allowing current to flow between the anode and cathode. Once the thyristor is conducting, it acts like a low-resistance conductor, allowing the current to flow with minimal resistance.


The thyristor can be turned off by reducing the current flowing through it to zero, which can be achieved by reducing the voltage across the device to below the holding voltage. Alternatively, the thyristor can be turned off by applying a reverse bias voltage to the device, causing it to stop conducting.

Types Of Thyristors

Thyristors come in various types, each with its unique characteristics and applications. Understanding the different types of thyristors is essential for selecting the appropriate device for a specific application.


Silicon-controlled rectifiers (SCRs): SCRs are the most commonly used type of thyristors. They are used in high power applications, such as motor drives, power supplies, and lighting control systems. SCRs have a high voltage and current rating, making them suitable for use in high-power circuits. They are unidirectional devices, allowing current to flow in only one direction.


Gate turn-off thyristors (GTOs): GTOs can be turned on and off quickly by applying a negative voltage to the gate terminal. They are commonly used in high-frequency circuits, such as inverters and power supplies. Unlike SCRs, GTOs are bidirectional, meaning they allow current to flow in both directions.


Thyristor-diode modules: Thyristor-diode modules combine a thyristor and diode in a single package. They are used in circuits that require both rectification and switching functions. Thyristor-diode modules are commonly used in motor control applications, power inverters, and industrial automation.


Reverse conducting thyristors (RCTs): RCTs are thyristors that can conduct current in both directions. They are commonly used in circuits that require bidirectional power flow, such as inverters and motor control applications. RCTs are highly efficient and can handle high power ratings.

Tools And Equipment Required

To test a thyristor, you will need a few tools and equipment. These include:


  1. Multimeter: A multimeter is an essential tool that is used to measure voltage, current, and resistance. It is used to test the thyristor’s voltage drop and resistance.

  2. Power source: A power source is required to apply a voltage to the thyristor. It is essential to use the correct voltage, as too high or too low voltage can damage the thyristor.

  3. Test cables: You will need test cables to connect the thyristor to the multimeter and the power source. Make sure the test cables are in good condition, and the connectors fit snugly into the test points.

  4. Wiring diagram: A wiring diagram is a graphical representation of the thyristor circuit, showing how the components are connected. The wiring diagram is essential to identify the thyristor’s terminals and ensure that it is connected correctly.

  5. Heat sink: A heat sink is a device that helps dissipate heat generated by the thyristor during operation. It is essential to use a heat sink when testing the thyristor to prevent it from overheating and getting damaged.

  6. Safety equipment: Always use appropriate safety equipment when testing thyristors, including gloves, safety glasses, and a grounded mat.

Testing a thyristor can be dangerous

So it is crucial to take the necessary precautions and use the right tools and equipment to avoid accidents.


When selecting a multimeter, it is essential to choose one that can measure the resistance and voltage levels of the thyristor accurately. You may also need to adjust the multimeter settings to get accurate readings. Ensure that the power source voltage matches the thyristor’s voltage rating to avoid damaging it.


Test cables are available in different lengths and connector types, so make sure you select the right ones for your application. Using the wrong test cables can result in incorrect readings, and this can lead to wrong conclusions about the thyristor’s condition.


When selecting a heat sink, choose one that can dissipate heat efficiently and can handle the thyristor’s power rating. The heat sink should also be in good condition to ensure proper heat dissipation.


Finally, always ensure that you have safety equipment and are working in a safe environment. The safety equipment will protect you from electric shock and other hazards associated with testing thyristors. Use a grounded mat to prevent electrostatic discharge and minimize the risk of accidental damage to the thyristor or other components.

test a thyristor with a DMM step by step guide

Testing the Thyristor

Testing a thyristor involves several steps to ensure that it is functioning correctly. In this section, we will provide a detailed explanation of each step involved in testing a thyristor.

Step 1: Checking for continuity

The first step in testing a thyristor is to check for continuity. Continuity is the unbroken flow of current between two points in a circuit. To test for continuity, use a multimeter to check for resistance between the anode and cathode terminals of the thyristor. If the multimeter reading shows a low resistance value, then the thyristor is conducting and has continuity. If the reading is high or infinite, then the thyristor is not conducting and has no continuity.

Step 2: Testing the PN junction

The next step is to test the PN junction of the thyristor. A thyristor has two PN junctions: the anode-cathode junction and the gate-cathode junction. To test the PN junction, use the multimeter’s diode test function. Connect the positive probe to the anode and the negative probe to the cathode. The multimeter should display a forward voltage drop across the junction, typically around 0.7 volts. Next, connect the positive probe to the gate and the negative probe to the cathode. The multimeter should display a forward voltage drop across this junction as well.

Step 3: Testing the trigger

The third step is to test the trigger of the thyristor. The trigger is the voltage required to turn on the thyristor. To test the trigger, connect the thyristor to a power source and use a voltage meter to measure the voltage at the gate. Slowly increase the voltage until the thyristor switches on. The voltage at which the thyristor switches on is the trigger voltage.

Step 4: Testing the breakdown voltage

The fourth step is to test the thyristor’s breakdown voltage. The breakdown voltage is the maximum voltage that the thyristor can withstand before it breaks down and conducts current. To test the breakdown voltage, gradually increase the voltage applied to the thyristor until it breaks down and conducts current. The voltage at which the thyristor conducts current is the breakdown voltage.

Step 5: Testing the switching performance

The final step is to test the thyristor’s switching performance. The switching performance refers to the speed at which the thyristor can turn on and off. To test the switching performance, apply a series of pulses to the gate and measure the thyristor’s response time. The response time is the time it takes for the thyristor to switch on and off in response to the gate pulses.


Testing a thyristor may seem daunting at first, but with the right tools and knowledge, it is an easy task to accomplish. By following the steps in this guide, you can be sure that your thyristor is in good working condition. Don’t hesitate to repeat these tests regularly to ensure that your equipment is always in good condition.

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