What is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four quantities of semiconductor elements, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles are definitely the critical parts from the thyristor, allowing it to control current and perform high-frequency switching operations. Thyristors can operate under high voltage and high current conditions, and external signals can maintain their operating status. Therefore, thyristors are commonly used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a semiconductor device is generally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The operating condition from the thyristor is that when a forward voltage is applied, the gate will need to have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage is utilized between the anode and cathode (the anode is attached to the favorable pole from the power supply, and the cathode is linked to the negative pole from the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and the indicator light will not light up. This implies that the thyristor is not conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is applied to the control electrode (known as a trigger, and the applied voltage is called trigger voltage), the indicator light turns on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, whether or not the voltage around the control electrode is taken away (that is, K is turned on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At this time, so that you can shut down the conductive thyristor, the power supply Ea has to be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is applied to the control electrode, a reverse voltage is applied between the anode and cathode, and the indicator light will not light up at this time. This implies that the thyristor is not conducting and may reverse blocking.

5. In summary

1) When the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state whatever voltage the gate is put through.

2) When the thyristor is put through a forward anode voltage, the thyristor will only conduct once the gate is put through a forward voltage. At this time, the thyristor is in the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) When the thyristor is turned on, so long as there exists a specific forward anode voltage, the thyristor will remain turned on regardless of the gate voltage. Which is, following the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

4) When the thyristor is on, and the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

5) The disorder for that thyristor to conduct is that a forward voltage ought to be applied between the anode and the cathode, as well as an appropriate forward voltage ought to be applied between the gate and the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode has to be shut down, or the voltage has to be reversed.

Working principle of thyristor

A thyristor is actually a unique triode made up of three PN junctions. It can be equivalently thought to be consisting of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is applied between the anode and cathode from the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still turned off because BG1 has no base current. If a forward voltage is applied to the control electrode at this time, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, along with a ß1Ig current is obtained in the collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current will be introduced the collector of BG2. This current is brought to BG1 for amplification and then brought to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A large current appears within the emitters of the two transistors, that is, the anode and cathode from the thyristor (the dimensions of the current is really determined by the dimensions of the burden and the dimensions of Ea), and so the thyristor is completely turned on. This conduction process is done in a very short time.
2. Right after the thyristor is turned on, its conductive state will be maintained by the positive feedback effect from the tube itself. Even if the forward voltage from the control electrode disappears, it is actually still within the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to turn on. When the thyristor is turned on, the control electrode loses its function.
3. The only way to turn off the turned-on thyristor is always to lessen the anode current that it is not enough to maintain the positive feedback process. How you can lessen the anode current is always to shut down the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep the thyristor within the conducting state is called the holding current from the thyristor. Therefore, as it happens, so long as the anode current is lower than the holding current, the thyristor can be turned off.

What is the difference between a transistor along with a thyristor?

Structure

Transistors usually contain a PNP or NPN structure made up of three semiconductor materials.

The thyristor consists of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.

Functioning conditions:

The task of a transistor depends on electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor demands a forward voltage along with a trigger current on the gate to turn on or off.

Application areas

Transistors are commonly used in amplification, switches, oscillators, along with other facets of electronic circuits.

Thyristors are mostly found in electronic circuits such as controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Means of working

The transistor controls the collector current by holding the base current to accomplish current amplification.

The thyristor is turned on or off by controlling the trigger voltage from the control electrode to realize the switching function.

Circuit parameters

The circuit parameters of thyristors are based on stability and reliability and usually have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors can be used in similar applications in some instances, due to their different structures and operating principles, they have noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors can be used in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors can be used to control the current flow to the heating element.
• In electric vehicles, transistors can be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a wonderful thyristor supplier. It really is one from the leading enterprises in the Home Accessory & Solar Power System, which is fully working in the development of power industry, intelligent operation and maintenance control over power plants, solar power and related solar products manufacturing.

It accepts payment via Credit Card, T/T, West Union and Paypal. PDDN will ship the goods to customers overseas through FedEx, DHL, by air, or by sea. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.