What is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of 4 quantities of semiconductor elements, including three PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These three poles are the critical parts in 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 functioning status. Therefore, thyristors are widely used in various electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any Thyristor is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The functioning condition in the thyristor is the fact each time 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 involving the anode and cathode (the anode is linked to the favorable pole in the power supply, and the cathode is connected to the negative pole in the power supply). But no forward voltage is applied for the control pole (i.e., K is disconnected), and the indicator light will not light up. This shows that the thyristor is not conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is applied for the control electrode (referred to as a trigger, and the applied voltage is known as trigger voltage), the indicator light switches on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, even when the voltage around the control electrode is taken away (that is, K is turned on again), the indicator light still glows. This shows that the thyristor can continue to conduct. At the moment, so that you can cut off the conductive thyristor, the power supply Ea must be cut off or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is applied for the control electrode, a reverse voltage is applied involving the anode and cathode, and the indicator light will not light up at the moment. This shows that the thyristor is not conducting and can reverse blocking.

5. To sum up

1) If the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state regardless of what voltage the gate is put through.

2) If the thyristor is put through a forward anode voltage, the thyristor is only going to conduct when the gate is put through a forward voltage. At the moment, the thyristor is in the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is turned on, as long as there exists a specific forward anode voltage, the thyristor will remain turned on whatever the gate voltage. That is, following the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

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

5) The problem for the thyristor to conduct is the fact a forward voltage ought to be applied involving the anode and the cathode, as well as an appropriate forward voltage should also be applied involving the gate and the cathode. To change off a conducting thyristor, the forward voltage involving the anode and cathode must be cut off, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is essentially a unique triode composed of three PN junctions. It may be equivalently thought to be composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is applied involving the anode and cathode in the thyristor without applying a forward voltage for 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 for the control electrode at the moment, BG1 is triggered to produce a base current Ig. BG1 amplifies this current, as well as 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 likely be brought in the collector of BG2. This current is delivered to BG1 for amplification and after that delivered to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A sizable current appears in the emitters of the two transistors, that is, the anode and cathode in the thyristor (how big the current is in fact based on how big the stress and how big Ea), and so the thyristor is entirely turned on. This conduction process is finished in an exceedingly short time.
2. After the thyristor is turned on, its conductive state will likely be maintained through the positive feedback effect in the tube itself. Whether or not the forward voltage in the control electrode disappears, it really is still in the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. After the thyristor is turned on, the control electrode loses its function.
3. The only way to switch off the turned-on thyristor is always to reduce the anode current that it is insufficient to keep the positive feedback process. The way to reduce the anode current is always to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to keep your thyristor in the conducting state is known as the holding current in the thyristor. Therefore, strictly speaking, as long as the anode current is under the holding current, the thyristor could be turned off.

Exactly what is the distinction between a transistor as well as a thyristor?

Structure

Transistors usually consist of a PNP or NPN structure composed of three semiconductor materials.

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

Functioning conditions:

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

The thyristor demands a forward voltage as well as a trigger current at the gate to change on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, and other aspects of electronic circuits.

Thyristors are mainly utilized in electronic circuits including controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Way of working

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

The thyristor is turned on or off by managing the trigger voltage in the control electrode to comprehend the switching function.

Circuit parameters

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

To sum up, although transistors and thyristors can be utilized in similar applications sometimes, because of the different structures and functioning principles, they have noticeable differences in performance and utilize occasions.

Application scope of thyristor

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

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is one in the leading enterprises in the Home Accessory & Solar Power System, which can be fully working in the development of power industry, intelligent operation and maintenance handling of power plants, solar power panel and related solar products manufacturing.

It accepts payment via Bank 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.