What is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains 4 quantities of semiconductor elements, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles would be the critical parts of the thyristor, letting it 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 popular in a variety of electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any silicon-controlled rectifier is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The functioning condition of the thyristor is the fact that whenever a forward voltage is used, the gate needs to have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage is used involving the anode and cathode (the anode is connected to the favorable pole of the power supply, and also the cathode is attached to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light does not light up. This demonstrates that the thyristor is not conducting and contains forward blocking capability.

2. Controllable conduction

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

3. Continuous conduction

As shown in Figure c above, right after the thyristor is turned on, even when the voltage around the control electrode is taken away (which is, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. At the moment, in order to shut down the conductive thyristor, the power supply Ea must be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used towards the control electrode, a reverse voltage is used involving the anode and cathode, and also the indicator light does not light up at this time. This demonstrates that the thyristor is not conducting and may reverse blocking.

5. In conclusion

1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is within a reverse blocking state regardless of what voltage the gate is subjected to.

2) Once the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct when the gate is subjected to a forward voltage. At the moment, the thyristor is incorporated in the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) Once the thyristor is turned on, so long as there is a specific forward anode voltage, the thyristor will always be turned on whatever the gate voltage. That is certainly, right after the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

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

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

Working principle of thyristor

A thyristor is actually an exclusive triode made up of three PN junctions. It may be equivalently viewed as comprising a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is used involving the anode and cathode of the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be switched off because BG1 has no base current. If a forward voltage is used towards the control electrode at this time, BG1 is triggered to create a base current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in its collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current will likely be introduced the collector of BG2. This current is delivered to BG1 for amplification and then delivered 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 sizable current appears inside the emitters of these two transistors, which is, the anode and cathode of the thyristor (how big the current is actually based on how big the burden and how big Ea), therefore the thyristor is entirely turned on. This conduction process is finished in a really short period of time.
2. After the thyristor is turned on, its conductive state will likely be maintained through the positive feedback effect of the tube itself. Even when the forward voltage of the control electrode disappears, it really is still inside 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 to lessen the anode current so that it is not enough to keep the positive feedback process. The best way to lessen the anode current is to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current needed to keep the thyristor inside the conducting state is known as the holding current of the thyristor. Therefore, as it happens, so long as the anode current is lower than the holding current, the thyristor can be switched off.

Exactly what is the difference between a transistor and a thyristor?

Structure

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

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

Functioning conditions:

The job of any transistor relies upon electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor requires a forward voltage and a trigger current in the gate to turn on or off.

Application areas

Transistors are popular in amplification, switches, oscillators, and other elements of electronic circuits.

Thyristors are mostly found 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 of the control electrode to realize the switching function.

Circuit parameters

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

To summarize, although transistors and thyristors may be used in similar applications in some cases, because of their different structures and functioning principles, they have noticeable differences in performance and make use of occasions.

Application scope of thyristor

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

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It really is one of the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the growth and development of power industry, intelligent operation and maintenance handling of power plants, solar power 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.