Just what is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes 4 quantities of semiconductor materials, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles are definitely 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 operating status. Therefore, thyristors are popular in a variety of electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any Thyristor 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 in the thyristor is the fact each time a forward voltage is applied, the gate should 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 linked to the favorable pole in the power supply, and also the cathode is attached to the negative pole in the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and also the indicator light will not light up. This demonstrates that the thyristor is not really conducting and contains forward blocking capability.

2. Controllable conduction

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

3. Continuous conduction

As shown in Figure c above, after the thyristor is turned on, even when the voltage on the control electrode is taken away (that is certainly, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can carry on and conduct. At the moment, to be able to cut off the conductive thyristor, the power supply Ea should be cut off 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 involving the anode and cathode, and also the indicator light will not light up at the moment. This demonstrates that the thyristor is not really conducting and will reverse blocking.

5. In summary

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

2) When the thyristor is exposed to a forward anode voltage, the thyristor is only going to conduct if the gate is exposed to a forward voltage. At the moment, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

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

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

5) The condition for your thyristor to conduct is the fact a forward voltage needs to be applied involving the anode and also the cathode, plus an appropriate forward voltage ought to be applied involving the gate and also the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode should be cut off, or even the voltage should be reversed.

Working principle of thyristor

A thyristor is essentially an exclusive triode composed of three PN junctions. It could be equivalently regarded as comprising a PNP transistor (BG2) plus an NPN transistor (BG1).

1. In case a forward voltage is applied involving the anode and cathode in the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be turned off because BG1 has no base current. In case a forward voltage is applied to the control electrode at the moment, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, and 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 sent to BG1 for amplification and then sent 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 large current appears inside the emitters of these two transistors, that is certainly, the anode and cathode in the thyristor (the size of the current is really based on the size of the load and the size of Ea), so the thyristor is totally turned on. This conduction process is finished in a really limited time.
2. After the thyristor is turned on, its conductive state will be maintained by the positive feedback effect in the tube itself. Even when the forward voltage in the control electrode disappears, it is actually still inside the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to change on. Once the thyristor is turned on, the control electrode loses its function.
3. The only method to turn off the turned-on thyristor is always to decrease the anode current that it is not enough to keep the positive feedback process. The best way to decrease 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 inside the conducting state is referred to as the holding current in the thyristor. Therefore, as it happens, as long as the anode current is less than the holding current, the thyristor could be turned off.

What is the difference between a transistor and a thyristor?

Structure

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

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

Operating conditions:

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

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

Application areas

Transistors are popular in amplification, switches, oscillators, as well as other elements 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 accomplish 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 related to stability and reliability and often have higher turn-off voltage and larger on-current.

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

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In 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 is one in the leading enterprises in the Home Accessory & Solar Power System, that is fully working in the development of power industry, intelligent operation and maintenance control over power plants, solar 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.