Just what is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of four levels of semiconductor components, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles are the critical parts of 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 various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any silicon-controlled rectifier is usually 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-weight-controlled thyristors. The operating condition of the thyristor is that when 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 attached to the favorable pole of the power supply, as well as the cathode is linked to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), as well as the indicator light fails to glow. This shows that the thyristor is not conducting and has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is used towards the control electrode (known as a trigger, as well as the applied voltage is referred to 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, following the thyristor is turned on, even if the voltage in the control electrode is removed (that is certainly, K is turned on again), the indicator light still glows. This shows that the thyristor can carry on and conduct. At this time, in order to 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 used towards the control electrode, a reverse voltage is used involving the anode and cathode, as well as the indicator light fails to glow at the moment. This shows that the thyristor is not conducting and will reverse blocking.

5. To sum up

1) Once the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state no matter what voltage the gate is put through.

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

3) Once the thyristor is turned on, so long as there exists a specific forward anode voltage, the thyristor will stay turned on whatever 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) Once the thyristor is on, as well as the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

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

Working principle of thyristor

A thyristor is essentially an exclusive triode made from three PN junctions. It could be equivalently viewed as comprising a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case 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 is still turned off because BG1 has no base current. In case a forward voltage is used towards the control electrode at the moment, BG1 is triggered to create basics current Ig. BG1 amplifies this current, along with a ß1Ig current is obtained in their collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current will 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 a vital positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A large current appears inside the emitters of these two transistors, that is certainly, the anode and cathode of the thyristor (the dimensions of the current is actually based on the dimensions of the burden and the dimensions of Ea), and so the thyristor is entirely turned on. This conduction process is finished in an exceedingly limited time.
2. Following the thyristor is turned on, its conductive state will be maintained through the positive feedback effect of the tube itself. Even if the forward voltage of the control electrode disappears, it is still inside the conductive state. Therefore, the purpose of the control electrode is only to trigger the thyristor to turn 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 so that it is insufficient to keep up the positive feedback process. The best way to decrease the anode current is always to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current required to keep the thyristor inside the conducting state is referred to as the holding current of the thyristor. Therefore, as it happens, so long as the anode current is less than the holding current, the thyristor can be turned off.

Exactly what is the distinction between a transistor along with a thyristor?

Structure

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

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

Working conditions:

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

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

Application areas

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

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

Method 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 of the control electrode to understand 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 may be used in similar applications sometimes, because of the different structures and operating principles, they have noticeable variations 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.
• Within the lighting field, thyristors may be used in dimmers and light-weight control devices.
• In induction cookers and electric water heaters, thyristors could 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 a superb thyristor supplier. It is actually one of the leading enterprises in the Home Accessory & Solar Power System, which can be fully working in the growth and development of power industry, intelligent operation and maintenance management of power plants, solar power and related solar products manufacturing.

It accepts payment via Charge 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.