What is a thyristor?

A thyristor is a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure includes 4 quantities of semiconductor elements, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three 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 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 a Thyristor is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The functioning condition of the thyristor is the fact whenever 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 in between the anode and cathode (the anode is attached to the favorable pole of the power supply, and also the cathode is linked to the negative pole of the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and also the indicator light fails to light up. 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 applied to the control electrode (referred to as a trigger, and also 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 switched on, even when the voltage around the control electrode is taken away (that is, K is switched on again), the indicator light still glows. This shows that the thyristor can still conduct. Currently, to be able to shut down the conductive thyristor, the power supply Ea should 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 in between the anode and cathode, and also the indicator light fails to light up at this time. This shows that the thyristor is not conducting and can reverse blocking.

5. To sum up

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

2) When the thyristor is subjected to a forward anode voltage, the thyristor will only conduct once the gate is subjected to a forward voltage. Currently, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) When the thyristor is switched on, as long as you will find a specific forward anode voltage, the thyristor will always be switched on no matter the gate voltage. That is certainly, following the thyristor is switched on, the gate will lose its function. The gate only functions as a trigger.

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

5) The disorder for the thyristor to conduct is the fact a forward voltage ought to be applied in between the anode and also the cathode, and an appropriate forward voltage should also be applied in between the gate and also the cathode. To transform off a conducting thyristor, the forward voltage in between the anode and cathode should be shut down, or the voltage should be reversed.

Working principle of thyristor

A thyristor is actually a distinctive triode made up of three PN junctions. It could be equivalently thought to be composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. If a forward voltage is applied in between the anode and cathode of the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains 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 produce 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 brought in the collector of BG2. This current is brought to BG1 for amplification and then brought 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 big current appears inside the emitters of these two transistors, that is, the anode and cathode of the thyristor (the dimensions of the current is actually based on the dimensions of the stress and the dimensions of Ea), so the thyristor is completely switched on. This conduction process is done in a really limited time.
2. After the thyristor is switched 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 function of the control electrode is only to trigger the thyristor to change on. After the thyristor is switched on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor is to decrease the anode current that it is inadequate to keep the positive feedback process. How you can decrease the anode current is to shut down the forward power supply Ea or reverse the link of Ea. The minimum anode current required to keep the thyristor inside the conducting state is called the holding current of the thyristor. Therefore, strictly speaking, as long as the anode current is lower than the holding current, the thyristor could be turned off.

What exactly is the difference between a transistor along with 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 a transistor depends on electrical signals to control its opening and closing, allowing fast switching operations.

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

Application areas

Transistors are widely used in amplification, switches, oscillators, along with 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.

Method of working

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

The thyristor is switched on or off by manipulating the trigger voltage of the control electrode to understand 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 sum up, although transistors and thyristors can be utilized in similar applications sometimes, because of their different structures and functioning principles, they have noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be utilized in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors can be utilized in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors may be used to control the current flow to 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 actually one of the leading enterprises in the Home Accessory & Solar Power System, which is fully working in the development of power industry, intelligent operation and maintenance management 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.