What is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four levels of semiconductor materials, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles would be the critical parts from 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 working status. Therefore, thyristors are popular in a variety of electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the semiconductor device is normally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The working condition from the thyristor is that each time 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 utilized in between the anode and cathode (the anode is connected to the favorable pole from the power supply, as well as the cathode is attached to the negative pole from the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), as well as the indicator light does not glow. This shows that the thyristor will not be 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 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, after the thyristor is switched on, even if the voltage in the control electrode is removed (that is, K is switched on again), the indicator light still glows. This shows that the thyristor can still conduct. At this time, in order 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 used towards the control electrode, a reverse voltage is used in between the anode and cathode, as well as the indicator light does not glow at the moment. This shows that the thyristor will not be conducting and may reverse blocking.

5. In conclusion

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

2) If the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct if the gate is subjected to a forward voltage. At this time, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is switched on, as long as there is a specific forward anode voltage, the thyristor will always be switched on whatever the gate voltage. Which is, after the thyristor is switched on, the gate will lose its function. The gate only serves as a trigger.

4) If 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 your thyristor to conduct is that a forward voltage needs to be applied in between the anode as well as the cathode, as well as an appropriate forward voltage ought to be applied in between the gate as well as the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode should be cut off, or even the voltage should be reversed.

Working principle of thyristor

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

1. In case a forward voltage is used in between the anode and cathode from the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still switched 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 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 is going to be introduced the collector of BG2. This current is sent to BG1 for amplification and after that 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 in the emitters of the two transistors, that is, the anode and cathode from the thyristor (the dimensions of the current is actually dependant on the dimensions of the stress and the dimensions of Ea), and so the thyristor is completely switched on. This conduction process is finished in an exceedingly short time.
2. Following the thyristor is switched on, its conductive state is going to be maintained through the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it really is still in the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to change on. When the thyristor is switched on, the control electrode loses its function.
3. The only way to turn off the turned-on thyristor is to reduce the anode current that it is inadequate to keep the positive feedback process. The best way to reduce the anode current is to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to maintain the thyristor in the conducting state is known as the holding current from the thyristor. Therefore, as it happens, as long as the anode current is less than the holding current, the thyristor may be switched off.

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

Structure

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

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

Operating conditions:

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

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

Application areas

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

Thyristors are mainly used in electronic circuits such as 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 switched on or off by managing the trigger voltage from the control electrode to understand the switching function.

Circuit parameters

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

To sum up, although transistors and thyristors may be used in similar applications in some instances, because of their different structures and working principles, they may 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.
• In the lighting field, thyristors may be used in dimmers and light-weight control devices.
• In induction cookers and electric water heaters, thyristors may 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 is actually one from the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the progression of power industry, intelligent operation and maintenance handling of power plants, solar power panel and related solar products manufacturing.

It accepts payment via Credit 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.