What is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure consists of 4 quantities of semiconductor elements, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three 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 working status. Therefore, thyristors are commonly used in various electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the Thyristor is normally represented by 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-controlled thyristors. The working condition in the thyristor is that when 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 between the anode and cathode (the anode is attached to the favorable pole in the power supply, as well as 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), as well as 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, along with a forward voltage is applied to the control electrode (referred to as a trigger, as well as the applied voltage is referred to as trigger voltage), the indicator light turns on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, right after the thyristor is excited, even when the voltage in the control electrode is taken away (that is certainly, K is excited again), the indicator light still glows. This demonstrates that the thyristor can carry on and conduct. Currently, so that you can stop the conductive thyristor, the power supply Ea must be stop 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 between the anode and cathode, as well as the indicator light will not light up at this time. This demonstrates that the thyristor is not really conducting and will reverse blocking.

5. In conclusion

1) When the thyristor is put through a reverse anode voltage, the thyristor is within a reverse blocking state whatever voltage the gate is put through.

2) When the thyristor is put through a forward anode voltage, the thyristor will simply conduct once the gate is put through a forward voltage. Currently, the thyristor is in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) When the thyristor is excited, so long as you will find a specific forward anode voltage, the thyristor will remain excited whatever the gate voltage. Which is, right after the thyristor is excited, the gate will lose its function. The gate only serves as a trigger.

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

5) The disorder for the thyristor to conduct is that a forward voltage ought to be applied between the anode as well as the cathode, plus an appropriate forward voltage should also be applied between the gate as well as the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode must be stop, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is essentially an exclusive triode made from three PN junctions. It can be equivalently thought to be consisting of a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If a forward voltage is applied between 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 is still 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 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 will be brought in the collector of BG2. This current is delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A large current appears inside the emitters of the two transistors, that is certainly, the anode and cathode in the thyristor (the size of the current is in fact determined by the size of the load and the size of Ea), and so the thyristor is totally excited. This conduction process is completed in a really short period of time.
2. Right after the thyristor is excited, its conductive state will be maintained by the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it 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 excited, the control electrode loses its function.
3. The best way to turn off the turned-on thyristor is to decrease the anode current that it is inadequate to maintain the positive feedback process. The best way to decrease the anode current is to stop 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, strictly speaking, so long as the anode current is lower than the holding current, the thyristor could be turned off.

What is the difference between a transistor along with a thyristor?

Structure

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

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

Working conditions:

The work of the transistor relies on electrical signals to control its closing and opening, 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 commonly used in amplification, switches, oscillators, along with other aspects of electronic circuits.

Thyristors are mostly utilized in electronic circuits like 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 achieve current amplification.

The thyristor is excited or off by manipulating the trigger voltage in the control electrode to understand the switching function.

Circuit parameters

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

To sum up, although transistors and thyristors can be used in similar applications sometimes, because of their different structures and working principles, they have got noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Inside the lighting field, thyristors can be used in dimmers and light 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 used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is actually one in the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the development of power industry, intelligent operation and maintenance handling of power plants, solar power panel 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.