So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes four levels 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, 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 functioning status. Therefore, thyristors are commonly used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a semiconductor device is generally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The functioning condition of the thyristor is the fact whenever a forward voltage is applied, 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 connected 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 applied to the control pole (i.e., K is disconnected), as well as the indicator light fails to illuminate. This demonstrates 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 applied to the control electrode (known as a trigger, as well as the applied voltage is known as trigger voltage), the indicator light switches on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, right after the thyristor is turned on, even if the voltage on the control electrode is taken away (which is, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can still conduct. At this time, so that you can cut off the conductive thyristor, the power supply Ea has to 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, as well as the indicator light fails to illuminate currently. This demonstrates that the thyristor will not be conducting and will reverse blocking.

5. In summary

1) When the thyristor is put through a reverse anode voltage, the thyristor is at 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 only conduct when the gate is put through a forward voltage. At this time, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, which is, the controllable characteristic.

3) When the thyristor is turned on, as long as you will find a specific forward anode voltage, the thyristor will remain turned on no matter the gate voltage. That is, right after the thyristor is turned on, 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 condition for that thyristor to conduct is the fact a forward voltage ought to be applied involving the anode as well as the cathode, as well as an appropriate forward voltage also need to be applied involving the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode has to be cut off, or the voltage has to be reversed.

Working principle of thyristor

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

1. If a forward voltage is applied involving 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 continues to be switched off because BG1 has no base current. If a forward voltage is applied to the control electrode currently, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, along with a ß1Ig current is obtained in its 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 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 in a saturated conduction state quickly. A sizable current appears inside the emitters of the two transistors, which is, the anode and cathode of the thyristor (how big the current is really determined by how big the load and how big Ea), so the thyristor is totally turned on. This conduction process is finished in a really limited time.
2. Following the thyristor is turned on, its conductive state will be maintained from the positive feedback effect of the tube itself. Even when the forward voltage of the control electrode disappears, it really is still inside the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to turn on. After the thyristor is turned on, the control electrode loses its function.
3. The best way to shut off the turned-on thyristor would be to lessen the anode current so that it is not enough to keep up the positive feedback process. The way to lessen the anode current would be to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep the thyristor inside the conducting state is known as the holding current of the thyristor. Therefore, strictly speaking, as long as the anode current is under the holding current, the thyristor can be switched off.

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

Structure

Transistors usually consist of 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.

Working conditions:

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

The thyristor requires 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, as well as other elements of electronic circuits.

Thyristors are mainly 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 attain current amplification.

The thyristor is turned 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 based on stability and reliability and often have higher turn-off voltage and larger on-current.

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

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors can be used in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors could 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 actually one of the leading enterprises in the Home Accessory & Solar Power System, which can be fully working in the progression of power industry, intelligent operation and maintenance handling of power plants, solar 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. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.