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 would be 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 working status. Therefore, thyristors are widely used in different electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a silicon-controlled rectifier is normally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The working condition of the thyristor is the fact that each time a forward voltage is used, 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 used in between the anode and cathode (the anode is linked to the favorable pole of the power supply, and also the cathode is connected to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light fails to light up. 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, as well as a forward voltage is used towards the control electrode (referred to as a trigger, and also 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, following the thyristor is switched on, even if the voltage on the control electrode is taken off (that is, K is switched on again), the indicator light still glows. This demonstrates that the thyristor can still conduct. At the moment, so that you can stop the conductive thyristor, the power supply Ea has to be stop 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, and also the indicator light fails to light up at this time. This demonstrates that the thyristor will not be conducting and will reverse blocking.

5. In summary

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is exposed to.

2) If the thyristor is exposed to a forward anode voltage, the thyristor will only conduct if the gate is exposed to a forward voltage. At the moment, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is switched on, so long as there is a specific forward anode voltage, the thyristor will always be switched on regardless of the gate voltage. That is, following the thyristor is switched on, the gate will lose its function. The gate only serves as a trigger.

4) If 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 your thyristor to conduct is the fact that a forward voltage needs to be applied in between the anode and also the cathode, and an appropriate forward voltage ought to be applied in between the gate and also the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode has to be stop, or perhaps the voltage has to be reversed.

Working principle of thyristor

A thyristor is essentially a unique triode composed of three PN junctions. It could be equivalently viewed as comprising a PNP transistor (BG2) and an NPN transistor (BG1).

1. If a forward voltage is used in between 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 switched off because BG1 has no base current. If a forward voltage is used towards the control electrode at this time, BG1 is triggered to generate basics current Ig. BG1 amplifies this current, as well as 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 a vital positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A large current appears in the emitters of these two transistors, that is, the anode and cathode of the thyristor (the size of the current is in fact based on the size of the stress and the size of Ea), and so the thyristor is totally switched on. This conduction process is done in a really short time.
2. Following 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 really is still in the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to turn on. Once the thyristor is switched on, the control electrode loses its function.
3. The only method to shut off the turned-on thyristor would be to decrease the anode current so that it is insufficient to maintain the positive feedback process. How you can decrease the anode current would be to stop the forward power supply Ea or reverse the bond of Ea. The minimum anode current necessary to keep the thyristor in the conducting state is referred to as the holding current of the thyristor. Therefore, as it happens, so long as the anode current is under the holding current, the thyristor could be switched off.

Exactly what is the distinction between a transistor as well as a thyristor?

Structure

Transistors usually include a PNP or NPN structure composed of 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 a transistor relies upon electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor demands a forward voltage as well as a trigger current in the gate to turn on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, and other elements of electronic circuits.

Thyristors are mainly used 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 attain current amplification.

The thyristor is switched on or off by controlling the trigger voltage of the control electrode to realize 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 utilized in similar applications in some cases, due to their different structures and working principles, they may 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 light control devices.
• In induction cookers and electric water heaters, thyristors can be used to control the current flow towards the heating element.
• In electric vehicles, transistors can be utilized in motor controllers.

Supplier

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