Just what is a thyristor?

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

The graphical symbol of a silicon-controlled rectifier is usually represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The functioning condition in the thyristor is the fact that each time 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 utilized involving the anode and cathode (the anode is connected to the favorable pole in the power supply, and also the cathode is connected to the negative pole in the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), and also the indicator light will not light up. This shows that the thyristor is not really conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is applied towards the control electrode (called 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 (which is, K is switched on again), the indicator light still glows. This shows that the thyristor can continue to conduct. At this time, so that you can 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 towards the control electrode, a reverse voltage is applied involving the anode and cathode, and also the indicator light will not light up currently. This shows that the thyristor is not really conducting and can reverse blocking.

5. In conclusion

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is within a reverse blocking state whatever voltage the gate is exposed to.

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

3) If the thyristor is switched on, as long as you will find a specific forward anode voltage, the thyristor will remain switched on whatever the gate voltage. Which is, following the thyristor is switched on, the gate will lose its function. The gate only functions 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 condition for the thyristor to conduct is the fact that a forward voltage should be applied involving the anode and also the cathode, and an appropriate forward voltage also need to be applied involving the gate and also the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode should be shut down, or perhaps the voltage should be reversed.

Working principle of thyristor

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

1. In case a forward voltage is applied involving the anode and cathode in the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be turned off because BG1 has no base current. In case a forward voltage is applied towards the control electrode currently, BG1 is triggered to create basics current Ig. BG1 amplifies this current, along with a ß1Ig current is obtained in their 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 get into a saturated conduction state quickly. A sizable current appears in the emitters of the two transistors, which is, the anode and cathode in the thyristor (the size of the current is actually determined by the size of the load and the size of Ea), so the thyristor is entirely switched on. This conduction process is finished in a really short time.
2. Following the thyristor is switched on, its conductive state will be maintained from the positive feedback effect in the tube itself. Whether or not the forward voltage in the control electrode disappears, it really is still in the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to turn on. Once 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 so that it is inadequate to maintain the positive feedback process. The way to reduce the anode current is to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current necessary to keep your thyristor in the conducting state is called the holding current in the thyristor. Therefore, as it happens, as long as the anode current is lower than the holding current, the thyristor could be turned off.

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

Structure

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

The thyristor consists 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 demands a forward voltage along with a trigger current at the gate to turn on or off.

Application areas

Transistors are popular in amplification, switches, oscillators, as well as other aspects of electronic circuits.

Thyristors are mainly found 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 achieve current amplification.

The thyristor is switched on or off by controlling the trigger voltage in the control electrode to realize the switching function.

Circuit parameters

The circuit parameters of thyristors are based on 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, due to their different structures and functioning principles, they have got noticeable variations in performance and utilize occasions.

Application scope of thyristor

• In power electronic equipment, thyristors may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors may be used in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors could 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 a superb thyristor supplier. It is one in the leading enterprises in the Home Accessory & Solar Power System, that is fully active in the progression of power industry, intelligent operation and maintenance control over power plants, solar power 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.