Just what is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of 4 levels of semiconductor components, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 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 working status. Therefore, thyristors are widely used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the Thyristor is normally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The working condition of the thyristor is 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 can be used in between the anode and cathode (the anode is connected to the favorable pole of the power supply, and also the cathode is attached to the negative pole of the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), and also the indicator light does not glow. 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, as well as a forward voltage is applied towards the control electrode (called a trigger, and also 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, whether or not the voltage on the control electrode is taken away (that is, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. At the moment, to be able to 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 applied towards the control electrode, a reverse voltage is applied in between the anode and cathode, and also the indicator light does not glow at the moment. This demonstrates that the thyristor is not really conducting and may reverse blocking.

5. In conclusion

1) If the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state regardless of what voltage the gate is put through.

2) If the thyristor is put through a forward anode voltage, the thyristor will simply conduct when the gate is put through a forward voltage. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is turned on, so long as there exists a specific forward anode voltage, the thyristor will remain turned on regardless of the gate voltage. Which is, right after the thyristor is turned 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 problem for your thyristor to conduct is that a forward voltage needs to be applied in between the anode and also the cathode, and an appropriate forward voltage also need to be applied in between the gate and also the cathode. To turn off a conducting thyristor, the forward voltage in between the anode and cathode has to be stop, or even the voltage has to be reversed.

Working principle of thyristor

A thyristor is basically an exclusive triode made from three PN junctions. It could be equivalently viewed as composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. When a forward voltage is applied 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 remains turned off because BG1 has no base current. When a forward voltage is applied towards the control electrode at the moment, BG1 is triggered to generate basics current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in their collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current is going to be brought in the collector of BG2. This current is delivered to BG1 for amplification and then delivered 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 sizable current appears within the emitters of the two transistors, that is, the anode and cathode of the thyristor (how big the current is in fact dependant on how big the stress and how big Ea), so the thyristor is completely turned on. This conduction process is finished in an exceedingly limited time.
2. Following the thyristor is turned on, its conductive state is going to be maintained through the positive feedback effect of the tube itself. Even if the forward voltage of the control electrode disappears, it is still within the conductive state. Therefore, the purpose of the control electrode is only to trigger the thyristor to transform on. When the thyristor is turned on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor would be to decrease the anode current so that it is not enough to maintain the positive feedback process. The best way to decrease the anode current would be to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep the thyristor within the conducting state is known as the holding current of the thyristor. Therefore, as it happens, so long as the anode current is under the holding current, the thyristor can be turned off.

What is the difference between a transistor as well as 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.

Functioning conditions:

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

The thyristor needs a forward voltage as well as a trigger current on the gate to transform on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, along with 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 achieve current amplification.

The thyristor is turned on or off by controlling the trigger voltage of the control electrode to comprehend the switching function.

Circuit parameters

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

To summarize, although transistors and thyristors may be used in similar applications in some instances, 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 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 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 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 growth and development of power industry, intelligent operation and maintenance management of 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.