What is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes 4 levels of semiconductor materials, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles are the critical parts of 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 popular in different electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the Thyristor is normally represented from 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-weight-controlled thyristors. The working condition of the thyristor is the fact when 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 utilized involving the anode and cathode (the anode is connected to the favorable pole of the power supply, as well as the cathode is connected to the negative pole of the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), as well as the indicator light fails to illuminate. This shows that the thyristor is not conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, and a forward voltage is used to the control electrode (referred to as a trigger, as well as the applied voltage is referred to as trigger voltage), the indicator light switches 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 when the voltage in the control electrode is taken away (that is certainly, K is switched on again), the indicator light still glows. This shows that the thyristor can continue to conduct. At this time, in order to 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 used to the control electrode, a reverse voltage is used involving the anode and cathode, as well as the indicator light fails to illuminate currently. This shows that the thyristor is not conducting and will reverse blocking.

5. In conclusion

1) When 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) When the thyristor is put through a forward anode voltage, the thyristor will simply conduct once the gate is put through a forward voltage. At this time, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) When the thyristor is switched on, so long as there is a specific forward anode voltage, the thyristor will stay switched on regardless of the gate voltage. That is certainly, following the thyristor is switched on, the gate will lose its function. The gate only functions 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 problem for the thyristor to conduct is the fact a forward voltage ought to be applied involving the anode as well as the cathode, and an appropriate forward voltage ought 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 must be stop, or the voltage must be reversed.

Working principle of thyristor

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

1. If a forward voltage is used 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 is still turned off because BG1 has no base current. If a forward voltage is used to the control electrode currently, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in the collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current is going to be introduced the collector of BG2. This current is delivered to BG1 for amplification and after that 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 big current appears in the emitters of these two transistors, that is certainly, the anode and cathode of the thyristor (how big the current is actually based on how big the stress and how big Ea), therefore the thyristor is totally switched on. This conduction process is done in a very short period of time.
2. Following the thyristor is switched on, its conductive state is going to be maintained from the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it really is still in the conductive state. Therefore, the purpose of the control electrode is only to trigger the thyristor to change on. When the thyristor is switched on, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor would be to decrease the anode current that it is insufficient to keep the positive feedback process. The best way to decrease the anode current would be to stop the forward power supply Ea or reverse the bond of Ea. The minimum anode current required to maintain 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 lower than the holding current, the thyristor can be turned off.

What exactly is the distinction between a transistor and 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 work of the transistor relies on electrical signals to control its opening and closing, allowing fast switching operations.

The thyristor demands a forward voltage and a trigger current in the gate to change on or off.

Application areas

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

Thyristors are mainly utilized in electronic circuits like controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Means 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 managing the trigger voltage of the control electrode to understand the switching function.

Circuit parameters

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

To summarize, although transistors and thyristors may be used in similar applications sometimes, because of the different structures and working principles, they have noticeable differences in performance and make use of occasions.

Application scope of thyristor

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

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent 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 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. If you are looking for high-quality thyristor, please feel free to contact us and send an inquiry.