Just what is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes four levels of semiconductor materials, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles would be 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 alteration.

The graphical symbol of the silicon-controlled rectifier is generally represented from 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 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 involving the anode and cathode (the anode is connected to the favorable pole of the power supply, as well as the cathode is attached 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 implies that the thyristor is not really 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 applied to the control electrode (called a trigger, as well as the applied voltage is called trigger voltage), the indicator light turns on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, right after the thyristor is switched on, even if the voltage around the control electrode is taken away (that is, K is switched on again), the indicator light still glows. This implies that the thyristor can continue to conduct. Currently, 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 applied to the control electrode, a reverse voltage is applied involving the anode and cathode, as well as the indicator light fails to illuminate at this time. This implies that the thyristor is not really conducting and will reverse blocking.

5. In conclusion

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

2) If the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct once the gate is subjected to a forward voltage. Currently, the thyristor is in the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is switched on, so long as there exists a specific forward anode voltage, the thyristor will stay switched on regardless of the gate voltage. That is, right after the thyristor is switched on, the gate will lose its function. The gate only functions as a trigger.

4) If the thyristor is on, as well as 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 ought to be applied involving the anode as well as the cathode, plus 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 actually a distinctive triode made up of three PN junctions. It may be equivalently viewed as composed of a PNP transistor (BG2) plus 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 is still switched off because BG1 has no base current. If a forward voltage is applied to the control electrode at this time, BG1 is triggered to create 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 will be introduced the collector of BG2. This current is sent to BG1 for amplification and then sent to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A big current appears within the emitters of these two transistors, that is, the anode and cathode of the thyristor (how big the current is actually based on how big the load and how big Ea), therefore the thyristor is completely switched on. This conduction process is done in a very limited time.
2. Right after the thyristor is switched on, its conductive state will be maintained from the positive feedback effect of the tube itself. Even if the forward voltage of the control electrode disappears, it is actually still within the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to change on. After the thyristor is switched on, the control electrode loses its function.
3. The best way to shut off the turned-on thyristor is always to reduce the anode current so that it is not enough to maintain the positive feedback process. The best way to reduce the anode current is always to stop the forward power supply Ea or reverse the connection of Ea. The minimum anode current required to keep your thyristor within the conducting state is called the holding current of the thyristor. Therefore, strictly speaking, so long as the anode current is lower than the holding current, the thyristor could be switched off.

What exactly is the distinction between a transistor as well as a thyristor?

Structure

Transistors usually contain a PNP or NPN structure made up of 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 depends on electrical signals to control its opening and closing, allowing fast switching operations.

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

Application areas

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

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

Way 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 in some cases, because of their different structures and working principles, they may 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.
• 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 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 actually one of the leading enterprises in the Home Accessory & Solar Power System, which can be fully working in the growth and development of power industry, intelligent operation and maintenance control over power plants, solar power 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.