So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four quantities of semiconductor components, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles are definitely 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 a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the semiconductor device is usually represented by 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 lightweight-controlled thyristors. The working condition of the thyristor is the fact that whenever a forward voltage is applied, the gate should have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage is utilized in between the anode and cathode (the anode is attached 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 applied for the control pole (i.e., K is disconnected), as well as the indicator light fails to light up. This demonstrates that the thyristor is not conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, and a forward voltage is applied for the control electrode (known as a trigger, as well as 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, right after the thyristor is turned on, even if 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 carry on and conduct. At the moment, 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 for the control electrode, a reverse voltage is applied in between the anode and cathode, as well as the indicator light fails to light up currently. This demonstrates that the thyristor is not conducting and can reverse blocking.

5. In summary

1) When 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) When the thyristor is exposed to a forward anode voltage, the thyristor is only going to conduct once the gate is exposed to a forward voltage. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) When the thyristor is turned on, so long as there is a specific forward anode voltage, the thyristor will remain turned on regardless of the gate voltage. That is, right after the thyristor is turned on, the gate will lose its function. The gate only serves 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 your thyristor to conduct is the fact that a forward voltage should be applied in between the anode as well as the cathode, and an appropriate forward voltage also need to be applied in between the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage in between the anode and cathode must be stop, or perhaps the voltage must be reversed.

Working principle of thyristor

A thyristor is basically an exclusive triode composed of three PN junctions. It may be equivalently thought to be composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. In case a forward voltage is applied in between the anode and cathode of the thyristor without applying a forward voltage for the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains turned off because BG1 has no base current. In case a forward voltage is applied for the control electrode currently, BG1 is triggered to create basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in its 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 sent to BG1 for amplification and after that 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 inside the emitters of the two transistors, that is, the anode and cathode of the thyristor (the size of the current is actually based on the size of the stress and the size of Ea), so the thyristor is totally turned on. This conduction process is completed in a really short time.
2. Following the thyristor is turned on, its conductive state is going to be maintained by the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it is still inside the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to change on. Once the thyristor is turned on, the control electrode loses its function.
3. The only method to turn off the turned-on thyristor would be to lessen the anode current so that it is inadequate to keep the positive feedback process. The best way to lessen the anode current would be to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep the thyristor inside the conducting state is called the holding current of the thyristor. Therefore, as it happens, so long as the anode current is lower than the holding current, the thyristor may be turned off.

What is the difference between a transistor and a thyristor?

Structure

Transistors usually consist of a PNP or NPN structure composed of three semiconductor materials.

The thyristor consists 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 closing and opening, 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 widely used in amplification, switches, oscillators, along with other facets of electronic circuits.

Thyristors are mostly utilized 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 accomplish current amplification.

The thyristor is turned on or off by manipulating 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 summarize, although transistors and thyristors can be used in similar applications in some instances, because of their different structures and working principles, they may have noticeable variations in performance and utilize occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors can be used in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors can be used to control the current flow for the heating element.
• In electric vehicles, transistors can be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is one of the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the growth and development of power industry, intelligent operation and maintenance handling of power plants, solar power panel and related solar products manufacturing.

It accepts payment via Bank 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.