Just what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains four levels of semiconductor elements, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles would be 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 operating status. Therefore, thyristors are popular in a variety of electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a silicon-controlled rectifier is normally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The operating condition of the thyristor is that when a forward voltage is used, 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 attached 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 used to the control pole (i.e., K is disconnected), as well as the indicator light does not glow. This implies 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, as well as a forward voltage is used to the control electrode (called a trigger, as well as the applied voltage is known 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, whether or not the voltage around the control electrode is taken off (which is, K is switched on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At the moment, so that you can 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 does not glow currently. This implies that the thyristor is not really conducting and may reverse blocking.

5. To sum up

1) If the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state no matter what voltage the gate is put through.

2) If the thyristor is put through a forward anode voltage, the thyristor is only going to conduct if the gate is put through a forward voltage. At the moment, 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 serves 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 that thyristor to conduct is that a forward voltage needs to be applied involving the anode as well as the cathode, and an appropriate forward voltage should also be applied involving the gate as well as the cathode. To transform 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 distinctive triode composed of three PN junctions. It can be equivalently thought to be composed of 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 create a base current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in the collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current will likely be brought in 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 inside the emitters of these two transistors, which is, the anode and cathode of the thyristor (how big the current is really dependant on how big the stress and how big Ea), so the thyristor is completely switched on. This conduction process is completed in a very short time.
2. Following the thyristor is switched on, its conductive state will likely be maintained by the positive feedback effect of the tube itself. Even when 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. After the thyristor is switched on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor would be to lessen the anode current so that it is not enough to maintain the positive feedback process. How you can 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 known as the holding current of the thyristor. Therefore, as it happens, as long as the anode current is under the holding current, the thyristor could be turned off.

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

Structure

Transistors usually consist of a PNP or NPN structure composed 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 a transistor relies upon electrical signals to control its opening and closing, allowing fast switching operations.

The thyristor needs 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, along with other facets of electronic circuits.

Thyristors are mostly used in electronic circuits such as 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 accomplish current amplification.

The thyristor is switched on or off by manipulating 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 can be used in similar applications sometimes, because of the different structures and operating principles, they may have noticeable differences in performance and use 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 light control devices.
• In induction cookers and electric water heaters, thyristors can be used to control the current flow to the heating element.
• In electric vehicles, transistors can 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 working in the development of power industry, intelligent operation and maintenance handling of power plants, solar power panel 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.