What is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor elements, including three PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These three poles are the critical parts in 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 commonly used in various electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a silicon-controlled rectifier is normally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The working condition in 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 can be used involving the anode and cathode (the anode is connected to the favorable pole in the power supply, and also the cathode is attached to the negative pole in the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and also the indicator light does not illuminate. This shows that the thyristor is not conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is used for the control electrode (referred to as a trigger, and also the applied voltage is known as trigger voltage), the indicator light switches 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, whether or not the voltage on the control electrode is taken off (that is, K is switched on again), the indicator light still glows. This shows that the thyristor can carry on and conduct. At this time, in order to shut down the conductive thyristor, the power supply Ea has to be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used for the control electrode, a reverse voltage is used involving the anode and cathode, and also the indicator light does not illuminate currently. This shows that the thyristor is not conducting and can reverse blocking.

5. To sum up

1) Once 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) Once the thyristor is exposed to a forward anode voltage, the thyristor will simply conduct when the gate is exposed to a forward voltage. At this time, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

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

4) Once the thyristor is on, and also 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 a forward voltage ought to be applied involving the anode and also the cathode, plus an appropriate forward voltage ought to be applied involving the gate and also the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode has to be shut down, or the voltage has to be reversed.

Working principle of thyristor

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

1. If a forward voltage is used involving the anode and cathode in 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. If a forward voltage is used for the control electrode currently, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, along with 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 delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A big current appears within the emitters of the two transistors, that is, the anode and cathode in the thyristor (the dimensions of the current is really determined by the dimensions of the stress and the dimensions of Ea), and so the thyristor is totally switched on. This conduction process is done in a very short time.
2. After the thyristor is switched on, its conductive state is going to be maintained from the positive feedback effect in the tube itself. Whether or not the forward voltage in the control electrode disappears, it is still within the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to transform on. When the thyristor is switched on, the control electrode loses its function.
3. The only way to turn off the turned-on thyristor would be to decrease the anode current so that it is insufficient to keep up the positive feedback process. How you can decrease the anode current would be to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to keep your thyristor within the conducting state is known as the holding current in the thyristor. Therefore, as it happens, so long as the anode current is less than the holding current, the thyristor could be turned off.

What is the difference between a transistor along with a thyristor?

Structure

Transistors usually include a PNP or NPN structure made from three semiconductor materials.

The thyristor is composed of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.

Working conditions:

The job of a transistor relies upon electrical signals to control its opening and closing, allowing fast switching operations.

The thyristor requires a forward voltage along with a trigger current in the gate to transform on or off.

Application areas

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

Thyristors are mostly used in electronic circuits including 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 switched on or off by controlling the trigger voltage in 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 can be utilized in similar applications sometimes, because of their different structures and working principles, they have noticeable variations in performance and make use of occasions.

Application scope of thyristor

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

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is actually one in the leading enterprises in the Home Accessory & Solar Power System, that is fully working 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.