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 levels of semiconductor materials, including three PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These three poles would be the critical parts in 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 operating status. Therefore, thyristors are widely used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a silicon-controlled rectifier is normally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The operating condition in the thyristor is the fact 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 used involving the anode and cathode (the anode is connected to the favorable pole in the power supply, and the cathode is attached to the negative pole in the power supply). But no forward voltage is applied for the control pole (i.e., K is disconnected), and the indicator light does not illuminate. This implies 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, and 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, after the thyristor is switched on, whether or not the voltage in the control electrode is taken away (that is certainly, K is switched on again), the indicator light still glows. This implies that the thyristor can continue to conduct. Currently, to be able to cut off the conductive thyristor, the power supply Ea has to be cut off 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 involving the anode and cathode, and the indicator light does not illuminate at this time. This implies that the thyristor is not conducting and may reverse blocking.

5. In conclusion

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is exposed to.

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

3) If the thyristor is switched on, as long as there exists a specific forward anode voltage, the thyristor will always be switched on no matter the gate voltage. That is, after the thyristor is switched on, the gate will lose its function. The gate only works as a trigger.

4) If the thyristor is on, and 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 should be applied involving the anode and the cathode, plus an appropriate forward voltage also need to be applied involving the gate and the cathode. To change off a conducting thyristor, the forward voltage involving the anode and cathode has to be cut off, or the voltage has to be reversed.

Working principle of thyristor

A thyristor is basically a distinctive triode composed of three PN junctions. It could be equivalently viewed as consisting of a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If a forward voltage is applied 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 switched off because BG1 has no base current. If a forward voltage is applied for the control electrode at this time, BG1 is triggered to create 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 will likely be brought in the collector of BG2. This current is sent to BG1 for amplification then sent to BG2 for amplification again. Such repeated amplification forms a crucial 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 certainly, the anode and cathode in the thyristor (how big the current is really determined by how big the stress and how big Ea), and so the thyristor is totally switched on. This conduction process is completed in an exceedingly limited time.
2. Following the thyristor is switched on, its conductive state will likely be maintained from the positive feedback effect in the tube itself. Whether or not the forward voltage in the control electrode disappears, it is actually still inside the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to transform on. When 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 that it is insufficient to keep the positive feedback process. The best way to reduce the anode current is always to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to keep the thyristor inside the conducting state is known as the holding current in the thyristor. Therefore, strictly speaking, as long as the anode current is less than the holding current, the thyristor may be switched off.

What is the distinction between a transistor and a thyristor?

Structure

Transistors usually contain 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.

Operating conditions:

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

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

Application areas

Transistors are widely used in amplification, switches, oscillators, as well as other aspects of electronic circuits.

Thyristors are mostly found in electronic circuits such as controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Method of working

The transistor controls the collector current by holding the base current to attain current amplification.

The thyristor is switched on or off by manipulating 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 operating principles, they may have noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be utilized in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors can be utilized in dimmers and light-weight control devices.
• In induction cookers and electric water heaters, thyristors may 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 one in the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the growth and development of power industry, intelligent operation and maintenance handling of power plants, solar 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.