So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure contains 4 levels of semiconductor elements, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles are 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 operating status. Therefore, thyristors are widely used in various electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the semiconductor device is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The operating condition of the thyristor is the fact whenever a forward voltage is applied, 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 is used in between the anode and cathode (the anode is linked to the favorable pole of the power supply, as well as the cathode is linked to the negative pole of the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), as well as the indicator light fails to illuminate. This demonstrates that the thyristor is not really conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is applied towards the control electrode (referred to as a trigger, as well as 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 excited, whether or not the voltage in the control electrode is taken away (that is certainly, K is excited again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. Currently, so that you can cut off the conductive thyristor, the power supply Ea must be cut off or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is applied towards the control electrode, a reverse voltage is applied in between the anode and cathode, as well as the indicator light fails to illuminate at this time. This demonstrates that the thyristor is not really conducting and may reverse blocking.

5. In summary

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is in 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 once the gate is exposed to a forward voltage. Currently, the thyristor is within the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) If the thyristor is excited, provided that you will find a specific forward anode voltage, the thyristor will always be excited no matter the gate voltage. Which is, after the thyristor is excited, the gate will lose its function. The gate only works as a trigger.

4) If the thyristor is on, as well as the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.

5) The disorder for that thyristor to conduct is the fact a forward voltage ought to be applied in between the anode as well as the cathode, as well as an appropriate forward voltage also need to be applied in between the gate as well as the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode must be cut off, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is actually an exclusive triode composed of three PN junctions. It may be equivalently regarded as consisting of a PNP transistor (BG2) as well as 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 towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be turned off because BG1 has no base current. In case a forward voltage is applied towards the control electrode at this time, BG1 is triggered to generate basics 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 after that sent to BG2 for amplification again. Such repeated amplification forms a vital 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 certainly, the anode and cathode of the thyristor (how big the current is really based on how big the stress and how big Ea), so the thyristor is completely excited. This conduction process is completed in an exceedingly limited time.
2. Following the thyristor is excited, its conductive state will likely be maintained through the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it is actually still within the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to transform on. When the thyristor is excited, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor is to reduce the anode current so that it is not enough to maintain the positive feedback process. The way to reduce the anode current is to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to maintain the thyristor within the conducting state is known as the holding current of the thyristor. Therefore, strictly speaking, provided that the anode current is lower than the holding current, the thyristor may be turned off.

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

Structure

Transistors usually include 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 job of the transistor depends on electrical signals to control its opening and closing, allowing fast switching operations.

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

Application areas

Transistors are widely used in amplification, switches, oscillators, and other elements of electronic circuits.

Thyristors are mainly utilized in electronic circuits including 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 attain current amplification.

The thyristor is excited 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 may be used in similar applications in some cases, because of their different structures and operating principles, they have noticeable variations in performance and utilize occasions.

Application scope of thyristor

• In power electronic equipment, thyristors may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors may be used in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors may be used to control the current flow towards the heating element.
• In electric vehicles, transistors may 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, that is fully involved in the development of power industry, intelligent operation and maintenance management of 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.