What is a thyristor?

A thyristor is a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure includes 4 quantities of semiconductor elements, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles would be 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 operating status. Therefore, thyristors are widely used in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the semiconductor device is generally 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 lightweight-controlled thyristors. The operating condition in the thyristor is the fact each time 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 utilized involving the anode and cathode (the anode is connected to the favorable pole in the power supply, and also the cathode is connected to the negative pole in the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and also the indicator light fails to light up. This shows that the thyristor will not be 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 to the control electrode (referred to as a trigger, and also the applied voltage is called trigger voltage), the indicator light switches on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is excited, even when the voltage in the control electrode is taken away (which is, K is excited again), the indicator light still glows. This shows that the thyristor can continue to conduct. Currently, to be able to shut down the conductive thyristor, the power supply Ea must be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is applied to the control electrode, a reverse voltage is applied involving the anode and cathode, and also the indicator light fails to light up at this time. This shows that the thyristor will not be conducting and may reverse blocking.

5. To sum up

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 will only conduct when the gate is exposed to a forward voltage. Currently, the thyristor is within the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) When the thyristor is excited, so long as there exists a specific forward anode voltage, the thyristor will remain excited no matter the gate voltage. That is, following the thyristor is excited, the gate will lose its function. The gate only functions as a trigger.

4) When the thyristor is on, and also the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

5) The disorder for your thyristor to conduct is the fact a forward voltage should be applied involving the anode and also the cathode, as well as an appropriate forward voltage should also be applied involving the gate and also the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode must be shut down, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is actually a unique triode made up of three PN junctions. It could be equivalently viewed as consisting of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is applied involving the anode and cathode in the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be switched off because BG1 has no base current. In case a forward voltage is applied to the control electrode at this time, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in their collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current is going to be introduced the collector of BG2. This current is brought to BG1 for amplification then brought to BG2 for amplification again. Such repeated amplification forms a crucial positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A large current appears within the emitters of these two transistors, which is, the anode and cathode in the thyristor (how big the current is actually determined by how big the stress and how big Ea), so the thyristor is completely excited. This conduction process is completed in a really limited time.
2. After the thyristor is excited, its conductive state is going to be maintained from the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it really is still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to turn on. When the thyristor is excited, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor is always to reduce the anode current that it is not enough to keep up the positive feedback process. The way to reduce the anode current is always to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current required to keep the thyristor within the conducting state is called the holding current in the thyristor. Therefore, strictly speaking, so long as the anode current is less than the holding current, the thyristor could be switched off.

What exactly is the distinction between a transistor and a thyristor?

Structure

Transistors usually contain a PNP or NPN structure made up 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 demands a forward voltage and a trigger current in the gate to turn on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, along with other facets of electronic circuits.

Thyristors are mostly found in electronic circuits such as 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 attain current amplification.

The thyristor is excited or off by manipulating the trigger voltage in the control electrode to comprehend the switching function.

Circuit parameters

The circuit parameters of thyristors are based on 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 in some instances, because of their different structures and operating principles, they have noticeable differences 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.
• Inside the lighting field, thyristors can be utilized in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors could be used to control the current flow to the heating element.
• In electric vehicles, transistors can be utilized in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It really is one in the leading enterprises in the Home Accessory & Solar Power System, which is fully working in the progression of power industry, intelligent operation and maintenance control over power plants, solar power 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.