So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure consists of four levels of semiconductor components, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles are 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 different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any silicon-controlled rectifier 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 light-weight-controlled thyristors. The operating condition in the thyristor is the fact that 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 between the anode and cathode (the anode is connected to the favorable pole in the power supply, as well as the cathode is connected to the negative pole in the power supply). But no forward voltage is applied for the control pole (i.e., K is disconnected), as well as the indicator light will not illuminate. This shows 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, along with a forward voltage is applied for the control electrode (known as a trigger, as well as the applied voltage is known as trigger voltage), the indicator light turns on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is excited, whether or not the voltage around the control electrode is removed (that is certainly, K is excited again), the indicator light still glows. This shows that the thyristor can continue to conduct. At this time, so that you can 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 for the control electrode, a reverse voltage is applied between the anode and cathode, as well as the indicator light will not illuminate at the moment. This shows that the thyristor is not really conducting and can reverse blocking.

5. To sum up

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

2) When the thyristor is put through a forward anode voltage, the thyristor will simply conduct if the gate is put through a forward voltage. At this time, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) When the thyristor is excited, provided that there is a specific forward anode voltage, the thyristor will always be excited whatever the gate voltage. That is certainly, following the thyristor is excited, the gate will lose its function. The gate only serves as a trigger.

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

5) The problem for the thyristor to conduct is the fact that a forward voltage ought to be applied between the anode as well as the cathode, and an appropriate forward voltage ought to be applied between the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage between the anode and cathode must be shut down, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is essentially a unique triode composed of three PN junctions. It may be equivalently viewed as composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. When a forward voltage is applied between 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. When a forward voltage is applied for the control electrode at the moment, BG1 is triggered to create a base current Ig. BG1 amplifies this current, along with 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 sent to BG1 for amplification then sent to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A large current appears inside the emitters of the two transistors, that is certainly, the anode and cathode in the thyristor (the size of the current is really based on the size of the burden and the size of Ea), therefore the thyristor is entirely excited. This conduction process is finished in a very short 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 inside the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to change on. After the thyristor is excited, the control electrode loses its function.
3. The only way to switch off the turned-on thyristor is to reduce the anode current so that it is not enough to keep the positive feedback process. How you can reduce the anode current is to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current necessary to maintain the thyristor inside the conducting state is known as the holding current in the thyristor. Therefore, strictly speaking, provided that the anode current is less than the holding current, the thyristor could be switched off.

Exactly what is the distinction between a transistor along with a thyristor?

Structure

Transistors usually include 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.

Working conditions:

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

The thyristor demands a forward voltage along with a trigger current at the gate to change on or off.

Application areas

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

Thyristors are mostly found 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 excited or off by controlling the trigger voltage in the control electrode to realize 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 in some instances, because of the different structures and operating principles, they may have noticeable differences in performance and utilize 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 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 really is one in the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the progression 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. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.