What is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes 4 levels of semiconductor materials, including three PN junctions corresponding for 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 working status. Therefore, thyristors are popular in different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any Thyristor is normally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The working condition of the thyristor is the fact that whenever 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 in between the anode and cathode (the anode is connected 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 used for the control pole (i.e., K is disconnected), as well as the indicator light will not glow. 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 used for the control electrode (called a trigger, as well as the applied voltage is known as trigger voltage), the indicator light switches on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, right after the thyristor is excited, whether or not the voltage in the control electrode is removed (that is certainly, K is excited again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At the moment, 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 used for the control electrode, a reverse voltage is used in between the anode and cathode, as well as the indicator light will not glow at the moment. This implies that the thyristor is not conducting and can reverse blocking.

5. In summary

1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is in a reverse blocking state regardless of what voltage the gate is subjected to.

2) Once the thyristor is subjected to a forward anode voltage, the thyristor will only conduct when the gate is subjected to a forward voltage. At the moment, the thyristor is in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is excited, provided that there is a specific forward anode voltage, the thyristor will stay excited regardless of the gate voltage. Which is, right after the thyristor is excited, the gate will lose its function. The gate only functions as a trigger.

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

5) The condition for the thyristor to conduct is the fact that 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 the voltage must be reversed.

Working principle of thyristor

A thyristor is actually an exclusive triode made up of three PN junctions. It can be equivalently thought to be composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. When a forward voltage is used in between the anode and cathode of 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 used for the control electrode at the moment, 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 delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A sizable current appears in the emitters of these two transistors, that is certainly, the anode and cathode of the thyristor (how big the current is really dependant on how big the load and how big Ea), so the thyristor is completely excited. This conduction process is completed in a really limited time.
2. Right after the thyristor is excited, its conductive state is going to be maintained from the positive feedback effect of the tube itself. Even if the forward voltage of the control electrode disappears, it really is still in the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to change on. When the thyristor is excited, the control electrode loses its function.
3. The only method to shut off the turned-on thyristor would be to decrease the anode current so that it is insufficient to keep the positive feedback process. The way to decrease the anode current would be to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep the thyristor in the conducting state is known as the holding current of the thyristor. Therefore, as it happens, provided that the anode current is lower than the holding current, the thyristor can be switched off.

What 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 task of any transistor depends on electrical signals to control its closing and opening, allowing fast switching operations.

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

Application areas

Transistors are popular in amplification, switches, oscillators, along with 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 attain current amplification.

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

Circuit parameters

The circuit parameters of thyristors are related to stability and reliability and in most cases have higher turn-off voltage and larger on-current.

To sum up, although transistors and thyristors can be used in similar applications in some instances, 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 used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors can be used in dimmers and lightweight 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 used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It really is one of the leading enterprises in the Home Accessory & Solar Power System, that is fully active 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 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.