Just what is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four quantities of semiconductor components, including three PN junctions corresponding for 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 functioning status. Therefore, thyristors are commonly used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any semiconductor device is generally 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 light-weight-controlled thyristors. The functioning condition in the thyristor is the fact each time a forward voltage is used, 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 in between the anode and cathode (the anode is linked to the favorable pole in the power supply, and also the cathode is attached to the negative pole in the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and also the indicator light will not illuminate. This shows that the thyristor is not conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is used for the control electrode (known as a trigger, and also the applied voltage is known as trigger voltage), the indicator light turns on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after the thyristor is turned on, even when the voltage around the control electrode is taken off (that is certainly, K is turned on again), the indicator light still glows. This shows that the thyristor can still conduct. At the moment, in order 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 used for the control electrode, a reverse voltage is used in between the anode and cathode, and also the indicator light will not illuminate currently. This shows that the thyristor is not conducting and will reverse blocking.

5. In summary

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state regardless of 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. At the moment, the thyristor is incorporated in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) If the thyristor is turned on, provided that there exists a specific forward anode voltage, the thyristor will stay turned on regardless of the gate voltage. That is, after the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

4) If the thyristor is on, and also 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 a forward voltage should be applied in between the anode and also the cathode, as well as an appropriate forward voltage ought to be applied in between the gate and also the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode must be shut down, or perhaps the voltage must be reversed.

Working principle of thyristor

A thyristor is basically an exclusive triode made up of three PN junctions. It may be equivalently viewed as composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is used in 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 continues to be switched off because BG1 has no base current. In case a forward voltage is used for the control electrode currently, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in their collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current will be brought in the collector of BG2. This current is sent to BG1 for amplification and then sent to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A sizable current appears within the emitters of the two transistors, that is certainly, the anode and cathode in the thyristor (the size of the current is in fact determined by the size of the stress and the size of Ea), and so the thyristor is totally turned on. This conduction process is done in an exceedingly short period of time.
2. Right after the thyristor is turned on, its conductive state will be maintained from the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is still within the conductive state. Therefore, the purpose of the control electrode is only to trigger the thyristor to transform on. When the thyristor is turned on, the control electrode loses its function.
3. The only method to switch off the turned-on thyristor is always to reduce the anode current that it is insufficient to keep the positive feedback process. The way to reduce the anode current is always to shut down the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep your thyristor within 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 can be switched off.

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

Structure

Transistors usually consist of a PNP or NPN structure made up 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 job of any transistor relies on electrical signals to control its closing and opening, allowing fast switching operations.

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

Application areas

Transistors are commonly used in amplification, switches, oscillators, along with other aspects of electronic circuits.

Thyristors are mainly 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 turned on or off by managing the trigger voltage in the control electrode to understand 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 sum up, although transistors and thyristors can be used in similar applications in some instances, due to their different structures and functioning principles, they have got noticeable variations in performance and use 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 light-weight control devices.
• In induction cookers and electric water heaters, thyristors can 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 is actually 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 control over power plants, solar power 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.