What exactly is a thyristor?

A thyristor is a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor materials, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles would be the critical parts from 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 working status. Therefore, thyristors are commonly used in a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the 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 working condition from 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 attached to the favorable pole from the power supply, and also the cathode is connected to the negative pole from the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), and also the indicator light does not illuminate. This demonstrates 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 applied towards the control electrode (called a trigger, and also the applied voltage is called 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 turned on, whether or not the voltage on the control electrode is taken off (which is, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can carry on and conduct. At this time, 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 towards the control electrode, a reverse voltage is applied between the anode and cathode, and also the indicator light does not illuminate at the moment. This demonstrates 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 whatever voltage the gate is exposed to.

2) If the thyristor is exposed to a forward anode voltage, the thyristor will only conduct when the gate is exposed to a forward voltage. At this time, the thyristor is incorporated in the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) If the thyristor is turned on, provided that there exists a specific forward anode voltage, the thyristor will always be turned on whatever the gate voltage. That is, following 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 your thyristor to conduct is the fact that a forward voltage needs to be applied between the anode and also the cathode, as well as an appropriate forward voltage also need to be applied between the gate and also the cathode. To turn off a conducting thyristor, the forward voltage between the anode and cathode must be shut down, or the voltage must be reversed.

Working principle of thyristor

A thyristor is actually an exclusive triode composed of three PN junctions. It could be equivalently regarded as comprising a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is applied between the anode and cathode from the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still switched off because BG1 has no base current. If a forward voltage is applied towards the control electrode at the moment, BG1 is triggered to generate a base 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 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 a crucial positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A sizable current appears in the emitters of the two transistors, which is, the anode and cathode from the thyristor (the size of the current is really dependant on the size of the stress and the size of Ea), so the thyristor is entirely turned on. This conduction process is finished in a really short time.
2. Following the thyristor is turned on, its conductive state is going to be maintained from the positive feedback effect from the tube itself. Even if the forward voltage from the control electrode disappears, it really is still in the conductive state. Therefore, the purpose of the control electrode is only to trigger the thyristor to turn on. After the thyristor is turned on, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor is always to reduce the anode current that it is not enough 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 bond of Ea. The minimum anode current necessary to keep your thyristor in the conducting state is called the holding current from the thyristor. Therefore, strictly speaking, provided that the anode current is less than the holding current, the thyristor may be switched off.

Exactly what is the distinction between a transistor as well as a thyristor?

Structure

Transistors usually consist of 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 the 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 in the gate to turn 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 like 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 turned on or off by controlling the trigger voltage from the control electrode to understand 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 may be used in similar applications in some instances, because of the different structures and working principles, they may 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-weight control devices.
• In induction cookers and electric water heaters, thyristors could 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 an excellent thyristor supplier. It is one from the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the development of power industry, intelligent operation and maintenance management of 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.