Just what is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor components, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles are the critical parts from 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 widely used in a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a semiconductor device is usually represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The working condition from the thyristor is the fact that when 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 can be used in between the anode and cathode (the anode is attached to the favorable pole from the power supply, and the cathode is connected to the negative pole from the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), and 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 used to the control electrode (referred to as a trigger, and the applied voltage is referred to as trigger voltage), the indicator light switches on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after the thyristor is switched on, even when the voltage around the control electrode is taken away (that is certainly, K is switched on again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. Currently, so that you can shut down the conductive thyristor, the power supply Ea should be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used to the control electrode, a reverse voltage is used in between the anode and cathode, and the indicator light does not illuminate at the moment. This demonstrates that the thyristor is not conducting and will reverse blocking.

5. In conclusion

1) Once 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) Once 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. Currently, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is switched on, so long as there exists a specific forward anode voltage, the thyristor will always be switched on no matter the gate voltage. That is certainly, after the thyristor is switched on, the gate will lose its function. The gate only functions as a trigger.

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

5) The disorder for your thyristor to conduct is the fact that a forward voltage should be applied in between the anode and the cathode, as well as an appropriate forward voltage also need to be applied in between the gate and the cathode. To transform off a conducting thyristor, the forward voltage in between the anode and cathode should be shut down, or perhaps the voltage should be reversed.

Working principle of thyristor

A thyristor is basically an exclusive triode composed of three PN junctions. It may be equivalently thought to be comprising 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 from the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still turned off because BG1 has no base current. In case a forward voltage is used to the control electrode at the moment, BG1 is triggered to produce a base current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in its 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 a crucial positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A big current appears inside the emitters of these two transistors, that is certainly, the anode and cathode from the thyristor (the size of the current is actually determined by the size of the stress and the size of Ea), and so the thyristor is totally switched on. This conduction process is done in a very short period of time.
2. After the thyristor is switched on, its conductive state is going to be maintained through the positive feedback effect from the tube itself. Even if the forward voltage from the control electrode disappears, it really is still inside the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to change on. Once the thyristor is switched on, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor is to lessen the anode current that it is not enough to keep the positive feedback process. The way to lessen the anode current is to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current necessary to keep the thyristor inside the conducting state is referred to as the holding current from the thyristor. Therefore, strictly speaking, so long as the anode current is lower than the holding current, the thyristor may be turned off.

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

Structure

Transistors usually contain 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.

Functioning conditions:

The work of a transistor relies on electrical signals to control its closing and opening, allowing fast switching operations.

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

Application areas

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

Thyristors are mainly found in electronic circuits like 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 switched on or off by controlling the trigger voltage from the control electrode to realize the switching function.

Circuit parameters

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

To summarize, although transistors and thyristors can be utilized in similar applications in some cases, because of their different structures and working principles, they have got 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.
• In the lighting field, thyristors can be utilized in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors can 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 wonderful thyristor supplier. It is actually one from the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the progression of power industry, intelligent operation and maintenance handling 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. If you are looking for high-quality thyristor, please feel free to contact us and send an inquiry.