Just what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains four quantities of semiconductor elements, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles are the critical parts of 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 popular in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the silicon-controlled rectifier is normally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The functioning condition of the thyristor is the fact each time a forward voltage is used, the gate needs to have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage is utilized between the anode and cathode (the anode is connected to the favorable pole of the power supply, and also the cathode is linked to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light will not light up. This implies that the thyristor is not really conducting and has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is used towards the control electrode (referred to as a trigger, and also the applied voltage is referred to 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 turned on, whether or not the voltage on the control electrode is taken off (that is certainly, K is turned on again), the indicator light still glows. This implies that the thyristor can continue to conduct. At this time, in order to stop the conductive thyristor, the power supply Ea must be stop or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used towards the control electrode, a reverse voltage is used between the anode and cathode, and also the indicator light will not light up at this time. This implies that the thyristor is not really conducting and may reverse blocking.

5. In conclusion

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state no matter 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 this time, the thyristor is in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) If the thyristor is turned on, as long as you will find a specific forward anode voltage, the thyristor will remain turned on no matter the gate voltage. That is, following the thyristor is turned on, the gate will lose its function. The gate only works 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 a forward voltage needs to be applied between the anode and also the cathode, as well as an appropriate forward voltage ought to be applied between the gate and also the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode must be stop, or perhaps the voltage must be reversed.

Working principle of thyristor

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

1. In case a forward voltage is used between the anode and cathode of the thyristor without applying a forward voltage towards 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 towards the control electrode at this time, BG1 is triggered to generate 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 will likely be introduced the collector of BG2. This current is delivered to BG1 for amplification and then delivered to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A big current appears in the emitters of these two transistors, that is certainly, the anode and cathode of the thyristor (the size of the current is really based on the size of the load and the size of Ea), so the thyristor is entirely turned on. This conduction process is completed in an exceedingly limited time.
2. Following the thyristor is turned on, its conductive state will likely be maintained by the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it is actually still in the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to turn on. Once the thyristor is turned on, the control electrode loses its function.
3. The best way to turn off the turned-on thyristor would be to reduce the anode current that it is not enough to keep up the positive feedback process. The best way to reduce the anode current would be to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep the thyristor in the conducting state is referred to as the holding current of the thyristor. Therefore, as it happens, as long as the anode current is under the holding current, the thyristor can be turned off.

What exactly is the distinction between a transistor along with a thyristor?

Structure

Transistors usually contain a PNP or NPN structure made from 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 opening and closing, allowing fast switching operations.

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

Application areas

Transistors are popular in amplification, switches, oscillators, as well as other aspects of electronic circuits.

Thyristors are mainly utilized in electronic circuits such as controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Means 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 of the control electrode to comprehend 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 used in similar applications in some cases, because of their different structures and functioning principles, they have noticeable differences 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.
• Within 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 towards the heating element.
• In electric vehicles, transistors can be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a wonderful thyristor supplier. It is one of the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the growth and development of power industry, intelligent operation and maintenance management of 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.