Just what is a thyristor?

A thyristor is really a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes 4 quantities of semiconductor materials, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 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 operating status. Therefore, thyristors are popular 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 by 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 lightweight-controlled thyristors. The operating condition from the thyristor is the fact that when 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 can be used involving the anode and cathode (the anode is attached to the favorable pole from the power supply, and the cathode is attached to the negative pole from the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and the indicator light fails to illuminate. This shows that the thyristor will not be 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 for the control electrode (known as a trigger, and the applied voltage is known as trigger voltage), the indicator light switches on. Because of this 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, K is excited again), the indicator light still glows. This shows that the thyristor can carry on and conduct. Currently, in order to 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 involving the anode and cathode, and the indicator light fails to illuminate currently. This shows that the thyristor will not be conducting and will reverse blocking.

5. In conclusion

1) Once the thyristor is exposed to a reverse anode voltage, the thyristor is within a reverse blocking state whatever voltage the gate is exposed to.

2) Once the thyristor is exposed to a forward anode voltage, the thyristor will only conduct when the gate is exposed to a forward voltage. Currently, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) Once the thyristor is excited, as long as there is a specific forward anode voltage, the thyristor will stay excited regardless of the gate voltage. That is certainly, 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, and the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.

5) The condition for that thyristor to conduct is the fact that a forward voltage should be applied involving the anode and the cathode, plus an appropriate forward voltage should also be applied involving the gate and the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode must be cut off, or even the voltage must be reversed.

Working principle of thyristor

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

1. In case a forward voltage is used involving the anode and cathode from the thyristor without applying a forward voltage for the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains turned off because BG1 has no base current. In case a forward voltage is used for the control electrode currently, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, along with 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 these two transistors, that is, the anode and cathode from the thyristor (the dimensions of the current is in fact dependant on the dimensions of the load and the dimensions of Ea), and so the thyristor is totally excited. This conduction process is finished in a really short time.
2. After the thyristor is excited, its conductive state is going to be maintained by the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it is actually still in the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to change on. Once the thyristor is excited, the control electrode loses its function.
3. The best way to shut off the turned-on thyristor would be to reduce the anode current so that it is not enough to maintain the positive feedback process. How you can reduce the anode current would be to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current required to keep your thyristor in the conducting state is known as the holding current from the thyristor. Therefore, strictly speaking, as long as the anode current is lower than the holding current, the thyristor may be turned off.

What exactly is the distinction between a transistor along with 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 work of any transistor relies on electrical signals to control its closing and opening, allowing fast switching operations.

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

Application areas

Transistors are popular in amplification, switches, oscillators, and other elements of electronic circuits.

Thyristors are mostly found in electronic circuits such as 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 accomplish current amplification.

The thyristor is excited 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 sum up, although transistors and thyristors may be used in similar applications in some instances, because of their different structures and operating principles, they have got noticeable differences 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.
• Inside the lighting field, thyristors may be used in dimmers and lightweight 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 may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It really 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 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.