Reversely Switching Dynistors: A Breakthrough in Semiconductor Design

So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known 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 definitely 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 popular in a variety of electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a Thyristor is generally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The working condition from the thyristor is the fact that whenever a forward voltage is applied, the gate should have a trigger current.

Characteristics of thyristor

  1. Forward blocking

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

  1. Controllable conduction

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

  1. Continuous conduction

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

  1. Reverse blocking

As shown in Figure d above, although a forward voltage is applied for the control electrode, a reverse voltage is applied involving the anode and cathode, and also the indicator light will not light up currently. This demonstrates that the thyristor is not really conducting and may reverse blocking.

  1. In summary

1) If the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is put through.

2) If the thyristor is put through a forward anode voltage, the thyristor is only going to conduct once the gate is put through a forward voltage. Currently, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is switched on, provided that you will find a specific forward anode voltage, the thyristor will always be switched on whatever the gate voltage. That is, right after the thyristor is switched 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 the thyristor to conduct is the fact that a forward voltage should be applied involving the anode and also the cathode, as well as an appropriate forward voltage also need to be applied involving the gate and also the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode should be stop, or the voltage should be reversed.

Working principle of thyristor

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

  1. If a forward voltage is applied 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. If a forward voltage is applied for the control electrode currently, BG1 is triggered to create basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in their collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current is going to be brought in the collector of BG2. This current is delivered to BG1 for amplification and then delivered to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A sizable current appears in the emitters of the two transistors, that is, the anode and cathode from the thyristor (the dimensions of the current is really determined by the dimensions of the burden and the dimensions of Ea), and so the thyristor is totally switched on. This conduction process is done in a really limited time.
  2. Following the thyristor is switched on, its conductive state is going to be maintained from the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it is still in the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to transform on. After the thyristor is switched on, the control electrode loses its function.
  3. The best way to shut off the turned-on thyristor is always to lessen the anode current that it is insufficient to keep up the positive feedback process. How you can lessen the anode current is always to stop the forward power supply Ea or reverse the bond of Ea. The minimum anode current required to keep the thyristor in the conducting state is referred to as the holding current from the thyristor. Therefore, as it happens, provided that the anode current is less than the holding current, the thyristor may be turned off.

What is the distinction between a transistor and a thyristor?

Structure

Transistors usually consist of a PNP or NPN structure made from three semiconductor materials.

The thyristor is composed of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.

Operating conditions:

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

The thyristor needs a forward voltage and a trigger current at the gate to transform on or off.

Application areas

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

Thyristors are mainly used 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 switched on or off by managing 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 may be used in similar applications in some instances, due to their different structures and working principles, they may have noticeable differences in performance and make use of 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 could 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 an excellent thyristor supplier. It really is one from the leading enterprises in the Home Accessory & Solar Power System, that is fully active 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 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.