Silicon-Controlled Rectifiers: The Backbone of Power Electronics

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What exactly is a thyristor?

A thyristor is really a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of 4 quantities of semiconductor components, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles would be the critical parts in 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 widely used in various electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a Thyristor is usually represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The working condition in the thyristor is that when 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 in the power supply, as well as the cathode is connected to the negative pole in the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), as well as the indicator light will not illuminate. This shows that the thyristor is not conducting and it has forward blocking capability.

  1. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is applied towards the control electrode (referred to as a trigger, as well as the applied voltage is called trigger voltage), the indicator light switches on. Because of this the transistor can control conduction.

  1. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, even if the voltage on the control electrode is taken away (that is certainly, K is turned on again), the indicator light still glows. This shows that the thyristor can continue to conduct. At this time, to be able to cut off the conductive thyristor, the power supply Ea should be cut off or reversed.

  1. 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, as well as the indicator light will not illuminate at the moment. This shows that the thyristor is not conducting and may reverse blocking.

  1. To sum up

1) Once the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state whatever voltage the gate is put through.

2) Once the thyristor is put through a forward anode voltage, the thyristor will only conduct once the gate is put through a forward voltage. At this time, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is turned on, provided that you will find a specific forward anode voltage, the thyristor will stay turned on no matter 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) Once the thyristor is on, as well as the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

5) The disorder for the thyristor to conduct is that a forward voltage ought to be applied between the anode as well as the cathode, and an appropriate forward voltage ought to be applied between the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage between the anode and cathode should be cut off, or the voltage should be reversed.

Working principle of thyristor

A thyristor is essentially an exclusive triode composed of three PN junctions. It may be equivalently viewed as composed of a PNP transistor (BG2) and an NPN transistor (BG1).

  1. In case a forward voltage is applied between the anode and cathode in the thyristor without applying a forward voltage towards 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 applied towards the control electrode at the moment, BG1 is triggered to create a base 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 will be introduced the collector of BG2. This current is delivered to BG1 for amplification and after that delivered 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 large current appears within the emitters of the two transistors, that is certainly, the anode and cathode in the thyristor (how big the current is actually dependant on how big the load and how big Ea), therefore the thyristor is completely turned on. This conduction process is finished in an exceedingly short period of time.
  2. After the thyristor is turned on, its conductive state will be maintained through the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is still within the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to change on. After the thyristor is turned on, the control electrode loses its function.
  3. The only way to switch off the turned-on thyristor is to reduce the anode current that it is insufficient to maintain the positive feedback process. The way to reduce the anode current is to cut off the forward power supply Ea or reverse the bond of Ea. The minimum anode current needed to keep your thyristor within the conducting state is called the holding current in the thyristor. Therefore, strictly speaking, provided that the anode current is under the holding current, the thyristor may be turned off.

What is the difference between a transistor along with a thyristor?

Structure

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

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

Working conditions:

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

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

Application areas

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

Thyristors are mainly utilized in electronic circuits including 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 accomplish current amplification.

The thyristor is turned on or off by managing the trigger voltage in the control electrode to understand 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 sometimes, because of the different structures and working principles, they may have noticeable variations 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 may 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 really is one in the leading enterprises in the Home Accessory & Solar Power System, which can be fully involved in the development of power industry, intelligent operation and maintenance management of power plants, solar panel and related solar products manufacturing.

It accepts payment via Credit 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.