High Frequency Thyristors: Bridging the Gap in Technology

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So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of 4 levels of semiconductor materials, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles are definitely 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 operating status. Therefore, thyristors are popular in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the semiconductor device is generally represented through 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 in the thyristor is that each time 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 is utilized between the anode and cathode (the anode is connected to the favorable pole in the power supply, and the cathode is connected to the negative pole in the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and the indicator light fails to glow. This implies that the thyristor will not be conducting and contains forward blocking capability.

  1. Controllable conduction

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

  1. Continuous conduction

As shown in Figure c above, after the thyristor is turned on, even if the voltage in the control electrode is removed (which is, K is turned on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. Currently, in order to shut down the conductive thyristor, the power supply Ea should be shut down or reversed.

  1. Reverse blocking

As shown in Figure d above, although a forward voltage is used for the control electrode, a reverse voltage is used between the anode and cathode, and the indicator light fails to glow at the moment. This implies that the thyristor will not be conducting and may reverse blocking.

  1. In summary

1) If the thyristor is subjected to a reverse anode voltage, the thyristor is in a reverse blocking state whatever voltage the gate is subjected to.

2) If the thyristor is subjected to a forward anode voltage, the thyristor will only conduct once the gate is subjected to a forward voltage. Currently, the thyristor is in the forward conduction state, which is the thyristor characteristic, which is, the controllable characteristic.

3) If the thyristor is turned on, so long as there exists a specific forward anode voltage, the thyristor will stay turned on regardless of the gate voltage. That is certainly, after 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 the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

5) The problem for that thyristor to conduct is that a forward voltage should be applied between the anode and the cathode, plus an appropriate forward voltage should also be applied between the gate and the cathode. To transform off a conducting thyristor, the forward voltage between the anode and cathode should be shut down, or even the voltage should be reversed.

Working principle of thyristor

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

  1. When a forward voltage is used between the anode and cathode in the thyristor without applying a forward voltage for the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still turned off because BG1 has no base current. When a forward voltage is used for the control electrode at the moment, BG1 is triggered to generate basics 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 will likely be brought in the collector of BG2. This current is brought to BG1 for amplification and after that brought to BG2 for amplification again. Such repeated amplification forms a crucial positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A sizable current appears within the emitters of the two transistors, which is, the anode and cathode in the thyristor (the size of the current is actually based on the size of the stress and the size of Ea), therefore the thyristor is entirely turned on. This conduction process is finished in a really limited time.
  2. Following the thyristor is turned on, its conductive state will likely be maintained through the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is actually still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to turn on. When the thyristor is turned on, the control electrode loses its function.
  3. The only method to turn off the turned-on thyristor would be to decrease the anode current that it is inadequate to keep up the positive feedback process. The way to decrease the anode current would be to shut down the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to maintain the thyristor within the conducting state is referred to as the holding current in the thyristor. Therefore, as it happens, so long as the anode current is lower than the holding current, the thyristor can be turned off.

What is the distinction between a transistor as well as a thyristor?

Structure

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

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

Functioning conditions:

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

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

Application areas

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

Thyristors are mainly utilized 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 accomplish current amplification.

The thyristor is turned on or off by controlling 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 often have higher turn-off voltage and larger on-current.

To sum up, although transistors and thyristors can be used in similar applications in some instances, because of their different structures and operating principles, they have got noticeable variations in performance and utilize occasions.

Application scope of thyristor

  • In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
  • Inside the lighting field, thyristors can be used in dimmers and lightweight control devices.
  • In induction cookers and electric water heaters, thyristors may be used to control the current flow for the heating element.
  • In electric vehicles, transistors can be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is one in the leading enterprises in the Home Accessory & Solar Power System, which is fully working in the progression of power industry, intelligent operation and maintenance management of power plants, solar power panel 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.