Reversely Switching Dynistors: Changing the Game in Semiconductors

Posted on by

Specifically what is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor materials, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles would be 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 working status. Therefore, thyristors are popular in various electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a silicon-controlled rectifier is generally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The working condition from the thyristor is the fact that each time 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 can be used in between the anode and cathode (the anode is connected to the favorable pole from the power supply, and also the cathode is connected to the negative pole from the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and also the indicator light will not glow. This shows that the thyristor is not really conducting and contains forward blocking capability.

  1. Controllable conduction

As shown in Figure b above, when K is closed, and a forward voltage is applied to the control electrode (called a trigger, and also the applied voltage is called trigger voltage), the indicator light switches on. This means that the transistor can control conduction.

  1. Continuous conduction

As shown in Figure c above, right after the thyristor is turned on, whether or not the voltage around 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 carry on and conduct. At the moment, so that you can shut down the conductive thyristor, the power supply Ea must be shut down or reversed.

  1. Reverse blocking

As shown in Figure d above, although a forward voltage is applied to the control electrode, a reverse voltage is applied in between the anode and cathode, and also the indicator light will not glow at this time. This shows that the thyristor is not really conducting and can reverse blocking.

  1. To sum up

1) When the thyristor is put through a reverse anode voltage, the thyristor is within a reverse blocking state regardless of what voltage the gate is put through.

2) When the thyristor is put through a forward anode voltage, the thyristor will simply conduct if the gate is put through a forward voltage. At the moment, the thyristor is in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) When the thyristor is turned on, as long as there is a specific forward anode voltage, the thyristor will stay turned on no matter the gate voltage. Which is, right after the thyristor is turned on, the gate will lose its function. The gate only functions as a trigger.

4) When the thyristor is on, and also the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.

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

Working principle of thyristor

A thyristor is basically a distinctive triode made from three PN junctions. It could be equivalently thought to be consisting of a PNP transistor (BG2) plus an NPN transistor (BG1).

  1. In case a forward voltage is applied in between the anode and cathode from the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be turned off because BG1 has no base current. In case a forward voltage is applied to the control electrode at this time, 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 will likely be brought in the collector of BG2. This current is brought to BG1 for amplification and then brought 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 from the thyristor (the dimensions of the current is actually based on the dimensions of the stress and the dimensions of Ea), therefore the thyristor is completely turned on. This conduction process is finished in a very limited time.
  2. Following the thyristor is turned on, its conductive state will likely be maintained from the positive feedback effect from the tube itself. Whether or not the forward voltage from the control electrode disappears, it is actually still within the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to change on. Once the thyristor is turned on, the control electrode loses its function.
  3. The best way to switch 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 shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current needed to maintain the thyristor within the conducting state is called the holding current from the thyristor. Therefore, as it happens, as long as the anode current is under the holding current, the thyristor may be turned off.

What is the difference between a transistor and a thyristor?

Structure

Transistors usually consist of 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 work of a transistor relies upon electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor needs a forward voltage and a trigger current in the gate to change 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 like 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 achieve current amplification.

The thyristor is turned on or off by manipulating the trigger voltage from 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 summarize, although transistors and thyristors can be utilized in similar applications sometimes, due to their different structures and working principles, they have noticeable differences in performance and make use of occasions.

Application scope of thyristor

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

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is actually one from the leading enterprises in the Home Accessory & Solar Power System, which can be fully working in the progression of power industry, intelligent operation and maintenance management of power plants, solar 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.