Silicon-Controlled Rectifiers: Empowering Electronics

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So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains 4 quantities of semiconductor materials, including 3 PN junctions corresponding for 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 functioning status. Therefore, thyristors are popular in a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the silicon-controlled rectifier is usually represented by 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 light-controlled thyristors. The functioning 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 used involving the anode and cathode (the anode is linked 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 used for the control pole (i.e., K is disconnected), as well as the indicator light does not illuminate. This demonstrates that the thyristor is not conducting and contains forward blocking capability.

  1. Controllable conduction

As shown in Figure b above, when K is closed, and a forward voltage is used for the control electrode (known as a trigger, as well as the applied voltage is called trigger voltage), the indicator light turns on. This means that the transistor can control conduction.

  1. Continuous conduction

As shown in Figure c above, after the thyristor is switched on, even when the voltage on the control electrode is removed (that is, K is switched on again), the indicator light still glows. This demonstrates that the thyristor can carry on and conduct. At the moment, to be able to stop the conductive thyristor, the power supply Ea has to be stop 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 involving the anode and cathode, as well as the indicator light does not illuminate currently. This demonstrates that the thyristor is not conducting and will reverse blocking.

  1. To sum up

1) If 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) 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. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is switched on, so long as you will find a specific forward anode voltage, the thyristor will remain switched on no matter the gate voltage. That is certainly, after the thyristor is switched on, the gate will lose its function. The gate only serves as a trigger.

4) If the thyristor is on, as well as 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 needs to be applied involving the anode as well as the cathode, plus an appropriate forward voltage ought to be applied involving the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode has to be stop, or perhaps the voltage has to be reversed.

Working principle of thyristor

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

  1. In case a forward voltage is used involving 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 continues to be switched off because BG1 has no base current. In case a forward voltage is used for the control electrode currently, BG1 is triggered to generate a base 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 be introduced 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 in a saturated conduction state quickly. A sizable current appears inside the emitters of the two transistors, that is, the anode and cathode in the thyristor (the size of the current is actually based on the size of the burden and the size of Ea), so the thyristor is entirely switched on. This conduction process is done in a really short time.
  2. Following the thyristor is switched on, its conductive state will be maintained by the positive feedback effect in the tube itself. Even when the forward voltage in the control electrode disappears, it is actually still inside the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. Once the thyristor is switched on, the control electrode loses its function.
  3. The only way to shut off the turned-on thyristor is to decrease the anode current that it is not enough to keep the positive feedback process. How you can decrease the anode current is to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to maintain the thyristor inside the conducting state is called 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 switched off.

What exactly is the distinction between a transistor and a thyristor?

Structure

Transistors usually contain 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 task of the transistor relies on electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor demands 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 aspects of electronic circuits.

Thyristors are mainly utilized in electronic circuits like 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 attain current amplification.

The thyristor is switched 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 sum up, although transistors and thyristors can be used in similar applications in some cases, due to their different structures and functioning principles, they have noticeable differences in performance and use occasions.

Application scope of thyristor

  • In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
  • In the lighting field, thyristors can be used in dimmers and light 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 a wonderful thyristor supplier. It really is one in 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 control over power plants, solar panel 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.