Semiconductor Devices: Exploring Their Diversity

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Just what is a thyristor?

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

The graphical symbol of any semiconductor device is usually represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The working condition in the thyristor is that whenever a forward voltage is used, 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 in between the anode and cathode (the anode is linked to the favorable pole in the power supply, as well as the cathode is attached to the negative pole in the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), as well as the indicator light fails to illuminate. This shows that the thyristor is not conducting and has forward blocking capability.

  1. Controllable conduction

As shown in Figure b above, when K is closed, along with a forward voltage is used to the control electrode (called a trigger, as well as the applied voltage is known as trigger voltage), the indicator light turns 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, even if the voltage on the control electrode is removed (that is, K is turned on again), the indicator light still glows. This shows that the thyristor can continue to conduct. Currently, in order to cut off the conductive thyristor, the power supply Ea has to be cut off or reversed.

  1. Reverse blocking

As shown in Figure d above, although a forward voltage is used to the control electrode, a reverse voltage is used in between the anode and cathode, as well as the indicator light fails to illuminate currently. This shows that the thyristor is not conducting and will reverse blocking.

  1. In conclusion

1) If the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state regardless of 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 when the gate is put through a forward voltage. Currently, the thyristor is in the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is turned on, so long as you will find a specific forward anode voltage, the thyristor will always be turned on regardless of the gate voltage. That is certainly, right 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, as well as the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.

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

Working principle of thyristor

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

  1. When a forward voltage is used in between the anode and cathode in 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. When a forward voltage is used to the control electrode currently, BG1 is triggered to produce a base current Ig. BG1 amplifies this current, along with 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 brought in the collector of BG2. This current is sent to BG1 for amplification and then sent 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, the anode and cathode in the thyristor (how big the current is really determined by how big the burden and how big Ea), and so the thyristor is completely turned on. This conduction process is finished in a really limited time.
  2. Following the thyristor is turned 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 within the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to transform on. Once the thyristor is turned on, the control electrode loses its function.
  3. The only way to shut off the turned-on thyristor is to decrease the anode current so that it is not enough to maintain the positive feedback process. How you can decrease the anode current is to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current required to keep your thyristor within the conducting state is known as the holding current in the thyristor. Therefore, strictly speaking, so long as the anode current is lower than 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 made from three semiconductor materials.

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

Working conditions:

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

The thyristor demands a forward voltage along with a trigger current on the gate to transform on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, and other facets of electronic circuits.

Thyristors are mainly used 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 attain current amplification.

The thyristor is turned on or off by managing the trigger voltage in the control electrode to comprehend the switching function.

Circuit parameters

The circuit parameters of thyristors are related to stability and reliability and often 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 have noticeable differences in performance and use 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 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 may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is one in the leading enterprises in the Home Accessory & Solar Power System, which is fully working in the development of power industry, intelligent operation and maintenance control over 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.