What exactly is a thyristor?

A thyristor is really a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure includes four levels of semiconductor components, including three PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These three 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 operating status. Therefore, thyristors are popular in different electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any silicon-controlled rectifier is normally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The operating condition in the thyristor is the fact that whenever 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 involving the anode and cathode (the anode is attached to the favorable pole in the power supply, and also the cathode is linked to the negative pole in the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and also the indicator light will not illuminate. This implies that the thyristor is not conducting and contains forward blocking capability.

2. Controllable conduction

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

3. Continuous conduction

As shown in Figure c above, right after the thyristor is excited, whether or not the voltage on the control electrode is taken off (that is, K is excited again), the indicator light still glows. This implies that the thyristor can continue to conduct. At the moment, in order to cut off the conductive thyristor, the power supply Ea must be cut off or reversed.

4. 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, and also the indicator light will not illuminate at the moment. This implies that the thyristor is not conducting and can reverse blocking.

5. In summary

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

2) If the thyristor is exposed to a forward anode voltage, the thyristor is only going to conduct once the gate is exposed to a forward voltage. At the moment, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is excited, so long as there is a specific forward anode voltage, the thyristor will remain excited regardless of the gate voltage. That is, right after the thyristor is excited, the gate will lose its function. The gate only serves as a trigger.

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

5) The disorder for the thyristor to conduct is the fact that a forward voltage should be applied involving the anode and also the cathode, plus an appropriate forward voltage should also be applied involving the gate and also the cathode. To change off a conducting thyristor, the forward voltage involving the anode and cathode must be cut off, or the voltage must be reversed.

Working principle of thyristor

A thyristor is actually an exclusive triode made up of three PN junctions. It could be equivalently regarded as comprising a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If 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 is still switched off because BG1 has no base current. If a forward voltage is used for the control electrode at the moment, BG1 is triggered to produce a base 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 is going to 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 get in a saturated conduction state quickly. A big current appears inside the emitters of the two transistors, that is, the anode and cathode in the thyristor (the size of the current is really dependant on the size of the burden and the size of Ea), and so the thyristor is completely excited. This conduction process is finished in a very limited time.
2. Following the thyristor is excited, its conductive state is going to be maintained through the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is still inside the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to turn on. Once the thyristor is excited, the control electrode loses its function.
3. The best way to turn off the turned-on thyristor is always to lessen the anode current that it is inadequate to maintain the positive feedback process. The best way to lessen the anode current is always to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep the thyristor inside the conducting state is called the holding current in the thyristor. Therefore, strictly speaking, so long as the anode current is lower than the holding current, the thyristor can be switched off.

Exactly what is the difference between a transistor as well as a thyristor?

Structure

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

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

Working conditions:

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

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

Application areas

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

Thyristors are mainly found 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 excited or off by managing the trigger voltage in the control electrode to comprehend 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 instances, due to 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 can 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 involved in the growth and development of power industry, intelligent operation and maintenance control over power plants, solar power 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.