What is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure contains 4 levels 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, 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 functioning status. Therefore, thyristors are popular in a variety of electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any Thyristor 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 light-controlled thyristors. The functioning condition in the thyristor is that each time a forward voltage is applied, the gate needs 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 connected 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 applied for the control pole (i.e., K is disconnected), as well as the indicator light fails to illuminate. This shows that the thyristor is not really 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 applied for the control electrode (called a trigger, as well as the applied voltage is known as trigger voltage), the indicator light switches on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after the thyristor is switched on, even when the voltage in the control electrode is removed (that is certainly, K is switched on again), the indicator light still glows. This shows that the thyristor can continue to conduct. At the moment, to be able 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 applied for the control electrode, a reverse voltage is applied in between the anode and cathode, as well as the indicator light fails to illuminate currently. This shows that the thyristor is not really conducting and will reverse blocking.

5. In summary

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is exposed to.

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

3) If the thyristor is switched on, as long as you will find a specific forward anode voltage, the thyristor will remain switched on no matter the gate voltage. Which is, after the thyristor is switched 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 close to zero, the thyristor turns off.

5) The condition 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 must be cut off, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is basically a distinctive triode composed of three PN junctions. It may be equivalently regarded as consisting of a PNP transistor (BG2) and an NPN transistor (BG1).

1. If a forward voltage is applied in 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 remains switched off because BG1 has no base current. If a forward voltage is applied for the control electrode currently, BG1 is triggered to generate 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 will likely be introduced the collector of BG2. This current is delivered to BG1 for amplification and after that delivered 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 large current appears inside the emitters of the two transistors, that is certainly, the anode and cathode in the thyristor (how big the current is in fact determined by how big the load and how big Ea), so the thyristor is entirely switched on. This conduction process is finished in an exceedingly short time.
2. Right after the thyristor is switched 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 still inside the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to transform on. Once the thyristor is switched on, the control electrode loses its function.
3. The only method to shut off the turned-on thyristor would be to decrease the anode current that it is insufficient to maintain the positive feedback process. The way to decrease the anode current would be to cut off the forward power supply Ea or reverse the bond of Ea. The minimum anode current needed to keep the thyristor inside the conducting state is known as the holding current in the thyristor. Therefore, as it happens, as long as the anode current is less 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 contain a PNP or NPN structure composed of three semiconductor materials.

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

Operating conditions:

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

The thyristor requires a forward voltage as well as a trigger current at the gate to transform 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 such as 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 controlling the trigger voltage in the control electrode to understand the switching function.

Circuit parameters

The circuit parameters of thyristors are related to stability and reliability and usually have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors can be used in similar applications in some instances, due to their different structures and functioning principles, they may 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.
• Within the lighting field, thyristors can be used in dimmers and light 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, that is fully involved in the development of power industry, intelligent operation and maintenance handling of power plants, solar power 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.