So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure contains 4 levels of semiconductor elements, including three PN junctions corresponding to 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 functioning status. Therefore, thyristors are widely used in different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any silicon-controlled rectifier is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, 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 can be used 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 does not illuminate. This implies that the thyristor will not be conducting and it has forward blocking capability.

2. 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.

3. Continuous conduction

As shown in Figure c above, following the thyristor is excited, whether or not the voltage in the control electrode is taken away (that is certainly, K is excited again), the indicator light still glows. This implies that the thyristor can carry on and conduct. Currently, to be able to shut down the conductive thyristor, the power supply Ea must be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used to the control electrode, a reverse voltage is used between the anode and cathode, as well as the indicator light does not illuminate at the moment. This implies that the thyristor will not be conducting and can reverse blocking.

5. In conclusion

1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is at a reverse blocking state regardless of what voltage the gate is subjected to.

2) Once the thyristor is subjected to a forward anode voltage, the thyristor will only conduct when the gate is subjected to a forward voltage. Currently, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is excited, as long as there is a specific forward anode voltage, the thyristor will always be excited no matter the gate voltage. That is, following the thyristor is excited, the gate will lose its function. The gate only functions as a trigger.

4) Once 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 that thyristor to conduct is that a forward voltage ought to be applied between the anode as well as the cathode, and an appropriate forward voltage also need to be applied between the gate as well as the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode must be shut down, or even the voltage must be reversed.

Working principle of thyristor

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

1. If a forward voltage is used 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 remains switched off because BG1 has no base current. If a forward voltage is used to the control electrode at the moment, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, along with 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 an essential positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A sizable current appears in the emitters of the two transistors, that is certainly, the anode and cathode in the thyristor (the size of the current is really dependant on the size of the load and the size of Ea), and so the thyristor is totally excited. This conduction process is completed in a really limited time.
2. Following the thyristor is excited, its conductive state will likely be maintained through the positive feedback effect in the tube itself. Whether or not the forward voltage in the control electrode disappears, it is still in the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to transform on. After the thyristor is excited, 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 not enough to keep up the positive feedback process. The way to decrease the anode current would be to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to maintain the thyristor in the conducting state is known as the holding current in the thyristor. Therefore, as it happens, as long as the anode current is under the holding current, the thyristor may be switched off.

Exactly what is the distinction between a transistor along with a thyristor?

Structure

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

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

Operating 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 along with a trigger current in the gate to transform on or off.

Application areas

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

Thyristors are mainly utilized in electronic circuits including 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 realize the switching function.

Circuit parameters

The circuit parameters of thyristors are based on stability and reliability and usually 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, because of the different structures and functioning principles, they have got 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 to 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 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 handling of 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. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.