So what is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor elements, including three PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These three poles are definitely the critical parts from 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 popular in various 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 also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The working condition from the thyristor is the fact that whenever 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 between the anode and cathode (the anode is connected to the favorable pole from the power supply, and also the cathode is connected to the negative pole from the power supply). But no forward voltage is applied for the control pole (i.e., K is disconnected), and also the indicator light will not light up. This shows that the thyristor is not conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, and a forward voltage is applied for the control electrode (known as a trigger, and also the applied voltage is known as trigger voltage), the indicator light switches on. Which means that 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 removed (that is certainly, K is excited again), the indicator light still glows. This shows that the thyristor can still conduct. Currently, to be able to cut off the conductive thyristor, the power supply Ea should 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 between the anode and cathode, and also the indicator light will not light up at this time. This shows that the thyristor is not conducting and can reverse blocking.

5. In conclusion

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

2) Once the thyristor is exposed to a forward anode voltage, the thyristor will simply conduct when the gate is exposed to a forward voltage. Currently, the thyristor is incorporated in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is excited, provided that you will find a specific forward anode voltage, the thyristor will always be excited regardless of the gate voltage. Which is, right after the thyristor is excited, the gate will lose its function. The gate only works as a trigger.

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

5) The condition for the thyristor to conduct is the fact that a forward voltage needs to be applied between the anode and also the cathode, as well as an appropriate forward voltage also need to be applied between the gate and also the cathode. To transform off a conducting thyristor, the forward voltage between the anode and cathode should be cut off, or even the voltage should be reversed.

Working principle of thyristor

A thyristor is basically a distinctive triode made from three PN junctions. It can be equivalently regarded as consisting of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is applied between the anode and cathode from 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 applied for the control electrode at this time, BG1 is triggered to generate basics 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 delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A sizable current appears inside the emitters of the two transistors, that is certainly, the anode and cathode from the thyristor (the dimensions of the current is actually based on the dimensions of the stress and the dimensions of Ea), so the thyristor is completely excited. This conduction process is completed in a very short period of time.
2. Following the thyristor is excited, its conductive state will be maintained through the positive feedback effect from the tube itself. Whether or not the forward voltage from 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 change on. Once the thyristor is excited, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor would be to decrease the anode current so that it is insufficient to keep the positive feedback process. How you can 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 maintain the thyristor inside the conducting state is known as the holding current from the thyristor. Therefore, as it happens, provided that the anode current is less than the holding current, the thyristor could be switched off.

Exactly what is the difference between a transistor and a thyristor?

Structure

Transistors usually contain 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.

Functioning conditions:

The job of any transistor depends on electrical signals to control its opening and closing, 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 facets of electronic circuits.

Thyristors are mostly utilized 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 excited or off by controlling the trigger voltage from 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 instances, because of their different structures and working principles, they have got noticeable differences 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 could 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 is one from 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 panel and related solar products manufacturing.

It accepts payment via Credit 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.