Just what is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor elements, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles would be 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 widely used in various electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a semiconductor device is normally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The working condition from the thyristor is the fact when 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 from the power supply, and also the cathode is linked to the negative pole from the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light will not illuminate. This implies that the thyristor is not really 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 used towards the control electrode (referred to as a trigger, and also the applied voltage is known as trigger voltage), the indicator light turns on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, 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 implies that the thyristor can still conduct. Currently, so that you can shut down the conductive thyristor, the power supply Ea has to be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used towards the control electrode, a reverse voltage is used between the anode and cathode, and also the indicator light will not illuminate currently. This implies that the thyristor is not really conducting and may reverse blocking.

5. In conclusion

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is within 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. Currently, the thyristor is in the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is turned on, provided that there exists a specific forward anode voltage, the thyristor will always be turned on no matter the gate voltage. Which is, after the thyristor is turned on, the gate will lose its function. The gate only functions as a trigger.

4) If 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 a forward voltage needs to be applied between the anode and also the cathode, as well as an appropriate forward voltage should also be applied between the gate and also the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode has to be shut down, or the voltage has to be reversed.

Working principle of thyristor

A thyristor is essentially a distinctive triode composed of three PN junctions. It can be equivalently regarded as comprising a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is used between the anode and cathode from the thyristor without applying a forward voltage towards 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. In case a forward voltage is used towards the control electrode currently, BG1 is triggered to produce 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 is going to be brought in 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 big current appears within the emitters of the two transistors, that is, the anode and cathode from the thyristor (the size of the current is in fact determined by the size of the burden and the size of Ea), so the thyristor is entirely turned on. This conduction process is finished in an exceedingly short time.
2. After the thyristor is turned on, its conductive state is going to be maintained from the positive feedback effect from the tube itself. Whether or not the forward voltage from the control electrode disappears, it is still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to turn on. When the thyristor is turned on, the control electrode loses its function.
3. The best way to shut off the turned-on thyristor is always to reduce the anode current that it is insufficient to keep up the positive feedback process. The way to reduce the anode current is always to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current required to maintain the thyristor within 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 can be turned off.

What exactly is the distinction between a transistor and 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 work of a transistor relies upon 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 turn on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, as well as other elements of electronic circuits.

Thyristors are mostly utilized in electronic circuits like controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Method 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 controlling the trigger voltage from 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 sum up, although transistors and thyristors may be used in similar applications in some instances, 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 may be used to control the current flow towards the heating element.
• In electric vehicles, transistors may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is actually one from the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the progression of power industry, intelligent operation and maintenance control over power plants, solar power 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.