What exactly is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains four levels of semiconductor materials, including three PN junctions corresponding towards 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 widely used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the silicon-controlled rectifier is normally represented by 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 operating condition in the thyristor is the fact 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 is used in between the anode and cathode (the anode is attached to the favorable pole in the power supply, and also the cathode is connected to the negative pole in the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light does not illuminate. This implies 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, and a forward voltage is used towards the control electrode (known as a trigger, and also the applied voltage is referred to as trigger voltage), the indicator light switches on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after the thyristor is turned on, whether or not the voltage on the control electrode is taken off (that is certainly, K is turned on again), the indicator light still glows. This implies that the thyristor can continue to conduct. Currently, 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 used towards the control electrode, a reverse voltage is used in between the anode and cathode, and also the indicator light does not illuminate at the moment. This implies that the thyristor is not really conducting and may reverse blocking.

5. In summary

1) Once the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state whatever voltage the gate is put through.

2) Once the thyristor is put through a forward anode voltage, the thyristor is only going to conduct if the gate is put through a forward voltage. Currently, the thyristor is within the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is turned on, as long as there is a specific forward anode voltage, the thyristor will always be turned on whatever the gate voltage. That is certainly, after the thyristor is turned on, 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 disorder for that thyristor to conduct is the fact a forward voltage needs to be applied in between the anode and also the cathode, plus an appropriate forward voltage also need to be applied in between the gate and also the cathode. To turn off a conducting thyristor, the forward voltage in between the anode and cathode must be cut off, or the voltage must be reversed.

Working principle of thyristor

A thyristor is actually a unique triode composed of three PN junctions. It can be equivalently viewed as comprising a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If a forward voltage is used in between the anode and cathode in 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. If a forward voltage is used towards the control electrode at the moment, BG1 is triggered to produce a base 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 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 enter a saturated conduction state quickly. A sizable current appears within the emitters of these two transistors, that is certainly, the anode and cathode in the thyristor (how big the current is really determined by how big the burden and how big Ea), therefore the thyristor is completely turned on. This conduction process is done in an exceedingly short period of time.
2. Right after the thyristor is turned on, its conductive state will be maintained by the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is actually still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to turn on. After the thyristor is turned on, the control electrode loses its function.
3. The only method to turn off the turned-on thyristor would be to reduce the anode current that it is insufficient to maintain the positive feedback process. The best way to reduce the anode current would be to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep your thyristor within the conducting state is referred to 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 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.

Working conditions:

The work of the transistor relies on electrical signals to control its opening and closing, allowing fast switching operations.

The thyristor needs 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 aspects of electronic circuits.

Thyristors are mostly used in electronic circuits such as 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 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 in most cases have higher turn-off voltage and larger on-current.

To sum up, although transistors and thyristors may be used in similar applications in some cases, 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 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 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 a superb thyristor supplier. It is actually one in the leading enterprises in the Home Accessory & Solar Power System, which can be fully active in the progression of power industry, intelligent operation and maintenance management of 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. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.