What exactly is a thyristor?

A thyristor is really a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure contains 4 quantities of semiconductor components, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles are definitely the critical parts from the thyristor, letting it 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 commonly used in a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any silicon-controlled rectifier is generally represented by 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 lightweight-controlled thyristors. The operating 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 in between the anode and cathode (the anode is attached to the favorable pole from the power supply, and the cathode is linked to the negative pole from the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and the indicator light does not illuminate. 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, along with a forward voltage is used for the control electrode (referred to as a trigger, and the applied voltage is referred to 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, 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 carry on and 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 used for the control electrode, a reverse voltage is used in between the anode and cathode, and the indicator light does not illuminate at the moment. This shows that the thyristor is not conducting and can reverse blocking.

5. In conclusion

1) When the thyristor is exposed to a reverse anode voltage, the thyristor is in a reverse blocking state whatever voltage the gate is exposed to.

2) When the thyristor is exposed to a forward anode voltage, the thyristor will only 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) When the thyristor is excited, as long as there is a specific forward anode voltage, the thyristor will remain excited no matter the gate voltage. That is certainly, right after the thyristor is excited, the gate will lose its function. The gate only functions as a trigger.

4) When the thyristor is on, and the primary circuit voltage (or current) decreases to seal 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 the cathode, and an appropriate forward voltage ought to be applied in between the gate and the cathode. To transform 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 actually a unique triode made up of three PN junctions. It can be equivalently regarded as consisting of a PNP transistor (BG2) and an NPN transistor (BG1).

1. If a forward voltage is used in 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. If a forward voltage is used for the control electrode at the moment, BG1 is triggered to produce basics 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 be introduced 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 vital positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A large current appears inside the emitters of these two transistors, that is certainly, the anode and cathode from the thyristor (how big the current is in fact based on how big the load and how big Ea), therefore the thyristor is entirely excited. This conduction process is finished in an exceedingly limited time.
2. After the thyristor is excited, its conductive state will be maintained by the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it is actually still inside the conductive state. Therefore, the purpose of the control electrode is only to trigger the thyristor to change on. When the thyristor is excited, the control electrode loses its function.
3. The only way to switch off the turned-on thyristor is always to reduce the anode current so that it is insufficient to keep up the positive feedback process. How you can reduce the anode current is always to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep the thyristor inside the conducting state is referred to as the holding current from the thyristor. Therefore, as it happens, as long as the anode current is less than the holding current, the thyristor could be switched off.

What exactly is the difference between a transistor along with a thyristor?

Structure

Transistors usually contain 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.

Functioning conditions:

The task of any transistor relies upon electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor demands a forward voltage along with a trigger current at the gate to change on or off.

Application areas

Transistors are commonly used in amplification, switches, oscillators, as well as other facets of electronic circuits.

Thyristors are mainly utilized in electronic circuits like 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 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 related to stability and reliability and often have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors may be used in similar applications in some instances, because of their different structures and operating principles, they have noticeable variations in performance and make use of occasions.

Application scope of thyristor

• In power electronic equipment, thyristors may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors may be used in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors may be used to control the current flow for 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 really is one from the leading enterprises in the Home Accessory & Solar Power System, which can be fully involved in the development of power industry, intelligent operation and maintenance handling 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.