What is a thyristor?

A thyristor is really a high-power semiconductor device, also known as 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, 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, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any Thyristor is generally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The operating condition in the thyristor is the fact whenever a forward voltage is used, 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 in between the anode and cathode (the anode is connected to the favorable pole in the power supply, and also 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), and also the indicator light will not illuminate. This shows that the thyristor will not be conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is used to the control electrode (called a trigger, and also the applied voltage is called trigger voltage), the indicator light switches on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is excited, even when the voltage around the control electrode is taken away (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, 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 to the control electrode, a reverse voltage is used in between the anode and cathode, and also the indicator light will not illuminate at this time. This shows that the thyristor will not be conducting and may reverse blocking.

5. In conclusion

1) Once the thyristor is exposed to a reverse anode voltage, the thyristor is within a reverse blocking state no matter 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. At the moment, 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 there is a specific forward anode voltage, the thyristor will always be excited whatever the gate voltage. Which is, following the thyristor is excited, the gate will lose its function. The gate only serves as a trigger.

4) Once the thyristor is on, and also 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 also the cathode, and an appropriate forward voltage ought to be applied in between the gate and also the cathode. To transform off a conducting thyristor, the forward voltage in between the anode and cathode has to be shut down, or perhaps the voltage has to 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 in 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 this time, BG1 is triggered to produce a base current Ig. BG1 amplifies this current, as well as 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 introduced the collector of BG2. This current is sent to BG1 for amplification then sent to BG2 for amplification again. Such repeated amplification forms a crucial positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A large current appears in the emitters of these 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 burden and the size of Ea), therefore the thyristor is entirely excited. This conduction process is finished in an exceedingly limited time.
2. Right after the thyristor is excited, its conductive state is going to be maintained from the positive feedback effect in the tube itself. Even when the forward voltage in the control electrode disappears, it is actually still in the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. After the thyristor is excited, the control electrode loses its function.
3. The best way to turn off the turned-on thyristor is always to lessen the anode current so that it is insufficient to maintain the positive feedback process. The best way to lessen the anode current is always 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 called the holding current in the thyristor. Therefore, strictly speaking, provided that the anode current is lower than the holding current, the thyristor can be switched off.

What exactly is the difference between a transistor as well as a thyristor?

Structure

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

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

Working conditions:

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

The thyristor demands a forward voltage as well as a trigger current in the gate to change on or off.

Application areas

Transistors are commonly used in amplification, switches, oscillators, and 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.

Means of working

The transistor controls the collector current by holding the base current to achieve current amplification.

The thyristor is excited or off by manipulating the trigger voltage in the control electrode to comprehend 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 can be utilized in similar applications sometimes, because of the different structures and operating principles, they have noticeable variations in performance and utilize occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be utilized in frequency converters, motor controllers, welding machines, power supplies, etc.
• Inside the lighting field, thyristors can be utilized in dimmers and light-weight control devices.
• In induction cookers and electric water heaters, thyristors could be used to control the current flow to the heating element.
• In electric vehicles, transistors can be utilized 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, that is fully involved in the progression of power industry, intelligent operation and maintenance management of power plants, solar power panel 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.