What exactly 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 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, 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 functioning 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 any silicon-controlled rectifier is usually represented through 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-weight-controlled thyristors. The functioning condition from the thyristor is 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 in between the anode and cathode (the anode is linked 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 fails to glow. This demonstrates that the thyristor will not be conducting and 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 (referred to as a trigger, and also the applied voltage is called 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 turned on, even when the voltage around the control electrode is taken away (that is certainly, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can still conduct. At this time, in order to 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 applied for the control electrode, a reverse voltage is applied in between the anode and cathode, and also the indicator light fails to glow at the moment. This demonstrates that the thyristor will not be conducting and may reverse blocking.

5. To sum up

1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is in a reverse blocking state no matter what voltage the gate is subjected to.

2) Once the thyristor is subjected to a forward anode voltage, the thyristor will simply conduct once the gate is subjected to a forward voltage. At this time, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) Once the thyristor is turned on, provided that there is a specific forward anode voltage, the thyristor will always be turned on no matter the gate voltage. Which is, right after the thyristor is turned on, the gate will lose its function. The gate only functions 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 that a forward voltage ought to be applied in between the anode and also the cathode, and an appropriate forward voltage should also 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 has to be shut down, or perhaps the voltage has to be reversed.

Working principle of thyristor

A thyristor is actually an exclusive triode made from three PN junctions. It could be equivalently viewed as consisting of a PNP transistor (BG2) and an NPN transistor (BG1).

1. In case a forward voltage is applied 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 remains turned off because BG1 has no base current. In case a forward voltage is applied for the control electrode at the moment, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in its 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 and then sent to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A sizable current appears within the emitters of these two transistors, that is certainly, the anode and cathode from the thyristor (the size of the current is really based on the size of the stress and the size of Ea), so the thyristor is totally turned on. This conduction process is completed in a really limited time.
2. Following the thyristor is turned on, its conductive state is going to be maintained through the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it really is still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to turn on. Once the thyristor is turned on, the control electrode loses its function.
3. The only method to shut off the turned-on thyristor is to reduce the anode current that it is inadequate to keep the positive feedback process. How you can reduce the anode current is to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to keep the thyristor within the conducting state is called the holding current from the thyristor. Therefore, strictly speaking, provided that the anode current is under the holding current, the thyristor may be turned off.

What exactly is the difference between a transistor and a thyristor?

Structure

Transistors usually include 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.

Operating conditions:

The job of any 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 at 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 accomplish current amplification.

The thyristor is turned on or off by managing the trigger voltage from the control electrode to understand the switching function.

Circuit parameters

The circuit parameters of thyristors are based on 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 the different structures and functioning principles, they may have noticeable variations 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.
• Within 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 for the heating element.
• In electric vehicles, transistors may 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 active in the development 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.