What exactly is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of four levels of semiconductor materials, 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 functioning status. Therefore, thyristors are commonly used in a variety of electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of any Thyristor is normally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also have 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 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 utilized involving the anode and cathode (the anode is linked to the favorable pole from the power supply, and the cathode is connected 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 will not glow. This demonstrates that the thyristor is not really conducting and has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is used for the control electrode (called a trigger, and the applied voltage is referred to 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, following the thyristor is switched on, even if the voltage in the control electrode is removed (which is, K is switched on again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. At this time, in order to shut down the conductive thyristor, the power supply Ea must be shut down 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 involving the anode and cathode, and the indicator light will not glow at this time. This demonstrates that the thyristor is not really conducting and may reverse blocking.

5. In summary

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

2) When the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct when the gate is subjected to a forward voltage. At this time, the thyristor is within the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) When the thyristor is switched on, so long as you will find a specific forward anode voltage, the thyristor will always be switched on whatever the gate voltage. Which is, following the thyristor is switched on, the gate will lose its function. The gate only serves as a trigger.

4) When the thyristor is on, and the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

5) The disorder for that thyristor to conduct is that a forward voltage should be applied involving the anode and the cathode, as well as an appropriate forward voltage ought to be applied involving the gate and the cathode. To transform off a conducting thyristor, the forward voltage involving the anode and cathode must be shut down, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is basically a distinctive triode made up of three PN junctions. It may be equivalently viewed as consisting of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is used involving 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 this time, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, as well as 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 delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A big current appears inside the emitters of these two transistors, which is, the anode and cathode from the thyristor (the size of the current is really determined by the size of the load and the size of Ea), and so the thyristor is completely switched on. This conduction process is finished in an exceedingly limited time.
2. After the thyristor is switched on, its conductive state will be maintained through the positive feedback effect from the tube itself. Whether or not the forward voltage from the control electrode disappears, it is still inside the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to change on. Once the thyristor is switched on, the control electrode loses its function.
3. The only method to turn off the turned-on thyristor is to reduce the anode current that it is inadequate to maintain the positive feedback process. The way to reduce the anode current is to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current needed to maintain the thyristor inside the conducting state is referred to as the holding current from the thyristor. Therefore, strictly speaking, so long as the anode current is under the holding current, the thyristor may be switched off.

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

Structure

Transistors usually consist of 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 work of any transistor relies upon electrical signals to control its opening and closing, allowing fast switching operations.

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

Application areas

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

Thyristors are mostly used in electronic circuits such as controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Way of working

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

The thyristor is switched on or off by manipulating 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 can be utilized in similar applications sometimes, because of their different structures and functioning principles, they have got noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be utilized in frequency converters, motor controllers, welding machines, power supplies, etc.
• In 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 for the heating element.
• In electric vehicles, transistors can be utilized 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 involved in the progression of power industry, intelligent operation and maintenance handling of power plants, solar power panel and related solar products manufacturing.

It accepts payment via Bank 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.