So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure consists of four quantities of semiconductor materials, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles are the critical parts of 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 widely used in different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a silicon-controlled rectifier is normally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The functioning condition of the thyristor is that when a forward voltage is applied, 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 of the power supply, and also the cathode is attached to the negative pole of 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 light up. This shows 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, along with a forward voltage is applied for the control electrode (called a trigger, and also the applied voltage is known 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, right after the thyristor is turned on, even if the voltage on the control electrode is taken away (that is, K is turned on again), the indicator light still glows. This shows that the thyristor can continue to conduct. Currently, to be able 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 applied for the control electrode, a reverse voltage is applied involving the anode and cathode, and also the indicator light fails to light up at this time. This shows that the thyristor is not really conducting and will reverse blocking.

5. In summary

1) Once 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) Once the thyristor is exposed to a forward anode voltage, the thyristor is only going to conduct if the gate is exposed to a forward voltage. Currently, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) Once the thyristor is turned on, provided that there is a specific forward anode voltage, the thyristor will remain turned on no matter the gate voltage. That 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 seal to zero, the thyristor turns off.

5) The disorder for the thyristor to conduct is that a forward voltage ought to be applied involving the anode and also the cathode, and an appropriate forward voltage ought to be applied involving the gate and also 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 actually a distinctive triode made up of three PN junctions. It may be equivalently thought to be consisting of a PNP transistor (BG2) and an NPN transistor (BG1).

1. When a forward voltage is applied involving the anode and cathode of 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. When a forward voltage is applied for the control electrode at this time, BG1 is triggered to generate a base 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 likely be brought in the collector of BG2. This current is delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A big current appears inside the emitters of the two transistors, that is, the anode and cathode of the thyristor (the dimensions of the current is in fact based on the dimensions of the burden and the dimensions of Ea), so the thyristor is totally turned on. This conduction process is done in a really short period of time.
2. After the thyristor is turned on, its conductive state will likely be maintained from the positive feedback effect of the tube itself. Even when the forward voltage of the control electrode disappears, it is actually still inside the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. Once the thyristor is turned on, the control electrode loses its function.
3. The only way to turn off the turned-on thyristor is always to decrease the anode current that it is inadequate to maintain the positive feedback process. How you can decrease the anode current is always to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current needed to maintain the thyristor inside the conducting state is known as the holding current of the thyristor. Therefore, strictly speaking, provided that the anode current is less than the holding current, the thyristor may be switched off.

Exactly what is the distinction between a transistor along with 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.

Operating conditions:

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

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

Application areas

Transistors are widely used in amplification, switches, oscillators, along with other aspects of electronic circuits.

Thyristors are mostly found in electronic circuits including 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 achieve current amplification.

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

Circuit parameters

The circuit parameters of thyristors are related to stability and reliability and in most cases have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors may be used in similar applications sometimes, because of the different structures and functioning principles, they have got 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.
• Inside 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 a wonderful thyristor supplier. It is actually one of the leading enterprises in the Home Accessory & Solar Power System, that is fully active 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. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.