What exactly is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes four quantities of semiconductor components, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles would be 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 working status. Therefore, thyristors are popular in various electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a Thyristor is usually represented through 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 working 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 utilized involving the anode and cathode (the anode is linked to the favorable pole from the power supply, as well as the cathode is attached to the negative pole from the power supply). But no forward voltage is applied for the control pole (i.e., K is disconnected), as well as the indicator light does not light up. This implies that the thyristor is not conducting and contains 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 (known as a trigger, as well as the applied voltage is known as trigger voltage), the indicator light switches on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after the thyristor is turned on, even if the voltage on the control electrode is taken away (which is, K is turned on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At the moment, to be able to stop the conductive thyristor, the power supply Ea has to be stop 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, as well as the indicator light does not light up at this time. This implies that the thyristor is not conducting and can reverse blocking.

5. To sum up

1) If the thyristor is put through a reverse anode voltage, the thyristor is within a reverse blocking state whatever voltage the gate is put through.

2) If the thyristor is put through a forward anode voltage, the thyristor will simply conduct if the gate is put through a forward voltage. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) If the thyristor is turned on, as long as there is a specific forward anode voltage, the thyristor will stay turned on no matter the gate voltage. That is, after the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

4) If the thyristor is on, as well as the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.

5) The problem for that thyristor to conduct is that a forward voltage should be applied involving the anode as well as the cathode, as well as an appropriate forward voltage should also be applied involving the gate as well as the cathode. To transform off a conducting thyristor, the forward voltage involving the anode and cathode has to be stop, or even the voltage has to be reversed.

Working principle of thyristor

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

1. If a forward voltage is applied 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 turned off because BG1 has no base current. If 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, 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 will be introduced the collector of BG2. This current is brought to BG1 for amplification and then brought 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 in the emitters of the two transistors, which is, the anode and cathode from the thyristor (the size of the current is in fact dependant on the size of the stress and the size of Ea), therefore 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 will be maintained through the positive feedback effect from the tube itself. Even if the forward voltage from the control electrode disappears, it really is still in the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. When the thyristor is turned on, the control electrode loses its function.
3. The best way to turn off the turned-on thyristor is always to decrease the anode current so that it is not enough to keep the positive feedback process. How you can decrease the anode current is always to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep your thyristor in the conducting state is known as the holding current from the thyristor. Therefore, as it happens, as long as the anode current is lower than the holding current, the thyristor can be turned off.

Exactly what is the difference between a transistor and a thyristor?

Structure

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

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

Operating conditions:

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

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

Application areas

Transistors are popular in amplification, switches, oscillators, along with other facets of electronic circuits.

Thyristors are mainly 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 from the control electrode to understand the switching function.

Circuit parameters

The circuit parameters of thyristors are based on stability and reliability and usually have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors may be used in similar applications in some cases, due to their different structures and working 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.
• Inside the lighting field, thyristors may be used 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 may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is one from the leading enterprises in the Home Accessory & Solar Power System, which is 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 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.