What is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of 4 levels of semiconductor elements, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles are 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 commonly used in different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a semiconductor device is normally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The functioning condition from the thyristor is the fact when 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 used between 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 used towards the control pole (i.e., K is disconnected), as well as the indicator light will not illuminate. This implies 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 used towards the control electrode (called a trigger, as well as the applied voltage is known as trigger voltage), the indicator light turns on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after the thyristor is turned on, even when the voltage on the control electrode is taken away (that is certainly, K is turned on again), the indicator light still glows. This implies that the thyristor can continue to conduct. At this time, to be able to cut off the conductive thyristor, the power supply Ea must be cut off or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used towards the control electrode, a reverse voltage is used between the anode and cathode, as well as the indicator light will not illuminate at this time. This implies that the thyristor will not be conducting and may reverse blocking.

5. To sum up

1) When the thyristor is subjected to a reverse anode voltage, the thyristor is at a reverse blocking state whatever voltage the gate is subjected to.

2) When the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct once the gate is subjected to a forward voltage. At this time, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) When the thyristor is turned on, as long as there exists a specific forward anode voltage, the thyristor will remain turned on whatever 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) When the thyristor is on, as well as the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.

5) The condition for the thyristor to conduct is the fact a forward voltage needs to be applied between the anode as well as the cathode, plus an appropriate forward voltage also need to be applied between the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage between the anode and cathode must be cut off, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is essentially a distinctive triode made from three PN junctions. It may be equivalently regarded as comprising a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If a forward voltage is used between the anode and cathode from the thyristor without applying a forward voltage towards 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 towards the control electrode at this time, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in the 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 brought to BG1 for amplification then brought 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 sizable current appears in the emitters of these two transistors, that is certainly, the anode and cathode from the thyristor (the size of the current is in fact dependant on the size of the burden and the size of Ea), so the thyristor is totally turned on. This conduction process is done in a really short period of time.
2. Right after the thyristor is turned on, its conductive state is going to be maintained by the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it is actually still in the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to transform on. After the thyristor is turned on, the control electrode loses its function.
3. The best way to shut off the turned-on thyristor is to decrease the anode current that it is inadequate to keep the positive feedback process. The best way to decrease the anode current is to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep your thyristor in the conducting state is known as the holding current from the thyristor. Therefore, strictly speaking, as long as the anode current is under the holding current, the thyristor could be switched off.

What is the distinction between a transistor and a thyristor?

Structure

Transistors usually contain a PNP or NPN structure made from 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 opening and closing, allowing fast switching operations.

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

Application areas

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

Thyristors are mainly utilized 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 attain current amplification.

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

Circuit parameters

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

To summarize, although transistors and thyristors can be utilized in similar applications in some cases, because of their different structures and functioning principles, they have got 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.
• In the lighting field, thyristors can be utilized in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors could be used to control the current flow towards the heating element.
• In electric vehicles, transistors can be utilized in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It really is one from the leading enterprises in the Home Accessory & Solar Power System, which is fully active in the development of power industry, intelligent operation and maintenance handling of power plants, solar 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.