So what is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes 4 quantities of semiconductor components, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles are definitely the critical parts of 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 commonly used in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the semiconductor device is usually represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The working condition of the thyristor is the fact that each time 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 can be used between the anode and cathode (the anode is attached 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 towards the control pole (i.e., K is disconnected), and also the indicator light fails to light up. This demonstrates that the thyristor is not really conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is applied towards the control electrode (called a trigger, and also the applied voltage is known as trigger voltage), the indicator light turns on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, right after the thyristor is switched on, whether or not the voltage around the control electrode is taken away (that is, K is switched on again), the indicator light still glows. This demonstrates that the thyristor can carry on and conduct. Currently, 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 applied towards the control electrode, a reverse voltage is applied between the anode and cathode, and also the indicator light fails to light up at this time. This demonstrates that the thyristor is not really conducting and will reverse blocking.

5. To sum up

1) Once 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) Once 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. Currently, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.

3) Once the thyristor is switched on, as long as you will find a specific forward anode voltage, the thyristor will always be switched on no matter the gate voltage. Which is, right after the thyristor is switched on, the gate will lose its function. The gate only serves 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 the fact that a forward voltage needs to be applied between the anode and also the cathode, and an appropriate forward voltage ought to be applied between the gate and also the cathode. To change 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 actually a unique triode made up of three PN junctions. It could be equivalently thought to be composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. If a forward voltage is applied between the anode and cathode of the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains turned off because BG1 has no base current. If a forward voltage is applied towards the control electrode at this time, BG1 is triggered to create basics current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in the 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 and after that delivered 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 inside the emitters of these two transistors, that is, the anode and cathode of the thyristor (how big the current is in fact dependant on how big the stress and how big Ea), and so the thyristor is entirely switched on. This conduction process is completed in a really short period of time.
2. Right after the thyristor is switched on, its conductive state will be maintained from the positive feedback effect of the tube itself. Even when the forward voltage of 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 transform on. After the thyristor is switched on, the control electrode loses its function.
3. The only way to switch off the turned-on thyristor is always to lessen the anode current that it is inadequate to keep up the positive feedback process. The way to lessen the anode current is always to cut off 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, as it happens, as long as the anode current is less than the holding current, the thyristor may be turned off.

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

Structure

Transistors usually include 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 the transistor depends on electrical signals to control its opening and closing, allowing fast switching operations.

The thyristor requires a forward voltage as well as a trigger current at the gate to transform 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.

Method of working

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

The thyristor is switched 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 often have higher turn-off voltage and larger on-current.

To sum up, although transistors and thyristors may be used in similar applications sometimes, because of their different structures and working principles, they have noticeable differences 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 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 may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a wonderful thyristor supplier. It is one of the leading enterprises in the Home Accessory & Solar Power System, which is fully active in the development of power industry, intelligent operation and maintenance management of power plants, solar panel and related solar products manufacturing.

It accepts payment via Credit 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.