Just what is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure contains 4 quantities of semiconductor materials, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles are the critical parts in 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, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of the Thyristor is generally 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 in the thyristor is the fact 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 used in between the anode and cathode (the anode is linked to the favorable pole in the power supply, and the cathode is attached to the negative pole in the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and 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, as well as a forward voltage is applied to the control electrode (referred to as a trigger, and 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 excited, whether or not the voltage around the control electrode is taken away (that is, K is excited again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At the moment, 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 applied to the control electrode, a reverse voltage is applied in between the anode and cathode, and 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) When the thyristor is exposed to a reverse anode voltage, the thyristor is within a reverse blocking state no matter what voltage the gate is exposed to.

2) When the thyristor is exposed to a forward anode voltage, the thyristor is only going to conduct when the gate is exposed to a forward voltage. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) When the thyristor is excited, provided that you will find a specific forward anode voltage, the thyristor will stay excited no matter the gate voltage. Which is, after the thyristor is excited, 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 problem for the thyristor to conduct is the fact a forward voltage needs to be applied in between the anode and the cathode, as well as an appropriate forward voltage ought to be applied in between the gate and the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode must be shut down, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is actually a unique triode made from three PN junctions. It may be equivalently viewed as comprising a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is applied in between the anode and cathode in the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still switched off because BG1 has no base current. In case a forward voltage is applied to 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 brought in the collector of BG2. This current is brought to BG1 for amplification and then brought to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A big current appears inside the emitters of the two transistors, that is, the anode and cathode in the thyristor (how big the current is really determined by how big the stress and how big Ea), so the thyristor is entirely excited. This conduction process is finished in a really short period of time.
2. Following the thyristor is excited, its conductive state will be maintained from the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is still inside the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to transform on. After the thyristor is excited, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor is always to reduce the anode current so that it is inadequate to keep up the positive feedback process. The best way to reduce the anode current is always to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current required to maintain the thyristor inside the conducting state is known as the holding current in the thyristor. Therefore, as it happens, provided that the anode current is lower than the holding current, the thyristor can be switched off.

Exactly what is the distinction between a transistor as well as 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.

Working conditions:

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

The thyristor demands a forward voltage as well as a trigger current in the gate to transform on or off.

Application areas

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

Thyristors are mainly utilized 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 achieve current amplification.

The thyristor is excited or off by managing the trigger voltage in the control electrode to comprehend the switching function.

Circuit parameters

The circuit parameters of thyristors are related to 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 sometimes, because of the different structures and working principles, they have got noticeable variations in performance and utilize occasions.

Application scope of thyristor

• In power electronic equipment, thyristors may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors may be used in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors may be used to control the current flow to 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 in the leading enterprises in the Home Accessory & Solar Power System, that is fully active in the progression of power industry, intelligent operation and maintenance control over power plants, solar power 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.