Just what is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains four levels of semiconductor materials, including 3 PN junctions corresponding to 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 various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the silicon-controlled rectifier is normally represented through 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 functioning condition of the thyristor is that each time 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 in between the anode and cathode (the anode is linked to the favorable pole of the power supply, and the cathode is attached to the negative pole of the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), and the indicator light will not glow. This shows 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 used to the control electrode (known as a trigger, and the applied voltage is called trigger voltage), the indicator light turns on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, even if the voltage in the control electrode is taken away (which is, K is turned on again), the indicator light still glows. This shows that the thyristor can continue to conduct. Currently, in order to shut down the conductive thyristor, the power supply Ea has to be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used to the control electrode, a reverse voltage is used in between the anode and cathode, and the indicator light will not glow at this time. This shows that the thyristor is not conducting and will reverse blocking.

5. In summary

1) If the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state regardless of what voltage the gate is put through.

2) If the thyristor is put through a forward anode voltage, the thyristor will only conduct if the gate is put through a forward voltage. Currently, the thyristor is in the forward conduction state, which is the thyristor characteristic, which is, the controllable characteristic.

3) If the thyristor is turned on, provided that you will find a specific forward anode voltage, the thyristor will remain turned on whatever the gate voltage. Which is, following the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

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

5) The disorder for your thyristor to conduct is that a forward voltage should 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 has to be shut down, 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 could be equivalently regarded as composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is used in between the anode and cathode of the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains turned off because BG1 has no base current. In case a forward voltage is used to 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 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 delivered to BG1 for amplification and after that delivered 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 large current appears inside the emitters of the two transistors, which is, the anode and cathode of the thyristor (the size of the current is really dependant on the size of the load and the size of Ea), and so the thyristor is entirely turned on. This conduction process is finished in a really short time.
2. After the thyristor is turned on, its conductive state will be maintained through the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it really is still inside the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to transform on. Once the thyristor is turned on, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor is always to decrease the anode current so that it is inadequate to keep up 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 required to maintain the thyristor inside the conducting state is called the holding current of the thyristor. Therefore, strictly speaking, provided that the anode current is under the holding current, the thyristor may be turned off.

What exactly is the distinction between a transistor and a thyristor?

Structure

Transistors usually contain 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.

Functioning conditions:

The job of the 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 on the gate to transform on or off.

Application areas

Transistors are widely used 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.

Method 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 controlling the trigger voltage of the control electrode to realize 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 can be utilized in similar applications in some cases, due to their different structures and functioning principles, they may have noticeable differences in performance and make use of 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 light control devices.
• In induction cookers and electric water heaters, thyristors could be used to control the current flow to the heating element.
• In electric vehicles, transistors can be utilized 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, that is fully involved in the development of power industry, intelligent operation and maintenance management of power plants, solar power 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.