Just what is a thyristor?

A thyristor is really a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure includes four quantities of semiconductor elements, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles are definitely 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 operating status. Therefore, thyristors are commonly used in a variety of electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the Thyristor is usually represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The operating condition of the thyristor is the fact whenever a forward voltage is used, the gate will need to 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 connected to the favorable pole of the power supply, as well as 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), as well as the indicator light fails to illuminate. This implies that the thyristor will not be conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is used to the control electrode (referred to as a trigger, as well as the applied voltage is called trigger voltage), the indicator light switches on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, right after the thyristor is turned on, whether or not the voltage around the control electrode is removed (which is, K is turned on again), the indicator light still glows. This implies that the thyristor can continue to conduct. At this time, so that you can 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, as well as the indicator light fails to illuminate currently. This implies that the thyristor will not be conducting and may reverse blocking.

5. In conclusion

1) When the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is put through.

2) When the thyristor is put through a forward anode voltage, the thyristor will simply conduct when the gate is put through a forward voltage. At this time, the thyristor is incorporated in the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) When the thyristor is turned on, so long as there exists a specific forward anode voltage, the thyristor will stay turned on whatever the gate voltage. That is certainly, right 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 disorder for that thyristor to conduct is the fact a forward voltage should be applied in between the anode as well as the cathode, as well as an appropriate forward voltage also need to be applied in between the gate as well as the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode has to be shut down, or perhaps the voltage has to be reversed.

Working principle of thyristor

A thyristor is essentially a distinctive triode made up of three PN junctions. It can be equivalently regarded as consisting 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 currently, BG1 is triggered to produce a base current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in their 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 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 (how big the current is in fact dependant on how big the burden and how big Ea), so the thyristor is completely turned on. This conduction process is done in a really short time.
2. After the thyristor is turned on, its conductive state will be maintained from the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it is still inside the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to change on. Once the thyristor is turned on, the control electrode loses its function.
3. The only way to turn off the turned-on thyristor would be to reduce the anode current so that it is not enough to maintain the positive feedback process. How you can reduce the anode current would be to shut down the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to keep your thyristor inside the conducting state is called the holding current of the thyristor. Therefore, strictly speaking, so long as the anode current is lower than the holding current, the thyristor may be turned off.

What exactly is the distinction 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 is composed of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.

Working conditions:

The task 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 in the gate to change on or off.

Application areas

Transistors are commonly used in amplification, switches, oscillators, as well as other elements of electronic circuits.

Thyristors are mainly found in electronic circuits including 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 achieve current amplification.

The thyristor is turned on or off by manipulating the trigger voltage of 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 sum up, although transistors and thyristors can be used in similar applications in some instances, due to their different structures and operating principles, they have got noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors can 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 to the heating element.
• In electric vehicles, transistors can be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is one of the leading enterprises in the Home Accessory & Solar Power System, which can be fully involved 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 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.