Just what is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes 4 levels of semiconductor components, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles would be 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 operating status. Therefore, thyristors are commonly used in various electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any Thyristor is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The operating condition from 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 linked to the favorable pole from the power supply, as well as the cathode is connected to the negative pole from the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), as well as the indicator light will not illuminate. This implies 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, along with a forward voltage is applied to the control electrode (called a trigger, as well as the applied voltage is referred to 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, after the thyristor is turned on, even if the voltage on the control electrode is taken off (that is, K is turned on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. Currently, so that you can stop the conductive thyristor, the power supply Ea must be stop 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 between the anode and cathode, as well as the indicator light will not illuminate at this time. This implies that the thyristor is not really conducting and can reverse blocking.

5. In summary

1) If the thyristor is put through a reverse anode voltage, the thyristor is in 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 is only going to conduct when the gate is put through a forward voltage. Currently, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.

3) If the thyristor is turned on, as long as there exists a specific forward anode voltage, the thyristor will stay turned on whatever the gate voltage. That is certainly, after the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

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

5) The problem for that thyristor to conduct is the fact that a forward voltage should be applied between the anode as well as the cathode, as well as an appropriate forward voltage also need to be applied between the gate as well as the cathode. To transform off a conducting thyristor, the forward voltage between the anode and cathode must be stop, or even the voltage must be reversed.

Working principle of thyristor

A thyristor is basically a unique triode composed of three PN junctions. It can be equivalently regarded as consisting of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is applied between the anode and cathode from the thyristor without applying a forward voltage to 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 applied to the control electrode at this time, BG1 is triggered to generate basics current Ig. BG1 amplifies this current, along with a ß1Ig current is obtained in their 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 delivered to BG1 for amplification and then delivered to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get into a saturated conduction state quickly. A big current appears inside the emitters of the two transistors, that is, the anode and cathode from the thyristor (how big the current is really dependant on how big the burden and how big Ea), so the thyristor is totally turned on. This conduction process is done in a very short period of time.
2. Following the thyristor is turned on, its conductive state is going to be maintained through the positive feedback effect from the tube itself. Whether or not the forward voltage from the control electrode disappears, it is still inside the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to change on. Once the thyristor is turned on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor is to reduce the anode current that it is not enough to maintain the positive feedback process. The way to reduce the anode current is to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep your thyristor inside the conducting state is referred to as the holding current from the thyristor. Therefore, as it happens, as long as the anode current is lower than the holding current, the thyristor can be switched off.

What exactly is the distinction between a transistor along with a thyristor?

Structure

Transistors usually consist of 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.

Operating conditions:

The work of any transistor relies upon electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor needs a forward voltage along with a trigger current on the gate to change on or off.

Application areas

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

Thyristors are mainly found in electronic circuits like controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Means of working

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

The thyristor is turned on or off by managing the trigger voltage from 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, because of the different structures and operating principles, they have got noticeable variations 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 can 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 superb thyristor supplier. It is actually one from the leading enterprises in the Home Accessory & Solar Power System, that is fully active in the development of power industry, intelligent operation and maintenance control over 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.