What is a thyristor?
A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure contains four quantities of semiconductor materials, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles are definitely 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 functioning status. Therefore, thyristors are popular in various electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.
The graphical symbol of any Thyristor is usually 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 functioning condition from the thyristor is the fact each time a forward voltage is applied, the gate needs to have a trigger current.
Characteristics of thyristor
- Forward blocking
As shown in Figure a above, when an ahead voltage is utilized in between the anode and cathode (the anode is linked to the favorable pole from the power supply, and also the cathode is connected to the negative pole from the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), and also the indicator light does not glow. This implies that the thyristor is not really conducting and has forward blocking capability.
- 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 switches on. Because of this the transistor can control conduction.
- Continuous conduction
As shown in Figure c above, right after the thyristor is excited, even if the voltage on the control electrode is taken off (that is, K is excited again), the indicator light still glows. This implies that the thyristor can still conduct. At this time, in order to shut down the conductive thyristor, the power supply Ea should be shut down or reversed.
- Reverse blocking
As shown in Figure d above, although a forward voltage is applied towards the control electrode, a reverse voltage is applied in between the anode and cathode, and also the indicator light does not glow at the moment. This implies that the thyristor is not really conducting and will reverse blocking.
- To sum up
1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is within a reverse blocking state whatever voltage the gate is subjected to.
2) Once the thyristor is subjected to a forward anode voltage, the thyristor will only conduct when the gate is subjected to a forward voltage. At this time, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.
3) Once the thyristor is excited, as long as there is a specific forward anode voltage, the thyristor will stay excited no matter the gate voltage. Which is, right after the thyristor is excited, 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 your thyristor to conduct is the fact a forward voltage needs to be applied in between the anode and also the cathode, as well as an appropriate forward voltage ought to be applied in between the gate and also the cathode. To turn off a conducting thyristor, the forward voltage in between the anode and cathode should be shut down, or the voltage should be reversed.
Working principle of thyristor
A thyristor is essentially a unique triode made up of three PN junctions. It could be equivalently viewed as composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).
- When a forward voltage is applied in between the anode and cathode from the thyristor without applying a forward voltage towards 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. When a forward voltage is applied towards the control electrode at the moment, BG1 is triggered to create basics 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 likely be brought in the collector of BG2. This current is sent to BG1 for amplification then sent to BG2 for amplification again. Such repeated amplification forms a crucial positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A sizable current appears within the emitters of the two transistors, that is, the anode and cathode from the thyristor (how big the current is in fact determined by how big the load and how big Ea), therefore the thyristor is completely excited. This conduction process is done in a very limited time.
- After the thyristor is excited, its conductive state will likely be maintained through the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it is actually still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. After the thyristor is excited, the control electrode loses its function.
- The only way to turn off the turned-on thyristor is to decrease the anode current so that it is insufficient to keep the positive feedback process. The best way to decrease the anode current is to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current needed to keep the thyristor within the conducting state is known 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 may be switched off.
What is the distinction between a transistor as well as a thyristor?
Transistors usually consist of 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.
The work of any transistor relies 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 on the gate to change on or off.
Transistors are popular in amplification, switches, oscillators, as well as other aspects of electronic circuits.
Thyristors are mostly utilized in electronic circuits including 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 accomplish current amplification.
The thyristor is excited or off by managing the trigger voltage from the control electrode to understand the switching function.
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 sum up, although transistors and thyristors can be utilized in similar applications in some cases, because of the different structures and functioning principles, they have got noticeable variations in performance and utilize 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 towards the heating element.
- In electric vehicles, transistors can be utilized in motor controllers.
PDDN Photoelectron Technology Co., Ltd is a wonderful 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 management of power plants, solar panel 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.