So what is a thyristor?
A thyristor is really a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains 4 levels of semiconductor materials, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles would be the critical parts of 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 widely 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 semiconductor device is usually represented from 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 working condition of the thyristor is the fact that when a forward voltage is used, the gate should have a trigger current.
Characteristics of thyristor
- Forward blocking
As shown in Figure a above, when an ahead voltage is utilized between the anode and cathode (the anode is connected to the favorable pole of the power supply, and also the cathode is linked to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light fails to glow. This implies that the thyristor is not really conducting and it has forward blocking capability.
- Controllable conduction
As shown in Figure b above, when K is closed, along with a forward voltage is used towards the control electrode (called a trigger, and also the applied voltage is known as trigger voltage), the indicator light turns on. Which means that the transistor can control conduction.
- Continuous conduction
As shown in Figure c above, after the thyristor is switched on, whether or not the voltage around the control electrode is taken away (that is certainly, K is switched on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At the moment, in order to stop the conductive thyristor, the power supply Ea must be stop or reversed.
- Reverse blocking
As shown in Figure d above, although a forward voltage is used towards the control electrode, a reverse voltage is used between the anode and cathode, and also the indicator light fails to glow at the moment. This implies that the thyristor is not really conducting and may reverse blocking.
- In summary
1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is at a reverse blocking state regardless of what voltage the gate is subjected to.
2) Once the thyristor is subjected to a forward anode voltage, the thyristor will simply conduct when the gate is subjected to a forward voltage. At the moment, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.
3) Once the thyristor is switched on, provided that there exists a specific forward anode voltage, the thyristor will always be switched on no matter the gate voltage. That is certainly, after the thyristor is switched on, the gate will lose its function. The gate only works as a trigger.
4) Once the thyristor is on, and also the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.
5) The problem for your thyristor to conduct is the fact that a forward voltage ought to be applied between the anode and also the cathode, plus an appropriate forward voltage ought to be applied between the gate and also 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 essentially a unique triode composed of three PN junctions. It could be equivalently regarded as comprising a PNP transistor (BG2) plus an NPN transistor (BG1).
- If a forward voltage is used between the anode and cathode of the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains turned off because BG1 has no base current. If a forward voltage is used towards the control electrode at the moment, BG1 is triggered to generate basics current Ig. BG1 amplifies this current, along with a ß1Ig current is obtained in its 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 get in a saturated conduction state quickly. A sizable current appears inside the emitters of these two transistors, that is certainly, the anode and cathode of the thyristor (the dimensions of the current is really based on the dimensions of the burden and the dimensions of Ea), so the thyristor is completely switched on. This conduction process is completed in a really short time.
- Following the thyristor is switched on, its conductive state will likely be maintained from the positive feedback effect of the tube itself. Even when the forward voltage of the control electrode disappears, it really is still inside the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to transform on. Once the thyristor is switched on, the control electrode loses its function.
- The best way to shut off the turned-on thyristor would be to reduce the anode current that it is inadequate to keep up the positive feedback process. How you can reduce the anode current would be to stop the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to keep your thyristor inside the conducting state is known as the holding current of the thyristor. Therefore, strictly speaking, provided that the anode current is less than the holding current, the thyristor can be turned off.
What exactly is the difference between a transistor along with a thyristor?
Transistors usually contain a PNP or NPN structure composed of three semiconductor materials.
The thyristor is made up of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.
The job of the 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 transform on or off.
Transistors are widely used in amplification, switches, oscillators, along with other elements of electronic circuits.
Thyristors are mostly utilized 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 switched on or off by controlling the trigger voltage of the control electrode to realize 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 summarize, although transistors and thyristors may be used in similar applications in some cases, due to their different structures and working principles, they have 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 towards the heating element.
- In electric vehicles, transistors may be used in motor controllers.
PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It really is one of the leading enterprises in the Home Accessory & Solar Power System, which is fully working in the growth and development of power industry, intelligent operation and maintenance management of power plants, solar panel and related solar products manufacturing.
It accepts payment via Charge 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.