Specifically what is a thyristor?
A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of 4 quantities of semiconductor materials, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles are definitely the critical parts from 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, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.
The graphical symbol of the semiconductor device is usually represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The functioning condition from the thyristor is the fact that when a forward voltage is used, the gate needs to have a trigger current.
Characteristics of thyristor
- Forward blocking
As shown in Figure a above, when an ahead voltage can be used between the anode and cathode (the anode is connected to the favorable pole from the power supply, and the cathode is linked to the negative pole from the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and the indicator light will not light up. This shows that the thyristor is not really conducting and 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 (known as a trigger, and the applied voltage is known as trigger voltage), the indicator light turns on. This means that the transistor can control conduction.
- Continuous conduction
As shown in Figure c above, following the thyristor is turned on, even if the voltage on the control electrode is removed (that is, K is turned on again), the indicator light still glows. This shows that the thyristor can carry on and conduct. At the moment, in order to cut off the conductive thyristor, the power supply Ea must be cut off 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 the indicator light will not light up at this time. This shows that the thyristor is not really conducting and can reverse blocking.
- To sum up
1) If the thyristor is put through a reverse anode voltage, the thyristor is within a reverse blocking state whatever voltage the gate is put through.
2) If the thyristor is put through a forward anode voltage, the thyristor will simply conduct when the gate is put through a forward voltage. At the moment, the thyristor is within the forward conduction state, which is the thyristor characteristic, that is, the controllable characteristic.
3) If the thyristor is turned on, so long as there exists a specific forward anode voltage, the thyristor will remain turned on no matter 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 that thyristor to conduct is the fact that a forward voltage needs to be applied between the anode and the cathode, as well as an appropriate forward voltage also need to be applied between the gate and the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode must be cut off, or even the voltage must be reversed.
Working principle of thyristor
A thyristor is essentially an exclusive triode made up of three PN junctions. It may be equivalently thought to be composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).
- When a forward voltage is used 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 is still turned off because BG1 has no base current. When a forward voltage is used towards the control electrode at this time, BG1 is triggered to produce a base 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 is going to be brought in the collector of BG2. This current is delivered to BG1 for amplification 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 (the dimensions of the current is in fact dependant on the dimensions of the load and the dimensions of Ea), so the thyristor is totally turned on. This conduction process is done in an exceedingly limited time.
- After the thyristor is turned on, its conductive state is going to be maintained from the positive feedback effect from the tube itself. Whether or not the forward voltage from the control electrode disappears, it really 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.
- The only method to shut off the turned-on thyristor would be to decrease the anode current that it is not enough to maintain the positive feedback process. The best way to decrease the anode current would be to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current required to keep the thyristor inside the conducting state is known as the holding current from the thyristor. Therefore, as it happens, so long as the anode current is less than the holding current, the thyristor may be turned off.
What exactly is the difference between a transistor along with a thyristor?
Transistors usually consist of a PNP or NPN structure made up of three semiconductor materials.
The thyristor is made up of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.
The task of the transistor relies upon electrical signals to control its opening and closing, allowing fast switching operations.
The thyristor requires a forward voltage along with a trigger current at the gate to change on or off.
Transistors are widely used in amplification, switches, oscillators, and other facets 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 accomplish current amplification.
The thyristor is turned on or off by managing the trigger voltage from the control electrode to comprehend the switching function.
The circuit parameters of thyristors are based on stability and reliability and often have higher turn-off voltage and larger on-current.
To sum up, although transistors and thyristors can be used in similar applications sometimes, because of the different structures and functioning principles, they have got noticeable differences in performance and make use of 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 lightweight 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 can be used 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, which is fully active in the progression 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.