Just what is a thyristor?
A thyristor is really a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure consists of 4 levels of semiconductor components, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles are 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 working status. Therefore, thyristors are popular in various electronic circuits, like 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”). Furthermore, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The working condition from the thyristor is that when a forward voltage is used, the gate will need 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, as well as the cathode is connected to the negative pole from 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 demonstrates that the thyristor is not really conducting and has forward blocking capability.
- Controllable conduction
As shown in Figure b above, when K is closed, and a forward voltage is used to the control electrode (known as a trigger, as well as the applied voltage is called trigger voltage), the indicator light switches on. Because of this the transistor can control conduction.
- Continuous conduction
As shown in Figure c above, following the thyristor is turned on, whether or not the voltage around the control electrode is removed (that is certainly, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can carry on and conduct. At this time, so that you can cut off the conductive thyristor, the power supply Ea has to be cut off or reversed.
- 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 demonstrates that the thyristor is not really conducting and will reverse blocking.
- To sum up
1) Once the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state regardless of what voltage the gate is put through.
2) Once the thyristor is put through a forward anode voltage, the thyristor will simply conduct once the gate is put through a forward voltage. At this time, the thyristor is within the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.
3) Once the thyristor is turned on, as long as you will find a specific forward anode voltage, the thyristor will remain turned on no matter the gate voltage. That is certainly, following the thyristor is turned on, the gate will lose its function. The gate only works as a trigger.
4) Once 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 your thyristor to conduct is that a forward voltage should be applied in between the anode as well as the cathode, and an appropriate forward voltage ought to be applied in between the gate as well as the cathode. To transform off a conducting thyristor, the forward voltage in between the anode and cathode has to be cut off, or the voltage has to be reversed.
Working principle of thyristor
A thyristor is basically an exclusive triode composed of three PN junctions. It could be equivalently viewed as comprising a PNP transistor (BG2) and an NPN transistor (BG1).
- If a forward voltage is used in 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 is still turned off because BG1 has no base current. If a forward voltage is used to the control electrode currently, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, and 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 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 large current appears inside the emitters of the two transistors, that is certainly, the anode and cathode from the thyristor (the dimensions of the current is really based on the dimensions of the burden and the dimensions of Ea), and so the thyristor is totally turned on. This conduction process is completed in an exceedingly short time.
- Right after the thyristor is turned on, its conductive state will be maintained from the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it really is still inside the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to transform on. After the thyristor is turned on, the control electrode loses its function.
- The best way to switch off the turned-on thyristor is always to decrease the anode current that it is insufficient to maintain the positive feedback process. How you can decrease the anode current is always to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current required to keep your thyristor inside the conducting state is called 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 turned off.
What exactly is the distinction between a transistor and a thyristor?
Transistors usually consist of 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 task of the transistor depends on electrical signals to control its opening and closing, allowing fast switching operations.
The thyristor demands a forward voltage and a trigger current on the gate to transform on or off.
Transistors are popular in amplification, switches, oscillators, along with other aspects of electronic circuits.
Thyristors are mostly found in electronic circuits like 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 attain current amplification.
The thyristor is turned on or off by controlling the trigger voltage from the control electrode to understand the switching function.
The circuit parameters of thyristors are related to 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 sometimes, due to their different structures and working principles, they have noticeable variations 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.
- In 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 to 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 one from the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the development of power industry, intelligent operation and maintenance handling of power plants, solar power 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.