Just what is a thyristor?
A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four levels of semiconductor elements, including 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles are 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 working status. Therefore, thyristors are widely used in different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.
The graphical symbol of a semiconductor device is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The working condition from the thyristor is that whenever 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 involving the anode and cathode (the anode is connected to the favorable pole from the power supply, and the cathode is attached to the negative pole from the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), and the indicator light does not light up. This implies that the thyristor is not conducting and contains forward blocking capability.
- Controllable conduction
As shown in Figure b above, when K is closed, as well as a forward voltage is used for the control electrode (called a trigger, and the applied voltage is known as trigger voltage), the indicator light turns on. Because of this the transistor can control conduction.
- Continuous conduction
As shown in Figure c above, following the thyristor is excited, even when the voltage in the control electrode is removed (that is, K is excited again), the indicator light still glows. This implies that the thyristor can still conduct. At the moment, to be able to shut down the conductive thyristor, the power supply Ea has to be shut down or reversed.
- Reverse blocking
As shown in Figure d above, although a forward voltage is used for the control electrode, a reverse voltage is used involving the anode and cathode, and the indicator light does not light up currently. This implies that the thyristor is not conducting and will reverse blocking.
- In conclusion
1) When the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state whatever voltage the gate is put through.
2) When the thyristor is put through a forward anode voltage, the thyristor will only conduct when the gate is put through a forward voltage. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, that is, the controllable characteristic.
3) When the thyristor is excited, so long as you will find a specific forward anode voltage, the thyristor will stay excited regardless of the gate voltage. Which is, following the thyristor is excited, the gate will lose its function. The gate only works as a trigger.
4) When the thyristor is on, and the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.
5) The condition for the thyristor to conduct is that a forward voltage needs to be applied involving the anode and the cathode, and an appropriate forward voltage also need to be applied involving the gate and the cathode. To transform off a conducting thyristor, the forward voltage involving the anode and cathode has to be shut down, or the voltage has to be reversed.
Working principle of thyristor
A thyristor is essentially an exclusive triode composed of three PN junctions. It could be equivalently regarded as comprising a PNP transistor (BG2) and an NPN transistor (BG1).
- If a forward voltage is used involving the anode and cathode from the thyristor without applying a forward voltage for the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still switched off because BG1 has no base current. If a forward voltage is used for the control electrode currently, BG1 is triggered to produce a base 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 is going to be introduced the collector of BG2. This current is brought to BG1 for amplification then brought to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A sizable current appears in the emitters of these two transistors, that is, the anode and cathode from the thyristor (the dimensions of the current is in fact determined by the dimensions of the burden and the dimensions of Ea), so the thyristor is entirely excited. This conduction process is done in a very limited time.
- Right after the thyristor is excited, 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 actually still in the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to change on. After the thyristor is excited, the control electrode loses its function.
- The best way to shut off the turned-on thyristor is always to decrease the anode current that it is inadequate to maintain the positive feedback process. The best way to decrease the anode current is always to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current required to keep the thyristor in the conducting state is known as the holding current from the thyristor. Therefore, as it happens, so long as the anode current is under the holding current, the thyristor could be switched off.
What is the distinction between a transistor as well as a thyristor?
Transistors usually include 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.
The work of a transistor depends on electrical signals to control its opening and closing, allowing fast switching operations.
The thyristor needs a forward voltage as well as a trigger current in the gate to change on or off.
Transistors are widely used in amplification, switches, oscillators, and other facets of electronic circuits.
Thyristors are mostly found in electronic circuits including 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 attain current amplification.
The thyristor is excited or off by manipulating the trigger voltage from the control electrode to comprehend 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 in some cases, because of their different structures and working principles, they may have noticeable variations in performance and utilize 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 light control devices.
- In induction cookers and electric water heaters, thyristors may be used to control the current flow for the heating element.
- In electric vehicles, transistors can be used in motor controllers.
PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It really is one from the leading enterprises in the Home Accessory & Solar Power System, which can be fully involved in the development of power industry, intelligent operation and maintenance management of power plants, solar power 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.