So what is a thyristor?
A thyristor is actually a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure includes four levels of semiconductor materials, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles are definitely the critical parts in 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 operating status. Therefore, thyristors are popular in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.
The graphical symbol of the silicon-controlled rectifier is generally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The operating condition in 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 can be used between the anode and cathode (the anode is attached to the favorable pole in the power supply, as well as the cathode is connected to the negative pole in the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), as well as the indicator light does not light up. This shows that the thyristor will not be 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 to the control electrode (referred to 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, after the thyristor is turned on, whether or not the voltage on the control electrode is taken away (that is certainly, K is turned on again), the indicator light still glows. This shows that the thyristor can carry on and conduct. Currently, to be able to stop the conductive thyristor, the power supply Ea has to be stop 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 between the anode and cathode, as well as the indicator light does not light up at the moment. This shows that the thyristor will not be conducting and can reverse blocking.
- To sum up
1) When the thyristor is exposed to a reverse anode voltage, the thyristor is in a reverse blocking state no matter what voltage the gate is exposed to.
2) When the thyristor is exposed to a forward anode voltage, the thyristor will only conduct if the gate is exposed to a forward voltage. Currently, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.
3) When the thyristor is turned on, as long as there exists a specific forward anode voltage, the thyristor will always be turned on no matter the gate voltage. Which is, after the thyristor is turned on, the gate will lose its function. The gate only works as a trigger.
4) When the thyristor is on, as well as the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.
5) The disorder for the thyristor to conduct is that a forward voltage ought to be applied between the anode as well as the cathode, and an appropriate forward voltage ought to be applied between the gate as well as the cathode. To transform off a conducting thyristor, the forward voltage between the anode and cathode has to be stop, or perhaps the voltage has to be reversed.
Working principle of thyristor
A thyristor is actually an exclusive triode made from three PN junctions. It can be equivalently thought to be composed of a PNP transistor (BG2) and an NPN transistor (BG1).
- In case a forward voltage is used between the anode and cathode in the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains switched off because BG1 has no base current. In case a forward voltage is used to 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 the 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 delivered to BG1 for amplification and then delivered 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 big current appears in the emitters of these two transistors, that is certainly, the anode and cathode in the thyristor (how big the current is really dependant on how big the stress and how big Ea), and so the thyristor is totally turned on. This conduction process is finished in a really limited time.
- Following the thyristor is turned on, its conductive state is going to be maintained from the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is still in the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. After the thyristor is turned on, the control electrode loses its function.
- The only way to switch off the turned-on thyristor is always to lessen the anode current that it is insufficient to keep the positive feedback process. How you can lessen the anode current is always to stop the forward power supply Ea or reverse the bond of Ea. The minimum anode current required to maintain the thyristor in the conducting state is called the holding current in the thyristor. Therefore, strictly speaking, as long as the anode current is lower than the holding current, the thyristor can be switched off.
Exactly what is the difference between a transistor along with a thyristor?
Transistors usually consist of a PNP or NPN structure made from 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 on electrical signals to control its opening and closing, allowing fast switching operations.
The thyristor needs a forward voltage along with a trigger current in the gate to change on or off.
Transistors are popular in amplification, switches, oscillators, as well as other facets of electronic circuits.
Thyristors are mostly utilized in electronic circuits such as 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 turned on or off by controlling the trigger voltage in the control electrode to comprehend 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 used in similar applications in some cases, because of their different structures and operating principles, they 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.
- Inside the lighting field, thyristors can be used in dimmers and light control devices.
- In induction cookers and electric water heaters, thyristors can 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 superb thyristor supplier. It is one in the leading enterprises in the Home Accessory & Solar Power System, which can be fully involved in the growth and development of power industry, intelligent operation and maintenance handling of power plants, solar power panel and related solar products manufacturing.
It accepts payment via Credit 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.