Specifically what is a thyristor?
A thyristor is really a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of 4 quantities 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 various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.
The graphical symbol of the Thyristor is generally represented through 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 operating condition in the thyristor is that each time 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 can be used in between the anode and cathode (the anode is linked to the favorable pole in the power supply, and also the cathode is linked to the negative pole in the power supply). But no forward voltage is used to 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 to the control electrode (referred to as a trigger, and also the applied voltage is called trigger voltage), the indicator light switches on. Which means that the transistor can control conduction.
- Continuous conduction
As shown in Figure c above, following the thyristor is turned on, whether or not the voltage in the control electrode is taken away (that is certainly, K is turned on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At this time, to be able to 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, and also the indicator light fails to glow at the moment. This implies that the thyristor is not really conducting and can reverse blocking.
- In summary
1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is exposed to.
2) If the thyristor is exposed to a forward anode voltage, the thyristor will simply conduct once the gate is exposed to a forward voltage. At this time, the thyristor is in the forward conduction state, the thyristor characteristic, that is certainly, the controllable characteristic.
3) If the thyristor is turned on, so long as there is a specific forward anode voltage, the thyristor will always be turned on regardless of the gate voltage. That is, following the thyristor is turned on, the gate will lose its function. The gate only functions as a trigger.
4) If the thyristor is on, and also the primary circuit voltage (or current) decreases to seal to zero, the thyristor turns off.
5) The disorder for that thyristor to conduct is that a forward voltage needs to be applied in between the anode and also the cathode, plus an appropriate forward voltage should also be applied in between the gate and also the cathode. To turn off a conducting thyristor, the forward voltage in between the anode and cathode has to be cut off, or even the voltage has to be reversed.
Working principle of thyristor
A thyristor is essentially a unique triode made from three PN junctions. It can be equivalently regarded as consisting of a PNP transistor (BG2) plus an NPN transistor (BG1).
- If a forward voltage is used in 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 is still turned off because BG1 has no base current. If a forward voltage is used to the control electrode at the moment, BG1 is triggered to produce 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 is going to be introduced the collector of BG2. This current is sent to BG1 for amplification then sent 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 within the emitters of these two transistors, that is certainly, the anode and cathode in the thyristor (the dimensions of the current is in fact based on the dimensions of the burden and the dimensions of Ea), therefore the thyristor is completely turned on. This conduction process is completed in an exceedingly short time.
- Following the thyristor is turned on, its conductive state is going to be maintained through the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it really is still within the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to transform on. When the thyristor is turned on, the control electrode loses its function.
- The only method to shut off the turned-on thyristor would be to lessen the anode current that it is inadequate to keep up the positive feedback process. The best way to lessen the anode current would be to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current required to keep your thyristor within the conducting state is called the holding current in the thyristor. Therefore, as it happens, so long as 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 consist of a PNP or NPN structure made from three semiconductor materials.
The thyristor consists 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 closing and opening, allowing fast switching operations.
The thyristor demands a forward voltage along with a trigger current at the gate to transform on or off.
Transistors are popular in amplification, switches, oscillators, and other elements 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 manipulating the trigger voltage in the control electrode to understand the switching function.
The circuit parameters of thyristors are based on 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 utilized in similar applications in some instances, due to their different structures and operating principles, they have noticeable variations in performance and make use of occasions.
Application scope of thyristor
- In power electronic equipment, thyristors can be utilized in frequency converters, motor controllers, welding machines, power supplies, etc.
- Within the lighting field, thyristors can be utilized in dimmers and lightweight control devices.
- In induction cookers and electric water heaters, thyristors could be used to control the current flow to the heating element.
- In electric vehicles, transistors can be utilized in motor controllers.
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