Just what is a thyristor?

A thyristor is really a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes 4 quantities of semiconductor materials, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles would be 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 popular in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a semiconductor device is generally 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 light-weight-controlled thyristors. The functioning condition from the thyristor is that each time a forward voltage is used, the gate will need to have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage can be used involving the anode and cathode (the anode is attached to the favorable pole from the power supply, as well as the cathode is attached 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 does not illuminate. This demonstrates that the thyristor will not be conducting and contains forward blocking capability.

2. 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 turns on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is switched on, even when the voltage on the control electrode is removed (that is, K is switched on again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. At the moment, in order to cut off the conductive thyristor, the power supply Ea must be cut off or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used to the control electrode, a reverse voltage is used involving the anode and cathode, as well as the indicator light does not illuminate at this time. This demonstrates that the thyristor will not be conducting and may reverse blocking.

5. In conclusion

1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is at a reverse blocking state regardless of what voltage the gate is subjected to.

2) Once the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct when the gate is subjected to 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) Once the thyristor is switched on, provided that there exists a specific forward anode voltage, the thyristor will remain switched on no matter the gate voltage. That is, following the thyristor is switched 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 that thyristor to conduct is that a forward voltage needs to be applied involving the anode as well as the cathode, plus an appropriate forward voltage should also be applied involving the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode must be cut off, or perhaps the voltage must be reversed.

Working principle of thyristor

A thyristor is essentially an exclusive triode made from three PN junctions. It can be equivalently regarded as consisting of a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If a forward voltage is used involving 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 continues to be switched off because BG1 has no base current. If a forward voltage is used to the control electrode at this time, BG1 is triggered to generate a base current Ig. BG1 amplifies this current, and 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 brought to BG1 for amplification and then brought to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A large current appears in the emitters of the two transistors, that is, the anode and cathode from the thyristor (the size of the current is really based on the size of the stress and the size of Ea), and so the thyristor is entirely switched on. This conduction process is finished in a very short time.
2. Following the thyristor is switched 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 is still in the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to transform on. Once the thyristor is switched on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor is always to lessen the anode current that it is not enough to keep up the positive feedback process. The way to lessen the anode current is always to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current needed to keep your thyristor in the conducting state is called the holding current from the thyristor. Therefore, strictly speaking, provided that the anode current is lower than the holding current, the thyristor could be switched off.

What exactly is the difference between a transistor and a thyristor?

Structure

Transistors usually contain 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.

Functioning conditions:

The task of a transistor depends on electrical signals to control its closing and opening, allowing fast switching operations.

The thyristor requires a forward voltage and a trigger current at the gate to transform on or off.

Application areas

Transistors are popular in amplification, switches, oscillators, as well as other facets of electronic circuits.

Thyristors are mainly found in electronic circuits such as 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 achieve current amplification.

The thyristor is switched on or off by controlling the trigger voltage from the control electrode to understand the switching function.

Circuit parameters

The circuit parameters of thyristors are related to stability and reliability and often have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors can be used in similar applications in some cases, because of their different structures and functioning principles, they have got 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.
• Inside the lighting field, thyristors can be used in dimmers and light-weight 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 used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is actually one from the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the progression of power industry, intelligent operation and maintenance control over 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. If you are looking for high-quality thyristor, please feel free to contact us and send an inquiry.