Just what is a thyristor?

A thyristor is a high-power semiconductor device, also called a silicon-controlled rectifier. Its structure includes 4 levels of semiconductor materials, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles are definitely the critical parts of 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 commonly used in different electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of a silicon-controlled rectifier is generally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The working condition of the thyristor is that whenever a forward voltage is used, the gate needs to have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage can be used between the anode and cathode (the anode is connected to the favorable pole of the power supply, as well as the cathode is connected to the negative pole of the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), as well as the indicator light will not light up. This implies that the thyristor is not really conducting and it has forward blocking capability.

2. 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 known as trigger voltage), the indicator light switches on. Because of this the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, even when the voltage in the control electrode is taken off (which is, K is turned on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. Currently, 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 between the anode and cathode, as well as the indicator light will not light up at this time. This implies that the thyristor is not really conducting and can reverse blocking.

5. In summary

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

2) When the thyristor is exposed to a forward anode voltage, the thyristor will only conduct once the gate is exposed to a forward voltage. Currently, the thyristor is incorporated in the forward conduction state, which is the thyristor characteristic, which is, the controllable characteristic.

3) When the thyristor is turned on, as long as there is a specific forward anode voltage, the thyristor will stay turned on whatever the gate voltage. That is certainly, following the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

4) When the thyristor is on, as well as 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 should be applied between the anode as well as the cathode, plus an appropriate forward voltage ought to be applied between the gate as well as the cathode. To change off a conducting thyristor, the forward voltage between the anode and cathode must be cut off, or the voltage must be reversed.

Working principle of thyristor

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

1. When a forward voltage is used between the anode and cathode of 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. When a forward voltage is used to the control electrode at this time, BG1 is triggered to create 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 will likely be introduced the collector of BG2. This current is brought to BG1 for amplification and after that brought 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 within the emitters of these two transistors, which is, the anode and cathode of the thyristor (the size of the current is in fact dependant on the size of the stress and the size of Ea), and so the thyristor is entirely turned on. This conduction process is finished in a really limited time.
2. Right after the thyristor is turned on, its conductive state will likely be maintained through the positive feedback effect of the tube itself. Whether or not the forward voltage of the control electrode disappears, it is actually still within the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to change on. When the thyristor is turned on, the control electrode loses its function.
3. The best way to turn off the turned-on thyristor would be to reduce the anode current so that it is not enough to maintain the positive feedback process. The way to reduce the anode current would be to cut off the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to maintain the thyristor within the conducting state is known as the holding current of the thyristor. Therefore, as it happens, as long as the anode current is under the holding current, the thyristor may be switched off.

What exactly is the distinction between a transistor along with a thyristor?

Structure

Transistors usually include a PNP or NPN structure made from three semiconductor materials.

The thyristor is composed of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.

Working conditions:

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

The thyristor needs a forward voltage along with a trigger current at the gate to change on or off.

Application areas

Transistors are commonly used in amplification, switches, oscillators, along with other aspects of electronic circuits.

Thyristors are mostly 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 attain current amplification.

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

Circuit parameters

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 may be used in similar applications in some cases, because of their different structures and working principles, they have got noticeable variations in performance and make use of occasions.

Application scope of thyristor

• In power electronic equipment, thyristors may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors may be used in dimmers and light-weight 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 may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is an excellent thyristor supplier. It is actually one of 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 control over power plants, solar 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.