Specifically what is a thyristor?

A thyristor is a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure includes four quantities of semiconductor materials, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles would be the critical parts of 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 operating status. Therefore, thyristors are widely used in various electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any semiconductor device is generally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The operating condition of the thyristor is the fact that when 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 is used in between the anode and cathode (the anode is linked to the favorable pole of the power supply, and the cathode is attached to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and the indicator light fails to illuminate. This implies that the thyristor will not be conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, and a forward voltage is used towards the control electrode (referred to as a trigger, and the applied voltage is referred to as trigger voltage), the indicator light switches on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, after 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 implies that the thyristor can continue to conduct. At the moment, in order to shut down the conductive thyristor, the power supply Ea has to be shut down or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used towards the control electrode, a reverse voltage is used in between the anode and cathode, and the indicator light fails to illuminate currently. This implies that the thyristor will not be conducting and will reverse blocking.

5. To sum up

1) Once the thyristor is subjected to a reverse anode voltage, the thyristor is in a reverse blocking state no matter what voltage the gate is subjected to.

2) Once the thyristor is subjected to a forward anode voltage, the thyristor will simply 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, as long as you will find a specific forward anode voltage, the thyristor will stay switched on whatever the gate voltage. That is, after the thyristor is switched on, the gate will lose its function. The gate only serves as a trigger.

4) Once the thyristor is on, and the primary circuit voltage (or current) decreases to close to zero, the thyristor turns off.

5) The condition for that thyristor to conduct is the fact that a forward voltage ought to be applied in between the anode and the cathode, as well as an appropriate forward voltage also need to be applied in between the gate and the cathode. To transform off a conducting thyristor, the forward voltage in between the anode and cathode has to be shut down, 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 could be equivalently viewed as composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is used in between the anode and cathode of the thyristor without applying a forward voltage towards 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 towards the control electrode currently, BG1 is triggered to produce a base current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in their 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 sent to BG1 for amplification then sent 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 the two transistors, that is, the anode and cathode of the thyristor (the dimensions of the current is in fact dependant on the dimensions of the stress and the dimensions of Ea), so the thyristor is totally switched on. This conduction process is completed in an exceedingly limited time.
2. Following the thyristor is switched on, its conductive state will likely be maintained by the positive feedback effect of the tube itself. Even when the forward voltage of 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 transform on. After the thyristor is switched on, the control electrode loses its function.
3. The only way to turn off the turned-on thyristor is to decrease the anode current that it is not enough to keep up the positive feedback process. The way to decrease the anode current is to shut down the forward power supply Ea or reverse the connection of Ea. The minimum anode current required to keep your thyristor in the conducting state is referred to as the holding current of the thyristor. Therefore, strictly speaking, as long as the anode current is under the holding current, the thyristor could be switched off.

Exactly what is the difference between a transistor and 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.

Operating conditions:

The task of any 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 in the gate to transform on or off.

Application areas

Transistors are widely used in amplification, switches, oscillators, as well as other aspects of electronic circuits.

Thyristors are mainly found in electronic circuits such as controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Way of working

The transistor controls the collector current by holding the base current to attain current amplification.

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

Circuit parameters

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 summarize, although transistors and thyristors may 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 may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Within the lighting field, thyristors may be used in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors may be used to control the current flow towards the heating element.
• In electric vehicles, transistors may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is actually one of the leading enterprises in the Home Accessory & Solar Power System, which can be fully working in the growth and development of power industry, intelligent operation and maintenance control over 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.