What exactly is a thyristor?

A thyristor is really a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure consists of four levels of semiconductor elements, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles are definitely 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 working status. Therefore, thyristors are widely used in a variety of electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the semiconductor device is usually represented through 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 working condition of the thyristor is the fact that whenever 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 in between the anode and cathode (the anode is attached to the favorable pole of the power supply, as well as the cathode is linked to the negative pole of the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), as well as the indicator light fails to light up. This shows that the thyristor is not really 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 towards the control electrode (referred to as a trigger, as well as the applied voltage is referred to 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, right after the thyristor is turned on, even if the voltage around the control electrode is taken off (that is certainly, K is turned on again), the indicator light still glows. This shows that the thyristor can still conduct. Currently, in order to stop the conductive thyristor, the power supply Ea has to be stop 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, as well as the indicator light fails to light up at this time. This shows that the thyristor is not really conducting and may reverse blocking.

5. To sum up

1) If the thyristor is exposed to a reverse anode voltage, the thyristor is at a reverse blocking state whatever voltage the gate is exposed to.

2) If the thyristor is exposed to a forward anode voltage, the thyristor will simply conduct when the gate is exposed to a forward voltage. Currently, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) If the thyristor is turned on, as long as you will find a specific forward anode voltage, the thyristor will always be turned on whatever the gate voltage. That is, right after the thyristor is turned on, the gate will lose its function. The gate only functions as a trigger.

4) If 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 your thyristor to conduct is the fact that a forward voltage should be applied in between the anode as well as the cathode, and an appropriate forward voltage ought to be applied in between the gate as well as the cathode. To turn off a conducting thyristor, the forward voltage in 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 a unique triode composed of three PN junctions. It may be equivalently viewed as composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. When 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. When a forward voltage is used towards 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 their collector. This current is precisely the base current of BG2. After amplification by BG2, a ß1ß2Ig current is going to be brought in the collector of BG2. This current is brought to BG1 for amplification then brought 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 large current appears in the emitters of these two transistors, that is certainly, the anode and cathode of the thyristor (the size of the current is in fact dependant on the size of the load and the size of Ea), so the thyristor is completely turned on. This conduction process is finished in a really short time.
2. After the thyristor is turned on, its conductive state is going to 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 in the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to transform on. After the thyristor is turned on, the control electrode loses its function.
3. The only method to switch off the turned-on thyristor is to reduce the anode current so that it is not enough to keep the positive feedback process. The way to reduce the anode current is to stop the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to maintain the 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 lower than the holding current, the thyristor may be switched off.

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

Structure

Transistors usually contain a PNP or NPN structure composed of three semiconductor materials.

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

Working conditions:

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 and a trigger current on the gate to transform on or off.

Application areas

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

Thyristors are mostly utilized in electronic circuits including 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 achieve current amplification.

The thyristor is turned on or off by controlling the trigger voltage of the control electrode to comprehend 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 sum up, although transistors and thyristors may be used in similar applications in some cases, because of the different structures and working principles, they have 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 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 an excellent thyristor supplier. It really is one of the leading enterprises in the Home Accessory & Solar Power System, which can be fully involved in the development of power industry, intelligent operation and maintenance management of power plants, solar power panel and related solar products manufacturing.

It accepts payment via Bank 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.