Just what is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four quantities of semiconductor materials, including 3 PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These 3 poles are 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 functioning status. Therefore, thyristors are popular in a variety of electronic circuits, such as controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any semiconductor device is normally represented through the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-weight-controlled thyristors. The functioning condition in the thyristor is the fact that whenever a forward voltage is applied, 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 between the anode and cathode (the anode is attached to the favorable pole in the power supply, and the cathode is connected to the negative pole in the power supply). But no forward voltage is applied towards the control pole (i.e., K is disconnected), and the indicator light fails to glow. This shows that the thyristor will not be conducting and has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is applied towards the control electrode (called a trigger, and the applied voltage is called 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 excited, even when the voltage in the control electrode is removed (that is certainly, K is excited again), the indicator light still glows. This shows that the thyristor can still 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 applied towards the control electrode, a reverse voltage is applied between the anode and cathode, and the indicator light fails to glow currently. This shows that the thyristor will not be conducting and can reverse blocking.

5. To sum up

1) When the thyristor is put through a reverse anode voltage, the thyristor is in a reverse blocking state regardless of what voltage the gate is put through.

2) When the thyristor is put through a forward anode voltage, the thyristor will only conduct when the gate is put through a forward voltage. Currently, the thyristor is in the forward conduction state, which is the thyristor characteristic, that is certainly, the controllable characteristic.

3) When the thyristor is excited, so long as you will find a specific forward anode voltage, the thyristor will remain excited no matter the gate voltage. Which is, after the thyristor is excited, the gate will lose its function. The gate only functions as a trigger.

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

5) The condition for the thyristor to conduct is the fact that a forward voltage needs to be applied between the anode and the cathode, as well as an appropriate forward voltage ought to be applied between the gate and the cathode. To transform 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 composed of three PN junctions. It could be equivalently thought to be composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. If a forward voltage is applied between the anode and cathode in 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. If a forward voltage is applied towards the control electrode currently, BG1 is triggered to create a base current Ig. BG1 amplifies this current, as well as 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 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 crucial positive feedback, causing both BG1 and BG2 to enter a saturated conduction state quickly. A large current appears within the emitters of these two transistors, that is certainly, the anode and cathode in the thyristor (how big the current is in fact determined by how big the burden and how big Ea), so the thyristor is entirely excited. This conduction process is done in a very short period of time.
2. After the thyristor is excited, its conductive state will be maintained through the positive feedback effect in the tube itself. Even when the forward voltage in the control electrode disappears, it really is still within the conductive state. Therefore, the purpose of the control electrode is simply to trigger the thyristor to turn on. Once the thyristor is excited, the control electrode loses its function.
3. The only method to shut off the turned-on thyristor would be to reduce the anode current so that it is insufficient to keep the positive feedback process. How you can reduce the anode current would be to cut off the forward power supply Ea or reverse the bond 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 under the holding current, the thyristor could be switched off.

What exactly is the difference between a transistor as well as a thyristor?

Structure

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

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

Functioning conditions:

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

The thyristor needs a forward voltage as well as a trigger current at the gate to turn on or off.

Application areas

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

Thyristors are mainly used 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 excited or off by controlling the trigger voltage in the control electrode to comprehend the switching function.

Circuit parameters

The circuit parameters of thyristors are based on stability and reliability and usually have higher turn-off voltage and larger on-current.

To sum up, although transistors and thyristors can be utilized in similar applications sometimes, because of their different structures and functioning principles, they may have noticeable differences in performance and use occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be utilized in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors can be utilized in dimmers and light-weight control devices.
• In induction cookers and electric water heaters, thyristors could be used to control the current flow towards the heating element.
• In electric vehicles, transistors can be utilized in motor controllers.

Supplier

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