What exactly is a thyristor?

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

The graphical symbol of any semiconductor device is usually represented from 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-weight-controlled thyristors. The working condition from the thyristor is the fact that when a forward voltage is used, the gate should 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 linked to the favorable pole from the power supply, and also the cathode is attached to the negative pole from the power supply). But no forward voltage is used towards the control pole (i.e., K is disconnected), and also the indicator light does not illuminate. This implies 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, along with a forward voltage is used towards the control electrode (called a trigger, and also 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, right after the thyristor is switched on, whether or not the voltage around the control electrode is taken off (that is certainly, K is switched on again), the indicator light still glows. This implies that the thyristor can continue to conduct. Currently, to be able to cut off the conductive thyristor, the power supply Ea has to be cut off 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 between the anode and cathode, and also the indicator light does not illuminate currently. This implies that the thyristor will not be conducting and will reverse blocking.

5. To sum up

1) Once the thyristor is put through a reverse anode voltage, the thyristor is at a reverse blocking state whatever voltage the gate is put through.

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

3) Once the thyristor is switched on, so long as there exists a specific forward anode voltage, the thyristor will stay switched on no matter the gate voltage. That is, right after the thyristor is switched on, the gate will lose its function. The gate only works as a trigger.

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

5) The disorder for your thyristor to conduct is the fact that a forward voltage ought to be applied between the anode and also the cathode, and an appropriate forward voltage also need to be applied between the gate and also the cathode. To transform off a conducting thyristor, the forward voltage between the anode and cathode has to be cut off, or the voltage has to be reversed.

Working principle of thyristor

A thyristor is basically a unique triode made from three PN junctions. It may be equivalently viewed as comprising a PNP transistor (BG2) and an NPN transistor (BG1).

1. When a forward voltage is used between the anode and cathode from the thyristor without applying a forward voltage towards the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still turned off because BG1 has no base current. When a forward voltage is used towards the control electrode currently, BG1 is triggered to produce a base 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 is going to be introduced the collector of BG2. This current is delivered to BG1 for amplification and after that delivered 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 big current appears within the emitters of these two transistors, that is certainly, the anode and cathode from the thyristor (the size of the current is actually dependant on the size of the load and the size of Ea), so the thyristor is totally switched on. This conduction process is finished in a really limited time.
2. Right after the thyristor is switched on, its conductive state is going to be maintained from the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it is still within the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change 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 to reduce the anode current so that it is insufficient to maintain the positive feedback process. The best way to reduce the anode current is 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 called the holding current from the thyristor. Therefore, strictly speaking, so long as the anode current is lower than the holding current, the thyristor may be turned off.

What 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 consists 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 opening and closing, allowing fast switching operations.

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

Application areas

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

Thyristors are mostly used 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 achieve current amplification.

The thyristor is switched on or off by managing 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 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 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.
• Within 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 towards the heating element.
• In electric vehicles, transistors may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a wonderful thyristor supplier. It is actually one from 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 handling of power plants, solar 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 searching for high-quality thyristor, please feel free to contact us and send an inquiry.