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 3 PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These 3 poles would be the critical parts from 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 different electronic circuits, including controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a silicon-controlled rectifier is generally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Additionally, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The working condition from the thyristor is the fact that each time 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 can be used between the anode and cathode (the anode is linked to the favorable pole from the power supply, and the cathode is connected to the negative pole from the power supply). But no forward voltage is applied for the control pole (i.e., K is disconnected), and the indicator light does not illuminate. This demonstrates that the thyristor will not be conducting and contains forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is applied for the control electrode (referred to as a trigger, and 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 turned on, whether or not the voltage around the control electrode is removed (that is, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can still conduct. Currently, 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 applied for the control electrode, a reverse voltage is applied between the anode and cathode, and the indicator light does not illuminate at this time. This demonstrates that the thyristor will not be conducting and will reverse blocking.

5. In summary

1) When the thyristor is subjected to a reverse anode voltage, the thyristor is in a reverse blocking state whatever voltage the gate is subjected to.

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

3) When the thyristor is turned on, provided that you will find a specific forward anode voltage, the thyristor will always be turned on no matter the gate voltage. Which is, right after the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

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

5) The problem for the thyristor to conduct is the fact that a forward voltage needs to be applied between the anode and the cathode, and an appropriate forward voltage ought to be applied between the gate and the cathode. To turn off a conducting thyristor, the forward voltage 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 actually a unique triode made from three PN junctions. It may be equivalently regarded as composed of a PNP transistor (BG2) and an NPN transistor (BG1).

1. If a forward voltage is applied between the anode and cathode from the thyristor without applying a forward voltage for the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor remains turned off because BG1 has no base current. If a forward voltage is applied for the control electrode at this time, BG1 is triggered to create a base current Ig. BG1 amplifies this current, as well as 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 be brought in the collector of BG2. This current is brought to BG1 for amplification and then brought to BG2 for amplification again. Such repeated amplification forms an essential positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A large current appears in the emitters of the two transistors, that is, the anode and cathode from the thyristor (how big the current is actually based on how big the burden and how big Ea), therefore the thyristor is totally turned on. This conduction process is finished in a really short time.
2. After the thyristor is turned on, its conductive state will be maintained by the positive feedback effect from the tube itself. Whether or not the forward voltage from the control electrode disappears, it really is still in the conductive state. Therefore, the purpose of the control electrode is just to trigger the thyristor to turn on. When the thyristor is turned on, the control electrode loses its function.
3. The only method to switch off the turned-on thyristor is to lessen the anode current that it is not enough to maintain the positive feedback process. The way to lessen the anode current is to shut down the forward power supply Ea or reverse the bond of Ea. The minimum anode current needed to keep your thyristor in the conducting state is called the holding current from the thyristor. Therefore, as it happens, provided that the anode current is lower than the holding current, the thyristor may be turned off.

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

Structure

Transistors usually contain 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 task of a transistor relies on electrical signals to control its opening and closing, allowing fast switching operations.

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

Application areas

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

Thyristors are mainly found in electronic circuits including 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 manipulating the trigger voltage from 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 summarize, although transistors and thyristors can be used in similar applications in some cases, because of their different structures and working principles, they have noticeable differences in performance and make use of occasions.

Application scope of thyristor

• In power electronic equipment, thyristors can be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors can be used in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors could be used to control the current flow for the heating element.
• In electric vehicles, transistors can 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, that is fully involved in the progression of power industry, intelligent operation and maintenance control over 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.