Just what is a thyristor?

A thyristor is really a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of four levels of semiconductor components, including 3 PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These 3 poles would be 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 widely used in a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversion.

The graphical symbol of any Thyristor is usually 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 functioning condition in the thyristor is that each time 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 involving the anode and cathode (the anode is connected 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 used to the control pole (i.e., K is disconnected), and the indicator light will not glow. This implies 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 used to the control electrode (referred to as a trigger, and 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 excited, even when the voltage on the control electrode is taken off (which is, K is excited again), the indicator light still glows. This implies that the thyristor can carry on and 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 to the control electrode, a reverse voltage is used involving the anode and cathode, and the indicator light will not glow currently. This implies that the thyristor will not be conducting and may reverse blocking.

5. In summary

1) If 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) If the thyristor is put through a forward anode voltage, the thyristor will only conduct if the gate is put through a forward voltage. At the moment, the thyristor is within the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

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

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

5) The problem for your thyristor to conduct is that a forward voltage needs to be applied involving the anode and the cathode, as well as an appropriate forward voltage also need to be applied involving the gate and the cathode. To transform off a conducting thyristor, the forward voltage involving the anode and cathode has to be shut down, or the voltage has to be reversed.

Working principle of thyristor

A thyristor is actually an exclusive triode made up of three PN junctions. It may be equivalently regarded as consisting of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. When a forward voltage is used involving the anode and cathode in the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor continues to be turned off because BG1 has no base current. When a forward voltage is used to the control electrode currently, BG1 is triggered to produce basics current Ig. BG1 amplifies this current, as well as a ß1Ig current is obtained in its 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 delivered to BG1 for amplification and after that delivered 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 inside the emitters of the two transistors, which is, the anode and cathode in the thyristor (the size of the current is actually based on the size of the load and the size of Ea), so the thyristor is entirely excited. This conduction process is finished in a very short time.
2. Following the thyristor is excited, its conductive state will likely be maintained by the positive feedback effect in the tube itself. Even if the forward voltage in the control electrode disappears, it is actually still inside the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to transform on. Once the thyristor is excited, the control electrode loses its function.
3. The only method to shut off the turned-on thyristor is to reduce the anode current so that it is not enough to keep up the positive feedback process. The way to reduce the anode current is to shut down the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep your thyristor inside the conducting state is referred to as the holding current in the thyristor. Therefore, as it happens, so long as the anode current is less than the holding current, the thyristor can be turned off.

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

Structure

Transistors usually consist of a PNP or NPN structure made up of three semiconductor materials.

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

Operating conditions:

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

The thyristor requires a forward voltage as well as 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 like 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 excited or off by manipulating the trigger voltage in 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 can be utilized in similar applications in some instances, because of the different structures and functioning principles, they have got 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.
• Within the lighting field, thyristors can be utilized in dimmers and lightweight control devices.
• In induction cookers and electric water heaters, thyristors can be used to control the current flow to the heating element.
• In electric vehicles, transistors can be utilized in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It really is one in the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the progression of power industry, intelligent operation and maintenance control over 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. Should you be looking for high-quality thyristor, please feel free to contact us and send an inquiry.