So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains four quantities of semiconductor components, including three PN junctions corresponding for the Anode, Cathode, and control electrode Gate. These three poles are the critical parts in 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 commonly 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 silicon-controlled rectifier is generally 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 in the thyristor is the fact that whenever a forward voltage is used, 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 in between the anode and cathode (the anode is linked to the favorable pole in the power supply, as well as the cathode is connected to the negative pole in the power supply). But no forward voltage is used for the control pole (i.e., K is disconnected), as well as the indicator light fails to light up. This implies that the thyristor will not be conducting and it has forward blocking capability.

2. Controllable conduction

As shown in Figure b above, when K is closed, as well as a forward voltage is used for the control electrode (referred to as a trigger, as well as the applied voltage is known as trigger voltage), the indicator light switches on. Which means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is switched on, whether or not the voltage on the control electrode is removed (which is, K is switched on again), the indicator light still glows. This implies that the thyristor can carry on and conduct. At this time, to be able to stop the conductive thyristor, the power supply Ea should be stop or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is used for the control electrode, a reverse voltage is used in between the anode and cathode, as well as the indicator light fails to light up currently. This implies that the thyristor will not be conducting and will reverse blocking.

5. To sum up

1) When the thyristor is subjected to a reverse anode voltage, the thyristor is at a reverse blocking state no matter what voltage the gate is subjected to.

2) When the thyristor is subjected to a forward anode voltage, the thyristor is only going to conduct once the gate is subjected to a forward voltage. At this time, the thyristor is in the forward conduction state, the thyristor characteristic, which is, the controllable characteristic.

3) When the thyristor is switched on, provided that you will find a specific forward anode voltage, the thyristor will remain switched on whatever the gate voltage. Which is, following the thyristor is switched on, the gate will lose its function. The gate only serves as a trigger.

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

5) The disorder for that thyristor to conduct is the fact that a forward voltage should be applied in between the anode as well as the cathode, plus an appropriate forward voltage also need 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 should be stop, or the voltage should be reversed.

Working principle of thyristor

A thyristor is basically a distinctive triode composed of three PN junctions. It can be equivalently viewed as consisting of a PNP transistor (BG2) plus an NPN transistor (BG1).

1. If a forward voltage is used in between the anode and cathode in the thyristor without applying a forward voltage for 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 used for 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 be introduced the collector of BG2. This current is delivered to BG1 for amplification then delivered to BG2 for amplification again. Such repeated amplification forms a vital positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A sizable current appears in the emitters of these two transistors, which is, the anode and cathode in the thyristor (the size of the current is actually dependant on the size of the stress and the size of Ea), so the thyristor is entirely switched on. This conduction process is completed in a really short period of time.
2. After the thyristor is switched on, its conductive state will be maintained from the positive feedback effect in the tube itself. Even when the forward voltage in 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. When the thyristor is switched on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor is always to lessen the anode current so that it is inadequate to keep the positive feedback process. The best way to lessen the anode current is always to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current necessary to maintain the thyristor in the conducting state is known as the holding current in the thyristor. Therefore, strictly speaking, provided that the anode current is under the holding current, the thyristor could be switched off.

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

Operating conditions:

The task of any transistor relies upon electrical signals to control its closing and opening, allowing fast switching operations.

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

Application areas

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

Thyristors are mostly utilized in electronic circuits like 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 accomplish current amplification.

The thyristor is switched on or off by managing the trigger voltage in 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 may 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 may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• Inside 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 for the heating element.
• In electric vehicles, transistors may be used in motor controllers.

Supplier

PDDN Photoelectron Technology Co., Ltd is a superb thyristor supplier. It is one in the leading enterprises in the Home Accessory & Solar Power System, which can be fully active in the progression of power industry, intelligent operation and maintenance handling of power plants, solar power and related solar products manufacturing.

It accepts payment via Charge 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.