So what is a thyristor?

A thyristor is actually a high-power semiconductor device, also referred to as a silicon-controlled rectifier. Its structure consists of 4 quantities of semiconductor materials, including three PN junctions corresponding towards the Anode, Cathode, and control electrode Gate. These three poles are 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 functioning status. Therefore, thyristors are commonly used in a variety of electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of a Thyristor is generally represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors also include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The functioning condition from the thyristor is the fact that when a forward voltage is applied, the gate should have a trigger current.

Characteristics of thyristor

1. Forward blocking

As shown in Figure a above, when an ahead voltage is used in between the anode and cathode (the anode is attached 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 towards the control pole (i.e., K is disconnected), and the indicator light does not 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 applied towards the control electrode (known as a trigger, and the applied voltage is referred to 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, after the thyristor is turned on, even when the voltage on the control electrode is taken off (which is, K is turned 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 must be stop 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 in between the anode and cathode, and the indicator light does not light up at the moment. This implies that the thyristor will not be conducting and may reverse blocking.

5. In conclusion

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

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

3) If the thyristor is turned on, so long as you will find a specific forward anode voltage, the thyristor will always be turned on regardless of the gate voltage. That is certainly, after the thyristor is turned on, the gate will lose its function. The gate only serves as a trigger.

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

5) The problem for your thyristor to conduct is the fact that a forward voltage should be applied in between the anode and the cathode, plus an appropriate forward voltage also need to be applied in between the gate and the cathode. To change off a conducting thyristor, the forward voltage in between the anode and cathode must be stop, or perhaps the voltage must be reversed.

Working principle of thyristor

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

1. In case a forward voltage is applied in 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 remains switched off because BG1 has no base current. In case a forward voltage is applied towards the control electrode at the moment, BG1 is triggered to generate 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 is going to be introduced the collector of BG2. This current is brought to BG1 for amplification 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, which is, the anode and cathode from the thyristor (how big the current is really based on how big the stress and how big Ea), therefore the thyristor is entirely turned on. This conduction process is completed in an exceedingly short period of time.
2. After the thyristor is turned on, its conductive state is going to be maintained by the positive feedback effect from the tube itself. Even if the forward voltage from the control electrode disappears, it really is still within the conductive state. Therefore, the function of the control electrode is only to trigger the thyristor to transform on. When the thyristor is turned on, the control electrode loses its function.
3. The only way to shut off the turned-on thyristor is to reduce the anode current so that it is insufficient to maintain the positive feedback process. The way to reduce the anode current is to stop the forward power supply Ea or reverse the link of Ea. The minimum anode current needed to keep your thyristor within the conducting state is referred to as the holding current from the thyristor. Therefore, strictly speaking, so long as the anode current is under the holding current, the thyristor can 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.

Operating conditions:

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

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

Application areas

Transistors are commonly used in amplification, switches, oscillators, along with other aspects of electronic circuits.

Thyristors are mostly used in electronic circuits like controlled rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency conversions.

Means of working

The transistor controls the collector current by holding the base current to accomplish current amplification.

The thyristor is turned 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 based on stability and reliability and usually have higher turn-off voltage and larger on-current.

To summarize, although transistors and thyristors may be used in similar applications sometimes, due to their different structures and functioning principles, they have noticeable variations in performance and utilize occasions.

Application scope of thyristor

• In power electronic equipment, thyristors may be used in frequency converters, motor controllers, welding machines, power supplies, etc.
• In the lighting field, thyristors may be used in dimmers and lightweight 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 is 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 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 looking for high-quality thyristor, please feel free to contact us and send an inquiry.