What exactly is a thyristor?

A thyristor is a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure includes four levels of semiconductor components, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles are the critical parts of 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 various electronic circuits, like controllable rectification, AC voltage regulation, contactless electronic switches, inverters, and frequency alteration.

The graphical symbol of the Thyristor is normally represented from the text symbol “V” or “VT” (in older standards, the letters “SCR”). In addition, derivatives of thyristors also have fast thyristors, bidirectional thyristors, reverse conduction thyristors, and light-controlled thyristors. The working condition of 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 utilized involving the anode and cathode (the anode is attached to the favorable pole of the power supply, and the cathode is attached to the negative pole of the power supply). But no forward voltage is applied to the control pole (i.e., K is disconnected), and the indicator light fails to 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, and a forward voltage is applied to the control electrode (called a trigger, and the applied voltage is known as trigger voltage), the indicator light turns on. This means that the transistor can control conduction.

3. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, whether or not the voltage around the control electrode is removed (which is, K is turned on again), the indicator light still glows. This implies that the thyristor can still conduct. At the moment, to be able to cut off the conductive thyristor, the power supply Ea must be cut off or reversed.

4. Reverse blocking

As shown in Figure d above, although a forward voltage is applied to the control electrode, a reverse voltage is applied involving the anode and cathode, and the indicator light fails to glow currently. This implies that the thyristor will not be conducting and will reverse blocking.

5. In summary

1) Once the thyristor is exposed to a reverse anode voltage, the thyristor is in a reverse blocking state regardless of what voltage the gate is exposed to.

2) Once the thyristor is exposed to a forward anode voltage, the thyristor will only conduct when the gate is exposed to a forward voltage. At the moment, the thyristor is within the forward conduction state, which is the thyristor characteristic, which is, the controllable characteristic.

3) Once 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. That is certainly, following the thyristor is turned on, the gate will lose its function. The gate only functions as a trigger.

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

5) The condition for that thyristor to conduct is the fact that a forward voltage should be applied involving the anode and the cathode, as well as an appropriate forward voltage should also be applied involving the gate and the cathode. To turn off a conducting thyristor, the forward voltage involving the anode and cathode must be cut off, or perhaps the voltage must be reversed.

Working principle of thyristor

A thyristor is essentially a unique triode made up of three PN junctions. It can be equivalently regarded as composed of a PNP transistor (BG2) as well as an NPN transistor (BG1).

1. In case a forward voltage is applied involving the anode and cathode of 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. In case a forward voltage is applied to the control electrode currently, BG1 is triggered to create basics current Ig. BG1 amplifies this current, and a ß1Ig current is obtained in their 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 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 get into a saturated conduction state quickly. A large current appears within the emitters of the two transistors, which is, the anode and cathode of the thyristor (the size of the current is really determined by the size of the stress and the size of Ea), so the thyristor is totally turned on. This conduction process is finished in a very short time.
2. After the thyristor is turned on, its conductive state will be maintained from the positive feedback effect of the tube itself. Even when the forward voltage of the control electrode disappears, it really is still within the conductive state. Therefore, the function of the control electrode is just to trigger the thyristor to turn on. After the thyristor is turned on, the control electrode loses its function.
3. The best way to switch off the turned-on thyristor would be to reduce the anode current so that it is insufficient to keep the positive feedback process. The best way to reduce the anode current would be to cut off the forward power supply Ea or reverse the connection of Ea. The minimum anode current necessary to keep the thyristor within the conducting state is known as the holding current of the thyristor. Therefore, strictly speaking, provided that the anode current is lower than the holding current, the thyristor may be turned off.

What is the difference between a transistor and a thyristor?

Structure

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

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

Functioning conditions:

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

The thyristor needs a forward voltage and a trigger current on the gate to turn 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 accomplish current amplification.

The thyristor is turned on or off by managing the trigger voltage of the control electrode to realize 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 cases, because of the different structures and working principles, they have got noticeable variations 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.
• Inside the lighting field, thyristors can be utilized in dimmers and light control devices.
• In induction cookers and electric water heaters, thyristors may 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 wonderful thyristor supplier. It is one of the leading enterprises in the Home Accessory & Solar Power System, that is fully involved in the growth and development of power industry, intelligent operation and maintenance management of power plants, solar panel 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. If you are searching for high-quality thyristor, please feel free to contact us and send an inquiry.