Reversely Switching Dynistors: A Unique Approach to Semiconductor Design

Posted on by

So what is a thyristor?

A thyristor is really a high-power semiconductor device, also known as a silicon-controlled rectifier. Its structure contains 4 quantities of semiconductor components, including three PN junctions corresponding to the Anode, Cathode, and control electrode Gate. These three poles would be 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 operating 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 the semiconductor device is usually represented by the text symbol “V” or “VT” (in older standards, the letters “SCR”). Furthermore, derivatives of thyristors include fast thyristors, bidirectional thyristors, reverse conduction thyristors, and lightweight-controlled thyristors. The operating condition from the thyristor is that each time 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 between the anode and cathode (the anode is attached to the favorable pole from the power supply, and also the cathode is linked to the negative pole from the power supply). But no forward voltage is used to the control pole (i.e., K is disconnected), and also the indicator light fails to illuminate. This demonstrates that the thyristor will not be conducting and it has forward blocking capability.

  1. Controllable conduction

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

  1. Continuous conduction

As shown in Figure c above, following the thyristor is turned on, whether or not the voltage in the control electrode is removed (that is, K is turned on again), the indicator light still glows. This demonstrates that the thyristor can continue to conduct. At this time, in order to stop the conductive thyristor, the power supply Ea has to be stop or reversed.

  1. Reverse blocking

As shown in Figure d above, although a forward voltage is used to the control electrode, a reverse voltage is used between the anode and cathode, and also the indicator light fails to illuminate currently. This demonstrates that the thyristor will not be conducting and may reverse blocking.

  1. In summary

1) When the thyristor is subjected to a reverse anode voltage, the thyristor is in 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 when the gate is subjected to a forward voltage. At this time, 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 there exists a specific forward anode voltage, the thyristor will stay turned on no matter the gate voltage. Which is, following the thyristor is turned on, the gate will lose its function. The gate only works as a trigger.

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

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

Working principle of thyristor

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

  1. If a forward voltage is used between the anode and cathode from the thyristor without applying a forward voltage to the control electrode, although both BG1 and BG2 have forward voltage applied, the thyristor is still switched off because BG1 has no base current. If a forward voltage is used to the control electrode currently, BG1 is triggered to create basics 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 introduced the collector of BG2. This current is sent to BG1 for amplification and then sent to BG2 for amplification again. Such repeated amplification forms a crucial positive feedback, causing both BG1 and BG2 to get in a saturated conduction state quickly. A big current appears inside the emitters of these two transistors, that is, the anode and cathode from the thyristor (the dimensions of the current is really determined by the dimensions of the load and the dimensions of Ea), therefore the thyristor is entirely turned on. This conduction process is completed in an exceedingly short period of time.
  2. Following the thyristor is turned on, its conductive state will be maintained by the positive feedback effect from the tube itself. Even when the forward voltage from the control electrode disappears, it really is still inside the conductive state. Therefore, the function of the control electrode is simply to trigger the thyristor to change on. When the thyristor is turned on, the control electrode loses its function.
  3. The best way to shut off the turned-on thyristor would be to decrease the anode current so that it is not enough to keep up the positive feedback process. How you can decrease the anode current would be to stop the forward power supply Ea or reverse the bond of Ea. The minimum anode current needed to maintain the thyristor inside the conducting state is called the holding current from the thyristor. Therefore, as it happens, provided that the anode current is less than the holding current, the thyristor could be switched off.

What exactly is the difference 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 composed of four PNPN structures of semiconductor materials, including anode, cathode, and control electrode.

Functioning conditions:

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

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

Application areas

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

Thyristors are mostly utilized 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 achieve current amplification.

The thyristor is turned on or off by controlling the trigger voltage from 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 instances, due to their different structures and operating principles, they may have 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 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 wonderful thyristor supplier. It is one from the leading enterprises in the Home Accessory & Solar Power System, which is fully involved in the growth and development of power industry, intelligent operation and maintenance handling of 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.