What are the types of thyristors?

Today, I will introduce to you all kinds of thyristor reports in this article, mainly including Light-Controlled Thyristor, Turn-Off Thyristors, Fast Thyristors, and Bidirectional Thyristors. By reading this article, you can have knowledge of these four thyristors. 

1. Light-Controlled Thyristor

The Light-Controlled Thyristor is also called the light-triggered thyristor, which uses a certain wavelength of light signal to replace the electrical signal to trigger the device. The volt-ampere characteristics of Light-Controlled Thyristor are the same as ordinary thyristors, except that as the light signal becomes stronger, the forward turning voltage gradually becomes lower.

Usually, the thyristor has 3 electrodes, the control electrode G, the anode A, and the cathode K. Since the control signal of the Light-Controlled Thyristor comes from the irradiation of light, there is no need to lead out the control electrode, so there are only two electrodes (anode A and cathode K). But its structure is the same as an ordinary thyristor, which is composed of 4-layer PNP type devices.

Except for the different trigger signals, the other characteristics of the Light-Controlled Thyristor are basically the same as those of ordinary thyristors. Therefore, the principle of using ordinary thyristors can be followed when using, as long as it is light-controlled.

2. Turn-Off Thyristors

The Turn-Off Thyristors is a power semiconductor device that controls the turn-on and turn-off of the device through the gate. GTO not only has the advantages of ordinary thyristors (high withstand voltage, large current, strong surge resistance, and low price), but also has the advantages of GTR (self-shutdown capability, no auxiliary shutdown circuit, convenient use), and it is used in A high-power switching device in high-voltage and large-capacity occasions. It is widely used in the fields of the inverter of electric locomotive, dynamic reactive power compensation of power grid, and high-power DC chopping speed regulation.

The structure of the Turn-Off Thyristors is the same as that of the ordinary unidirectional thyristor. It is also composed of a PNPN four-layer semiconductor. There are also three external electrodes, namely the gate G, the anode A and the cathode K. The ordinary unidirectional thyristor only constitutes a unit device, while the Turn-Off Thyristors constitute a multi-element power integrated device, which contains dozens or even hundreds of small GTO units with a common anode. In order to achieve gate-controlled turn-off, the cathode and gate of these small GTO units are specially designed to be connected in parallel inside the device.

3. Fast Thyristors

The Fast Thyristor is a derivative of the ordinary thyristor, which is mainly used for induction heating medium frequency power supply devices. It is an appliance used for higher frequency rectification, inverter, and frequency conversion circuits, and can work at frequencies above 400Hz. Depending on the current capacity, the turn-on time is 4-8 microseconds, and the turn-off time is 10-60 microseconds. It is mainly used for higher frequency rectification, chopping, inverter, and frequency conversion circuits.

The basic structure of the Fast Thyristor is similar to that of the ordinary thyristor, but to adapt to the characteristics of intermediate frequency applications, the design of the gate pattern is more complicated. Due to the use of a special process to reduce the service life, the switching characteristics of the Fast Thyristor are greatly improved, and the turn-off time is greatly shortened, but this is not conducive to the on-state characteristics of the device, inrush current, and other performance. These contradictions should be considered as a whole during device design, and users should also choose specific teaching requirements based on actual application conditions.

4. Bidirectional Thyristors

The Bidirectional Thyristors are made of N-P-N-P-N five-layer semiconductor material, and three electrodes are also drawn to the outside. The Bidirectional Thyristors are equivalent to the inverse parallel connection of two unidirectional thyristors, but there is only one control pole. The Bidirectional Thyristors, like the unidirectional thyristor, also has trigger control characteristics. However, its trigger control characteristics are very different from that of a unidirectional thyristor. This is that no matter what polarity voltage is connected between the anode and the cathode, as long as a trigger pulse is added to its control electrode, it does not care about this pulse. Whatever the polarity, the Bidirectional Thyristors can be turned on. Although the Bidirectional Thyristors can be regarded as a combination of two ordinary thyristors in form, it is actually a powerful integrated device composed of 7 transistors and multiple resistors.

At last, I also write an article about TCR22 Thyristor. If you have an interest in it you may see this. Thank you!

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