What are the functions of small thyristors and electrode pattern rectifier gates?
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What are the functions of small thyristors and electrode pattern rectifier gates?

Posted Date: 2024-02-05

Symbol of thyristor

There are many types of semiconductor components called thyristors, the most basic of which is SCR.

SCR is the abbreviation of silicon controlled rectifier, which means silicon controlled rectifier element, that is, a rectifier element with a rectifier gate. Generally speaking, thyristors refer to components such as SCR.

The picture shows a schematic diagram of a small thyristor and electrodes.

In the picture is its symbol, which has 1 more pin than the 2 pins of the diode. They are both rectifier components, so their symbols are very similar. This extra pin is called the rectifier gate (electrode), and its difference from the diode is that it can control the conduction timing between the cathode and the anode based on the signal applied to the rectifier gate.

So what does the rectifier grid do?

The picture shows a circuit that uses a thyristor to dim a light bulb. Let us analyze the role of the rectifier gate.

Now close the switch S1, but at this time the bulb neither lights up nor the ammeter pointer deflects.

Next, switch S2 is closed, and current is supplied to the rectifier grid through the rectifier grid current generating circuit. The bulb will illuminate and the pointer of the ammeter will deflect at the same time.

The above situation is shown in the figure below. The timing of turning on the cathode and anode can be controlled by the phase angle of the current applied to the rectifier grid.

By changing the phase angle of the current applied to the rectifier grid, the thyristor can change the size of the current flowing through the load even when the power supply voltage and load are fixed, that is, it can dim the light bulb to change the brightness. .

When the phase angle a1 in Figure (a) is very small, the conduction between the cathode and the anode starts earlier, the conduction time is longer, and the current flowing through the bulb (average current) is also larger, so the bulb is brighter.

In figure (b), the conduction time is very short, so the current flowing is also small, and the brightness of the bulb is darker than the former.

So, how does the phase angle of the current applied to the rectifier gate change? Let us take an example of a Toulon circuit where a rectifier gate current occurs.

Review Editor: Huang Fei


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