Inseparable good brothers - X capacitors and Y capacitors

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Inseparable good brothers - X capacitors and Y capacitors [Copy link]

Preface

As long as it is a circuit board connected to 220V, you will generally see the presence of safety capacitors. The yellow ones are X capacitors and the blue ones are Y capacitors.

X and Y capacitors are generally used in circuits as follows

02

What is a safety capacitor?

Understand "safety capacitors" literally (it is nothing more than capacitors that meet safety regulations)

Among them, safety capacitors can be divided into X capacitors and Y capacitors.

There are many types of capacitors. X capacitors are essentially polyester capacitors, and Y capacitors are essentially ceramic capacitors.

The internal medium of polyester capacitor is polyester

The internal medium of the ceramic capacitor is ceramic

03

What is the function of safety capacitors?

The function of safety capacitors is to filter out high-frequency interference (these interferences may come from interference caused by lightning or interference caused by plugging and unplugging)

The X capacitor is connected between the live wire and the neutral wire.

The Y capacitor is connected between the live wire and the ground wire, and between the neutral wire and the ground wire.

It can be seen that the X capacitor plays the role of differential mode interference in the circuit, while the Y capacitor plays the role of common mode interference.

Let's look at the X capacitor first. If a high-frequency interference signal appears on the live wire, the flow direction is as shown in the figure.

The amplitude of the high-frequency signal before and after the X capacitor does not change, but the phase difference is 180 degrees.

The so-called "differential mode" means that the phase difference is 180 degrees

Looking at the Y capacitor again, the amplitude and phase of the high-frequency signal on the live wire and the neutral wire are the same (that is, synchronous)

The so-called "common mode" means that the amplitude, phase and frequency are the same

Since the interference of the live wire and the neutral wire is the same, the X capacitor will not work at this time

Because the ground wire can be regarded as zero potential, and because of the potential difference, a capacitor can be connected between the live wire and the ground wire, so that the high-frequency signal can be filtered out. The same is true for the neutral wire.

04

Can other capacitors be used instead of safety capacitors?

The answer is no, because other capacitors have positive and negative points. If they are connected in reverse, you can imagine what will happen. However, safety capacitors have no positive and negative points.

In addition, X capacitors cannot replace Y capacitors because the withstand voltage of Y capacitors is greater than that of X capacitors.

05

Summarize

X capacitors are used to filter differential mode interference

Y capacitors are used to filter out common mode interference

X capacitor has a larger capacitance than Y capacitor, but its withstand voltage is smaller than Y capacitor.

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miaods2002

Very well written! I didn't have a clear concept of X and Y capacitors before, but after reading this article, I suddenly understood. Thank you for sharing!!!