What is safety capacitor? And what is the function of it?

As long as the circuit board is connected to 220Vac, you will usually see the existence of safety capacitor.

What is a safety capacitor?

Understanding 'Safety Capacitor' (nothing more than a capacitor that meets safety regulations)

A safety capacitor can be subdivided into an X-capacitor and a Y-capacitor.

Capacitors have a variety of classifications, X capacitance is essentially polyester capacitors, Y capacitance is essentially ceramic capacitors

Polyester capacitor internal medium is polyester

Porcelain chip capacitors are made of porcelain chips.

What is the function of a safety capacitor?

The role of the safety capacitor is to filter out high-frequency interference (these interferences may come from the interference generated by lightning or the interference generated by the plugging).

The X capacitor is connected between the fire wire and the zero wire.

The Y capacitor is connected between the fire and ground wires, and the zero and ground wires, respectively.

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.

The amplitude of the high-frequency signal before and after the X-capacitor remains the same, but the phase difference is 180 degrees.

The so-called 'differential mode' is a phase difference of 180 degrees.

Looking at the Y capacitor again, the amplitude and phase of the high frequency signals on the Fire and Zero wires are the same (i.e. synchronized).

The so-called 'common mode' is that the amplitude and phase frequency are the same.

Since the interference on the firewire and zero line is the same, the X capacitor will not work at this time.

Because the ground line can be regarded as zero potential, and due to the existence of potential difference, so you can connect capacitors between the fire line and the ground line, so that the high-frequency signal can be filtered out, and the same for the zero line.

Can I use other capacitors instead of safety capacitors?

The answer is no, because other capacitors have positive and negative points, if connected to the opposite, it can be imagined, while the safety capacitors do not have positive and negative points.

In addition, X capacitor can not replace Y capacitor, because Y capacitor's withstand voltage value is larger than X capacitor.

Summarize: X capacitor is used to filter out differential mode.

X capacitor is used to filter out differential mode interference

Y capacitor is used to filter common mode interference

X capacitor is larger than Y capacitor, but smaller than Y capacitor.