Safety capacitor (X capacitor Y capacitor) anti-high frequency interference circuit

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Safety capacitor (X capacitor Y capacitor) anti-high frequency interference circuit [Copy link]

Safety capacitors are divided into X capacitors and Y capacitors. The following figure shows the X capacitor circuit

The following figure shows the Y capacitor

The following figure shows the application circuit of X capacitors and Y capacitors. This is the 220V AC input current of the switching power supply, also known as the transient filter circuit or EMI filter. In the circuit, R1 is a varistor. L1 and L2 are ferrite coils, and FU1 is a fuse. The following figure shows the X capacitor and Y capacitor in the switching power supply.

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The role of EMI filter EMI filter is set between 220V AC power line and rectifier circuit to filter out voltage transient and high-frequency interference in the city power grid. It also prevents the high-frequency interference generated by the switch tube in the switching power supply from being transmitted to the city power grid, forming high-frequency interference to other electrical appliances. 1. Analysis of differential mode high-frequency interference signal and X capacitor circuit There are two 220V AC power lines, one is the phase line and the other is the neutral line. Two high-frequency interference signals will be generated on these two pins. And differential mode interference signal and common mode interference signal. As shown in the figure below

It can be seen from the figure that the high-frequency interference signals U1 and U2 have the same direction and are equal in size. Such two signals are called common mode signals. The high-frequency interference signals U3 and U4 have opposite directions and are equal in size. Such two signals are called differential mode signals. After the X capacitor C3 is connected to the circuit, since the frequency of the high-frequency interference signal is relatively high, the capacitive reactance of C3 to the high-frequency interference signal is small. In this way, the differential-mode high-frequency interference signal forms a loop through the X capacitor C3, as shown in the figure below, and cannot be added to the subsequent rectifier circuit, thus achieving the purpose of eliminating the differential-mode high-frequency interference signal.

2. Analysis of common-mode high-frequency interference signal and Y capacitor circuit The following figure is a schematic diagram of Y capacitor eliminating common-mode high-frequency interference signal. A common-mode high-frequency interference signal must use two Y capacitors because there are high-frequency interference signals on both the phase line and the neutral line. The common-mode high-frequency interference signal on the phase line is connected to the ground line through the Y capacitor C1, and the common-mode high-frequency interference signal on the neutral and phase lines is connected to the ground line through the Y capacitor C2. In this way, the common-mode high-frequency interference signal cannot be added to the subsequent circuit, achieving the purpose of suppressing the common-mode high-frequency interference signal.

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X capacitor requirements 347168 Y capacitor requirements 347169 3. Safety capacitor certification mark 347170