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EMI filter selection and use of attention
Resource:EMI Filter | power filter low-pass filter phase noise filter noise filter Power line filter EMI filter socket Chengdu MengSheng Electronics Co., Ltd       Pubic Date:2015-10-09   Hits:5214

Filter selection and precautions for use

1. How to choose the power line interference filter?

Some customers think that the higher the insertion loss of EMI filter is, the better the series of filter network. In fact, this is not the right way to choose filters. Moreover, the price of more series of filter network is more expensive, and the volume and the weight are bigger. In fact, the only way to select and evaluate the power line filter is to install it on the device for testing. As mentioned above, the performance depends largely on the device load impedance. It cannot be deduced from the insertion loss data of impedance (50). It is a complex function of the impedance of filter element and the impedance of the device, and the magnitude and phase of the filter vary in frequency range. The different performance levels of FCC (VDE) and sensitivity control required by the filter selection test are carried out on the equipment.

2. Are all EMI filter networks with the same circuit and component values the same performance?

All the EMI filter networks with the same circuit and component values have different performance. Component values are specified and measured at a certain frequency (usually 1KHz), while the performance of the filter is required throughout the frequency range, not only when the component is measured. The structure of the component and the method of accessing the filter are very important to the performance of the filter.

3. Is the installation important to the performance of the EMI filter?

Installation and wiring have great influence on the performance of the filter. The power line filter is best installed on the input line of the power line of the equipment. The filter is an obstacle to the high frequency signal, and the function of the filter cannot be lost because of the discrete capacitance coupling power input line and the power supply output line or any other conductor of the protected equipment.
In the installation of power filters, we should pay attention to the following points:

1) There must be a good electrical connection between the housing of the power filter and the device. Do not install the filter on the insulation board or spray paint surface, it must be installed on the metal casing. To avoid the use of long grounding wire, this will greatly increase the grounding inductance and resistance, thereby seriously reducing common mode rejection performance of the filter. The better way is to use the metal screw and spring (star) gasket to fix the metal shielding housing of the filter firmly on the shell of the power supply entrance, or copper braid twist belt to connect with the location.

2) When the cable is bundled, it is forbidden to bundle the input and output cables of the filter. Because of this, the electromagnetic coupling between the input and output of the filter is intensified, and the filters ability to restrain the EMI signal is seriously damaged.

3) Do not install the filter in the interior of the equipment shield. Because of this, the EMI signal on the internal circuit and components of the device will be directly coupled to the device because of the EMI signal generated by the radiation on the end lead of the filter, and make the device shielding loss of suppression of EMI radiation produced by internal circuits and components.

4) It is suggested that the input and output terminals of the filter can be isolated effectively by using the original shielding of the equipment, and the possible electromagnetic coupling between the filter input and output terminals can be controlled to a minimum. Generally, the shell of the general filter is connected to the frame or casing of the protective equipment, and the wires on the wire side should be kept short and well isolated from the load side wires. The ideal isolation system is a wall mounted filter with an incoming line socket.

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