Switching Power Supply Filter

Switching power supply electromagnetic interference filter is a passive network, which has two way suppression performance. Insert it in the AC grid
Between the power supply, the equivalent of the EMI noise between the two plus a blocking barrier, such a simple no
The source filter has been used to suppress the noise, so that it is widely used in various electronic devices.
Due to high power consumption, low power consumption, small size, light weight, wide voltage range, flexible circuit and other characteristics, wide
Widely used in computer, communications and other electronic equipment. But with the switching power supply of small, switch to high frequency
By this high frequency, the fundamental wave itself is a source of interference.
By improving the components to achieve high frequency of the same,
Also because of the radiation interference wave and lead to a super standard value of the
Signal. These signals form an electromagnetic interference
(EMI)
, the object is the radio communication. In order to make the radio wave
Electromagnetic interference, it is to take measures to limit the electromagnetic interference, so that the electromagnetic compatibility
(EMC)
Standard
Or specification, which has become an increasingly concerned problem for electronic product designers.
Characteristics of electromagnetic interference (EMI) for switching power supply
Switching frequency of the power semiconductor device in the switching power converter is usually high,
Power switch device is inevitable to produce powerful electromagnetic interference in the process of high frequency and high frequency. Compared with the digital circuit, switching power supply EMI presents a distinct characteristic:
A. switching power supply EMI interference source location is clear, mainly in the power switch device,
Diodes, and the heat sink and high frequency transformer connected to it.
B. as working in the switch state of energy conversion device, switching power supply voltage and current change rate is very high, its EMI noise signal has both a wide frequency range, and have a certain strength.
C. printed circuit board wiring is the main reason for the electromagnetic interference. These disturbances are caused by the interference of conduction and radiation to other electronic devices.
Any power line interference signal, which can be expressed by differential mode and common mode signal. In general, differential mode interference
Small amplitude, low frequency, caused by small interference; common mode interference amplitude is large, high frequency, but also can be generated through the lead
Radiation, caused by large interference. Therefore, to weaken the conduction interference, the EMI signal control in the
The most effective method is to install an electromagnetic interference filter in the input and output circuit of the switching power supply input and output circuit of the EMC standard.

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