Time： 2019-03-12 14:33:10
The role of the power filter is to suppress electromagnetic noise.
The effects of noise can be divided into the following two types:
Immunity: To reduce the noise entering the device to such an extent that it does not cause abnormal operation of the device, such as an instrument used in a broadcasting station's transmitting device.
Emissions: To reduce the noise generated by the equipment and affect the power supply or other equipment below the allowable value of regulations (such as FCC part 15), such as noise generated by switching power supplies.
The noise to be suppressed by the line filter can be divided into the following two types:
Common mode: The noise of the same power line in two (or more) lines can be regarded as the noise of the power line to ground.
Differential mode: Noise between the power line and the power line.
The same power supply filter will have different rejection capabilities for common mode noise and differential mode noise, and will generally be described by the spectrum of the frequency corresponding to the suppression (in decibels).
The function of the power line filter is to enable the device to meet the requirements for conducted emission and conduction sensitivity in the electromagnetic compatibility standard. The power line filter is also important for suppressing the device to generate strong radiation interference.
Strictly speaking, the role of the power line filter is to prevent electromagnetic interference generated by the device itself from entering the power line, and to prevent interference on the power line from entering the device.
The power line filter is a low-pass filter that allows a DC or 50 Hz operating current to pass without allowing a higher frequency electromagnetic interference current to pass. The power line filter is bidirectional. It can prevent the interference on the power grid from entering the equipment and adversely affect the equipment, so that the equipment can meet the requirements of conduction sensitivity; and it can prevent the electromagnetic interference inside the equipment from passing. The power line is transmitted to the grid to enable the device to meet the requirements for conducted emissions. Power line filters are used for devices that generate strong interference and devices that are sensitive to outside interference. Devices capable of generating strong interference include: devices containing pulse circuits (microprocessors), devices using switching power supplies, variable frequency speed control devices, devices using thyristors, and devices containing motor motors.