Switching Power Supply Noise Suppression Methods
Formation of electromagnetic interference of the three elements are the source of interference, propagation pathway and disturbed equipment, therefore, the inhibition of electromagnetic interference should also start from these three aspects. Firstly, the source of interference should be suppressed, directly eliminating the cause of the interference; secondly, the coupling and radiation between the source of interference and disturbed equipment should be eliminated, cutting off the propagation path of electromagnetic interference; thirdly, the immunity of disturbed equipment should be improved, and its sensitivity to noise should be reduced. The third point is not the scope of this paper.
The use of power factor correction (PFC) technology and soft-switching power conversion technology can greatly reduce the noise amplitude.
(1) Measures on the circuit
The main cause of electromagnetic interference in switching power supplies is the sharp changes in voltage and current, so it is necessary to reduce the rate of change of voltage and current in the circuit (du/dt, di/dt) as much as possible. The use of absorption circuits is also a good way to suppress electromagnetic interference. The basic principle of absorption circuits is to provide a bypass for the switch when the switch is off, absorbing the energy accumulated in the parasitic distribution parameters, thereby suppressing interference. Commonly used absorption circuits are RC, RCD, LC passive absorption network and active absorption network.
Filtering is a good way to suppress conducted interference. For example, connecting a filter at the input of the power supply can suppress the interference generated by the switching power supply and fed back to the grid, as well as the noise from the grid on the power supply itself. In filter circuits, many specialised filter components are also used, such as through-core capacitors, three-terminal capacitors, and ferrite toroids, and they can improve the filtering characteristics of the circuit. Proper design or selection of filters, and correct installation of filters, is an important part of anti-interference technology.
