Suppression method of switching power supply noise
The three factors that form electromagnetic interference are interference source, propagation path and disturbed equipment, so the suppression of electromagnetic interference should also start from these three aspects. First of all, we should suppress the interference sources and directly eliminate the interference causes; Secondly, eliminate the coupling and radiation between interference source and disturbed equipment, and cut off the propagation path of electromagnetic interference; The third is to improve the anti-interference ability of the disturbed equipment and reduce its sensitivity to noise. The third point is beyond the scope of this article.
Power factor correction (PFC) technology and soft-switching power conversion technology can greatly reduce the noise amplitude.
(1) Measures on the circuit
The main reason of electromagnetic interference in switching power supply is the sharp change of voltage and current, so it is necessary to reduce the change rate of voltage and current (du/dt, di/dt) in the circuit as much as possible. Using absorption circuit is also a good way to suppress electromagnetic interference. The basic principle of the absorption circuit is to provide a bypass for the switch when the switch is off, and absorb the energy accumulated in the parasitic distribution parameters, thus suppressing the interference. Commonly used absorption circuits include RC, RCD, LC passive absorption network and active absorption network.
Filtering is a good method to suppress conducted interference. For example, connecting a filter to the input of the power supply can suppress the interference generated by the switching power supply and fed back to the power grid, and can also suppress the noise from the power grid from harming the power supply itself. In the filter circuit, many special filter elements are used, such as feedthrough capacitor, three-terminal capacitor and ferrite magnetic ring, which can improve the filter characteristics of the circuit. Proper design or selection of filters and correct installation of filters are important components of anti-jamming technology.
