Practical Methods for Noise Suppression in Switching Power Supplies
The three elements that form electromagnetic interference are the interference source, propagation path, and disturbed equipment. Therefore, suppressing electromagnetic interference should also focus on these three aspects. Firstly, the interference source should be suppressed to directly eliminate the cause of interference; Secondly, it is to eliminate the coupling and radiation between the interference source and the 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 not within the scope of this article's discussion.
The use of power factor correction (PFC) technology and soft switching power conversion technology can greatly reduce the amplitude of noise.
(1) Measures on the circuit
The main cause of electromagnetic interference in switch mode power supplies is the rapid changes in voltage and current, so it is necessary to minimize the rate of change in voltage and current (du/dt, di/dt) in the circuit as much as possible. Using absorption circuits is also a good way to suppress electromagnetic interference. The basic principle of absorption circuit is to provide a bypass for the switch when it is turned off, absorb the energy accumulated in the parasitic distribution parameters, and thus suppress the occurrence of interference. The commonly used absorption circuits include RC, RCD, LC passive absorption networks, and active absorption networks.
Filtering is a great method for suppressing conducted interference. For example, connecting a filter to the power input terminal can suppress the interference generated by the switching power supply and feedback to the grid, as well as suppress the damage of noise from the grid to the power supply itself. In the filtering circuit, many specialized filtering components are also used, such as through-hole capacitors, three terminal capacitors, and ferrite magnetic rings, which can improve the filtering characteristics of the circuit. Proper design or selection of filters, and proper installation of filters, are important components of anti-interference technology.
