In this article, we consider selection of components to address EMI and output noise. This article concludes our discussion of the selection of components for the circuit used in design examples.
EMI countermeasures are extremely important in equipment design. Switching power supplies generate EMI given the nature of their operation by switching. There are the following three measures to address EMI.
1) Adding a filter to the input section
A common mode filter for power supplies, LC filter, or the like can be added.
Output Noise Countermeasures
The voltage rectified by the output rectifying diode DN1 is smoothed by the capacitors Cout1 and Cout2, but for further smoothing and to filter switching noise, an LC filter may be added. In this example, the LC filter is constituted from L3, 2.2 μH, and Cout3, 220 μF. Here again, component values should be adjusted while checking the influence of noise and the effectiveness of the LC filter.
・EMI countermeasures include addition of an input filter, Y capacitors, and snubbers for output rectifying diodes.
・To deal with output noise, an LC filter can be added to the output.
・In all cases, component values must be adjusted while checking the influence of noise.