| Electronics > Beginners |
| Offline SMPS Earthing & EMC article begs for clarification |
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| T3sl4co1l:
Maybe. Note that it's not the parallel self resonant frequency (SRF), in fact that gives peak attenuation. It's somewhere above, at the first series resonant frequency. That usually happens at a high enough frequency that a ferrite bead is all that's needed (if anything at all) to at least dampen the resonance. The filter impedance is also usually low enough (i.e., the X cap, the impedance of which will be dominated by its ESL at this frequency) compared to the series resonant impedance that attenuation is still fair, even at that resonance. For the same reason (ESL), smaller X caps may be necessary, in combination with the smaller inductors (whether actual inductors, or FBs or CMC leakage). There usually isn't so much emission at such frequencies to require this treatment, and also this range is better treated with layout, transformer windup, and control of switching edges. Tim |
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