Diode swapping: ordinary diodes Vs. schotky

[gootee]

Originally Posted by SoNic_real_one

I think is more about the PCB trace series inductance. The electrolithyc capacitors have little inductance compared to those long PCB (or straight wires). That internal inductance is the ESL (series with ESR) and is given by the leads mainly.
Once you have looong PCB between the capacitor combo and the fast IC (consumer), the series inductance will "isolate" the PS capacitor from the IC (in HF domain). There will be no ringing at the source, because fast transients cannot get from consumer all the way back there. That's why, like you said too, for fast IC's, the local capacitor is important.

I was going to also mention the trace inductance as a possible resonance component, but was in a hurry and a little lazy. However, the amount of inductance is only a factor in the resonant frequency, not in whether or not something will be resonant. So having MORE total inductance doesn't favor the traces or wires over the electrolytic. The traces or wires have ESR and ESL, both of which are incrementally distributed along them. The ESR of the traces or wires is relatively constant vs frequency and will tend to damp any resonance, whereas the electrolytic's ESR basically vanishes at high frequencies. And it is very close to and in parallel with the low-ESR film cap in question. So they could resonate easily and well. And they don't necessarily need to be near the load, or anything else, to be excited well-enough to ring.

So I'd guess that both the trace inductance and the electrolytic's inductance could ring with a film cap, especially with heavy excitation. But as I explained above, the electrolytic will probably make a more-effective resonant circuit (higher Q).

I do agree that electrolytic (and basically all other) capacitors don't have much if any internal inductance except due to the distance between their leads and their lead lengths. (By the way, for those who believe that film caps must have high inductance because they are basically rolled-up foil, they usually are not that inductive, because one entire "side" of each roll is usually connected, not just the end of the roll.)

[gootee]

Oh, also, after doing a little more reading, I find that high-spreed rectifiers are much less noisy than low-speed ones, in terms of spewing RF. But the high-speed ones should also be the "soft recovery" type.