When you specify a switching power supply, you design for a specific delta I
(switch current into the filter inductor) as a percentage of the total power
current.
The delta I value times the ESR of the cap determines the ripple voltage of
the supply.
The rms(delta I) determines the ripple current into the cap.
The (rms(delta I)^2 times the ESR determines the power dissipation of the
capacitor.
Cap B is the better cap for a switching power supply because it has lower
ESR and can handle higher ripple current.
However, if you're trying to remove high speed switching noise from digital
components, you need a selection of ceramic decoupling capacitors in
parallel with the electrolytic for best performance. I use a combination of
0.1 uF and 470 pF capacitors with a high self resonance.
Steve KT4FY
-----------------------------
I'm looking at two capacitors and trying to decide which would be the
better of the two for filtering digital noise in a circuit. My
knowledge level falls short in interpreting the stat sheets. Maybe
someone here is versed in the nomenclature & can help me understand.
Both caps are 100uf/16V
ESR 100kHz to 300kHz (m) (max.)
Cap A - 32
Cap B - 10
Allowable ripple current (mArms):
Cap A - 2890
Cap B - 4500
Tangent of loss angle (max.):
Cap A - 0.07
Cap B - 0.10
Leakage current (A) (max.)
Cap A - 160
Cap B - 500
I know lower ESR is better which A has, but Cap B allows a greater
ripple and leakage current which seems to me to allow less filtering.
I am thinking A is a more effective filter for digital noise But I am
guessing. If someone understands what's what here, I'd appreciate
knowing.
Thanks much,
Gary
ka1j
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