Author Topic: Do we still need electrolytic capacitors (for basic decoupling)?  (Read 986 times)

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Offline TheUnnamedNewbieTopic starter

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This might sound like a big of a strange question, but I have spent the last few days diving deep into the concepts of decoupling capacitors, with lots of simulations and modeling.

It got me thinking - Most LDOs have pretty good output impedance up to a few tens of kHz. Past the few tens of kHz, you are already into the regime where big electrolytic caps (especially when combined with trace inductance) are past self-resonance.

So that makes me wonder - are big electrolytics still useful? (I realize some other applications where you have high pulse-loads are a different matter entirely).
Do you still use them? Are you sure there is still a point to using them?
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Offline Siwastaja

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Re: Do we still need electrolytic capacitors (for basic decoupling)?
« Reply #1 on: April 02, 2020, 01:35:46 pm »
Great for damping resonances and peaking whenever you need to use large values of low-ESR ceramic capacitance - such as input circuitry of most switching converters.

Say, you have 100uF of ceramic capacitance - put a 470uF cheap elcap in parallel. Boom, 100% input overshoot reduced to a few %.
 
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Online David Hess

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Re: Do we still need electrolytic capacitors (for basic decoupling)?
« Reply #2 on: April 06, 2020, 02:50:23 am »
It got me thinking - Most LDOs have pretty good output impedance up to a few tens of kHz. Past the few tens of kHz, you are already into the regime where big electrolytic caps (especially when combined with trace inductance) are past self-resonance.

Just because they are past self resonance doesn't mean they are not providing useful decoupling; their impedance is still low to usefully high frequencies.

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So that makes me wonder - are big electrolytics still useful? (I realize some other applications where you have high pulse-loads are a different matter entirely).

They are hard to beat economically when bulk output capacitance is required.  I only see them entirely replaced when long life and high temperature operation is required.
 


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