[sdiy] Typical ESR of different capacitors

[Barry Klein]

If this is for a "digital board" what really are the consequences
to it if there is more than optimum noise on the supply output??
What are the power requirements of your circuit?  If anything of
consequence a switching design may be preferrable - leading this
thread to extend on even further...

I work with power supplies most of the day.  Hate them.  :-)

Barry




-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Antti Huovilainen
Sent: Thursday, September 02, 2010 2:48 PM
To: Simon Brouwer
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Typical ESR of different capacitors

On Thu, 2 Sep 2010, Simon Brouwer wrote:

>> It's been hard / impossible to find good information online about the
topic 
>> as manufacturers tend to only list ESR for their low-ESR capacitor
models.
>
> That is not my experience. For example, the first cheap 10uF aluminium 
> electrolytic I find on the Farnell site has this datasheet: 
> http://www.farnell.com/datasheets/14936.pdf

That would be a low-esr capacitor (it even says "Low impedance" in the 
datasheet). The question was about non low-ESR capacitors like the ones 
many of us might have lying around.

> Wrt your question about dissipation factor and ESR, see 
> http://wiki.xtronics.com/index.php/Capacitors_and_ESR#Dissipation_Factor

Too bad the claims on that page don't actually match with manufacturer 
datasheets for low ESR capacitors at least.

It's obvious once you do the calculation using 100 kHz as the frequency 
where even DF of 1.0 would result in absurdly low ESR values for larger 
caps. Using 120 Hz gives much too high ESR on the other hand (1.8 ohms 
vs the actual 0.35 ohms for Panasonic FC series 100 uF / 25V)

> Up to tens of uF, consider a ceramic capacitor. They have very low ESR. 
> For higher capacitance, look for low-ESR aluminium.

Highest valued ceramic I can get locally is 1.0 uF and they're rather 
costly compared to the capacitance.

> By the way, check the datasheet of your LDO for requirements on the 
> output capacitor. Some LDO's actually need not-so-good ESR on their 
> output for stability.

Hence the need for info about typical ESR values and not just "ESR values 
of manually selected and ordered capacitors".

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova
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