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Old 12th June 2009, 10:43 PM   #1
HaLo6 is offline HaLo6  United States
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Default Too much capacitance?

I am building a Sigma11 from AMB Labs, C5 is specified as 1 x 2700uF at 63V or 2x1500uF at 63V ... is it a big deal to do two 2200uF at 50V? I am not worried about voltage on the caps because I am configuring it for 5V DC but is the extra capacitance a big deal, I am inclined to say no... but I am not sure of the background EE theory in PS design...
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Old 12th June 2009, 11:14 PM   #2
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I don't know what a Sigma11 is, but it will probably work. But why do you what to use two 2200uF caps when one will do?

An EE might tell you that in some cases the ESR of the output cap can effect stability. In fact, an ESR of 0 may cause a regulated supply to become unstable.
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Old 13th June 2009, 12:29 AM   #3
HaLo6 is offline HaLo6  United States
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well I didnt know if 2700uF-3000uF was a minimum? I was wondering if 2200uF would be enough too...
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Old 13th June 2009, 01:02 AM   #4
infinia is offline infinia  United States
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Default Re: Too much capacitance?

Quote:
Originally posted by HaLo6
2x1500uF at 63V ... is it a big deal to do two 2200uF at 50V? I am not worried about voltage on the caps because I am configuring it for 5V DC but is the extra capacitance a big deal, I am inclined to say no... but I am not sure of the background EE theory in PS design...
It helps to post schematics and any other helpful links so we dont have to assume and/or hunt. Which I didn't bother
3000 to 4400 uF is about an increase of 50% not in excess when considering initial tolerances plus aging of these bulk caps.

I would question such a drastic change in DC voltage from 50- 60V to 5V tho? I think with this kind of change there is whole lot more to consider. Is this a linear or SMPS
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Old 13th June 2009, 01:17 AM   #5
HaLo6 is offline HaLo6  United States
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That is the rating on the caps... I am only using a 2x6VAC trafo. Schematic attached sorry.. I should have put up a link...

your signature quote is right up my alley
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File Type: png s11_sch.png (71.6 KB, 502 views)
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Old 13th June 2009, 01:22 AM   #6
HaLo6 is offline HaLo6  United States
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The caps are smoothing caps if that matters...
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Old 13th June 2009, 01:26 AM   #7
infinia is offline infinia  United States
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Yup... a whole lot more to consider.
What's the application?

12Vac>5Vdc not going to be very eff and/or hot
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Old 13th June 2009, 03:56 AM   #8
HaLo6 is offline HaLo6  United States
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That is the smallest toroid I have found and the PSU does have some pretty large heatsinks... Sigma 11

I am going to use it to power the digital section of a TPA Buffalo32 DAC
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Old 13th June 2009, 09:37 AM   #9
infinia is offline infinia  United States
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OK since this is very low power and you have quite a bit of V overhead you should be fine, if D5 and R10 appear on their charts for 5V output.
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Old 13th June 2009, 10:26 AM   #10
AndrewT is offline AndrewT  Scotland
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6Vac might be a bit too low for a regulated output of 5Vdc
Try to find 7Vac to 9Vac for this output voltage.

You can just about use 16Vdc caps for the smoothing at these low voltages.

The worst case voltage from 9Vac is ~ 9 * 1.414 * 1.3 * 1.06 -1 ~=16.5Vpk
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