Author Topic: SMD DC Power filtering caps  (Read 1247 times)

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Offline paulca

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Re: SMD DC Power filtering caps
« Reply #25 on: February 23, 2018, 09:37:33 am »
So if I don't put a bulk input filter on the board it will be about 3 feet away from the one in the wall wart.

Can I then get away with just a 330nF on the reg input side?

On the output side, can I use just one 100nF across the power to the ATTiny, in place of the reg output cap and the ATTiny power filter cap?  They are like 10mm apart at most.
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Online T3sl4co1l

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Re: SMD DC Power filtering caps
« Reply #26 on: February 23, 2018, 12:40:19 pm »
Recommend > 10uF electrolytic at input, that's OK at output or use another electrolytic.

Tim
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Offline David Hess

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Re: SMD DC Power filtering caps
« Reply #27 on: February 23, 2018, 03:46:25 pm »
Recommend > 10uF electrolytic at input, that's OK at output or use another electrolytic.

Or maybe a little more at the input but for a subtle reason which has nothing to do with regulator stability.

Some transformer wall warts have an alarming amount of leakage inductance so if the load on the output of the regulator is abruptly removed, the input voltage can rise high enough to burn out the regulator unless there is some bulk input capacitance to absorb it.  Bob Pease wrote about this once.

 

Online T3sl4co1l

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Re: SMD DC Power filtering caps
« Reply #28 on: February 23, 2018, 07:41:21 pm »
Or maybe a little more at the input but for a subtle reason which has nothing to do with regulator stability.

Some transformer wall warts have an alarming amount of leakage inductance so if the load on the output of the regulator is abruptly removed, the input voltage can rise high enough to burn out the regulator unless there is some bulk input capacitance to absorb it.  Bob Pease wrote about this once.

I elaborated on inrush and such earlier, for which 10uF would be borderline, and more would be just fine.

Was that in this thread, or the other?  I don't even remember anymore, these questions all blur together ::) :P

Tim
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Offline paulca

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Re: SMD DC Power filtering caps
« Reply #29 on: February 23, 2018, 09:27:50 pm »
Either way I'm back to my first post.

The only reason I asked is not that the electrolytic caps are too expensive, it's just that when I see things being suspiciously expensive I wonder if it's because I'm picking the wrong (rare, low demand) part.

Further looking capacitors seem to vary in price dramatically.  There are 100nF multi-layers that cost £0.012 in a strip of 100, but there are ones that don't look any different from spec which are £0.19 each!

I would buy a cheap chinese multi-pack, but I doubt very much I will use most of the values.  Ideally I'd like a kit which has 100 each of the 10 most used values.

1, 10, 100, 330, 1000 uF
10, 100nF
22pF

Is about all I have ever had to use so far.

However the pF, nF packs are at least cheap.

How risky would a pack of surface mount aluminium caps from china be?
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Current Open Projects:  3 Channel Audio mixer with DAC, BT, pre-amps and h/phone amp, WS281x LED controller Version 2 5V/5A w/Atmega328, FY6600 Power supply, 5A DC Load (Still!)
 

Offline soubitos

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Re: SMD DC Power filtering caps
« Reply #30 on: February 24, 2018, 07:47:21 am »
How risky would a pack of surface mount aluminium caps from china be?

Depends on what you buy from whom you buy it and what you expect to get...
I am sure brands like CapXon ChengX might not be top notch but for normal use, in non critical applications they are more than fine. Then you got Lelon, Rubycon brands that are not really Chinese but you can source them from China at good prices.. the problem is, if you can trust the average aliexpress seller to send you genuine parts ... for the most part, if the price is too good to be true, and the seller sells odd bits of products... avoid it...
 

Offline paulca

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Re: SMD DC Power filtering caps
« Reply #31 on: February 24, 2018, 08:43:33 am »
So I made about my 5th attempt to layout the board.



"Piper" by the way is my daughter.  This is her comfort night light.  She is 7 months old.
"What could possibly go wrong?"
Current Open Projects:  3 Channel Audio mixer with DAC, BT, pre-amps and h/phone amp, WS281x LED controller Version 2 5V/5A w/Atmega328, FY6600 Power supply, 5A DC Load (Still!)
 


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