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Old 4th May 2011, 02:41 PM   #1
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Default what kind of caps/inductors?

Hi there what kind of caps/inductors should I be aiming to use on a given build?

I will probably be pursuing this build, and I am limited by what is available at some reasonable price (you can buy 400$ tantalum caps which is crazy) on digikey.

There are many kinds of caps for instance, tantalum, film, ceramic etc.
there is Low ESR, Low ESL, low tolerance etc
Same goes for inductors.

I attached the schematic.
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Old 4th May 2011, 04:32 PM   #2
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For capacitors you should use low ESR X7R multilayer ceramic capacitors. I don't know so much about the inductors so I can't answer that.

Regards,

Simon H.A.
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Old 4th May 2011, 07:01 PM   #3
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Like Simon says, you want low ESR X7R ceramics wherever possible. That means pretty much every cap except the input caps, the >10uF decoupling cap on AVCC, and the >470uF PVCC caps. The AVCC cap should be either low ESR tantalum or low ESR electrolytic, bypassed with 100nF ceramic.

Cap tolerance isn't very important in this application (IMO).

Inductor cores should be Micrometals type 2, or you can try shielded ferrite bobbin cores like I used.
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Old 4th May 2011, 08:17 PM   #4
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Do you recommend X7R because that is the lowest Letter than comes in low ESR? (as opposed to X7D)
On these non-input caps how much margin do i need in voltage? I have always doubled the needed voltage on inputs but is it the same for audio?

Anonymus you had inductors on your build? for a cut-off?
I can seem to find any "Micrometals type 2" on digikey... are these just fixed inductors?
EDIT: the speaker output is 12V to my understanding so i would go with a 25V cap.

Last edited by chico1st; 4th May 2011 at 08:36 PM.
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Old 4th May 2011, 10:12 PM   #5
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Quote:
Originally Posted by chico1st View Post


I can seem to find any "Micrometals type 2" on digikey... are these just fixed inductors?
Look on ebay for t106-2 inductor cores.
You iwll need 1-2 meters of 18SWG enamel coated copper wire too.
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Old 4th May 2011, 11:06 PM   #6
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do you need to make your own inductors? does it make a big difference?
I would prefer to be lazy and just something off digikey, unless its like night and day.
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Old 4th May 2011, 11:13 PM   #7
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Quote:
Originally Posted by chico1st View Post
do you need to make your own inductors? does it make a big difference?
I would prefer to be lazy and just something off digikey, unless its like night and day.
I couldnt find one online, all I could find was very small class d inductors or power indcutors which got red hot 120 degrees c !

Its not difficult to wind your own, just keep the winding as tight as you can.
1.5 meters is enough wire. Takes me 5 minutes to wind one. Its much cheaper as well to wind your own.
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Old 5th May 2011, 12:09 AM   #8
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what really, what causes the heat? You can get them with very low DC resistance (<50mohm) if thats what causes the heat but i guess its all the switching.

These are under 2$ and are at least rated for 3 amps.

Regarding the caps, you say that the capacitor tolerance doesnt matter so then why does it matter if they are X7R?
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Old 5th May 2011, 12:17 AM   #9
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My class d amp goes upto 12 amps so needs a higher power inductor.

Power inductors arent designed for 400KHZ so cook quickly.

3 amps shouldnt be a problem for class d inductors, you should find one ok.
Have you tried coilcraft ?
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Old 5th May 2011, 03:08 AM   #10
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what is a class D inductor? is there some sort of spec? I just see current ratings
and Q @ ___ kHz

Maybe I will just buy a high current LC filter, they list thier cut-offs so im sure if it says 3 A with a 1 MHz cutoff I can use it.
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