Basic question about cap's

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KamPutty
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Basic question about cap's

Post by KamPutty » Thu Nov 02, 2006 11:22 am

Hi all,

I have a circuit that calls for a 250uf cap, and a 0.05uf cap. I own none of these so I need to purchase. Now.....looking around, I can find a 0.05uf cap thats $1.40 per!!! Rated at 1000v. But there is a 0.047uf rated at 50v for $0.09 per (more like it!), and I cannot find a 250uf.

Quesiton, can I use the 0.047uf instead of the 0.05uf? and what if I cannot find the 250uf? Can I use the 220uf?

Since they are rated +-10~20%, they would overlap....yes?

This is for a low voltage setup...hooking up a LM386 with gain = 20

Thanks!

~Kam (^8*

rshayes
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Post by rshayes » Thu Nov 02, 2006 1:51 pm

That sounds like an old circuit. Most recent parts use the standard values.

The LM386 normally operates on less than 12 volts. Capacitors with a voltage rating greater than this will be good enough.

The 250 uF capacitor is an electrolytic capacitor. These are not made to very tight tolerances, and are not very stable. A 220 uF capacitor would be an acceptable substitute for this part, and, since this is a standard value, should be easy to find. I would look for a 220 uF 25 volt part. A higher voltage rating is also acceptable, but the capacitor will be slightly larger.

In this application, the .05 uF capacitor is probably a coupling or feedback compensation capacitor. Again, these appplications do not require tight tolerances. A .047 uF capacitor should be acceptable. This could be either a ceramic or plastic film capacitor. The ceramic capacitor will probably be smaller and cheaper. These are rare and somewhat expensive in low voltage ratings. I would expect that a part rated at 50 to 100 volts would be the least expensive.

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Chris Smith
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Post by Chris Smith » Thu Nov 02, 2006 2:31 pm

Remember the rule of thumb for caps. Huge variance in all caps.

We were ruled by a + 25% and - 50% and had no problems.

Generally a 10% +&- difference works very well in almost all situations.

dyarker
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Post by dyarker » Sat Nov 04, 2006 4:28 am

"... by a + 25% and - 50% ..."

Very good, except it was -25% and +50%. Now aluminum electrolytics are -20% +80%, -10% +50% or ±20%.

Perfectly logical and even helpful while moon was less than half full. Total random insult mode starts today. :lol:
Dale Y

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Chris Smith
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Post by Chris Smith » Sat Nov 04, 2006 8:47 am

Thank you for your sleeping pill, you know exactly what assumption means. ZZZZZZ

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philba
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Post by philba » Sat Nov 04, 2006 9:09 am

dyarker wrote:Perfectly logical and even helpful while moon was less than half full. Total random insult mode starts today. :lol:
you sure called that one right

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Dave Dixon
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Post by Dave Dixon » Mon Nov 06, 2006 7:16 am

Chris Smith replies << Thanks Dyarker, you were right. Kudos. >>
Yeah, I'm just dreaming.

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Chris Smith
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Post by Chris Smith » Mon Nov 06, 2006 9:42 am

The sheep huddle closer today, what’s new. Must be exciting?

Small minds have nothing to actually do. ZZZZZZ

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