Author Topic: power filtering in Vfe two 100n caps parrallel?  (Read 256 times)

cooder

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power filtering in Vfe two 100n caps parrallel?
« on: May 20, 2020, 04:48:03 PM »
I have seen this now in several schematics of Vfe designs, having two 100n caps parralel to ground for power filtering.
What's the point of that, what benefit would that have for example in comparison to put a single 220n cap to ground there?
I'm sure Peter was thinking of something there... he's that clever sorta guy...

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davent

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #1 on: May 20, 2020, 06:10:59 PM »
A plethora of 100n caps to use up?
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madbean

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #2 on: May 20, 2020, 07:06:41 PM »
The small power filtering caps are placed directly next to the individual ICs (usually as close to the ICs power pin as possible). It's not totally necessary but it is good practice for filtering/noise. Actually, on many of the dual supply effects he puts two: one for positive and one for negative supply of each IC.
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cooder

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #3 on: May 20, 2020, 08:19:52 PM »
The small power filtering caps are placed directly next to the individual ICs (usually as close to the ICs power pin as possible). It's not totally necessary but it is good practice for filtering/noise. Actually, on many of the dual supply effects he puts two: one for positive and one for negative supply of each IC.
Awesome, thanks for the quick illumination!
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Aentons

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #4 on: May 20, 2020, 08:29:26 PM »
The small power filtering caps are placed directly next to the individual ICs (usually as close to the ICs power pin as possible). It's not totally necessary but it is good practice for filtering/noise. Actually, on many of the dual supply effects he puts two: one for positive and one for negative supply of each IC.
But why the multiple caps in parallel? I thought I read somewhere that it helps smooth the ripples. Does that sound right? Sometimes I'll see 4 or 5 in parallel

davent

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #5 on: May 20, 2020, 08:57:56 PM »
Each cap is physically situated on the pcb at the IC pin it's filtering, two IC's, two caps in parallel on the schematic... haven't seen the rest of the schematic or pcb.
dave
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Aentons

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #6 on: May 20, 2020, 09:04:36 PM »
Ok, that may have actually made it thru my thick head this time. Thanks for the explanations guys!

madbean

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Re: power filtering in Vfe two 100n caps parrallel?
« Reply #7 on: May 20, 2020, 09:18:35 PM »
The small power filtering caps are placed directly next to the individual ICs (usually as close to the ICs power pin as possible). It's not totally necessary but it is good practice for filtering/noise. Actually, on many of the dual supply effects he puts two: one for positive and one for negative supply of each IC.
But why the multiple caps in parallel? I thought I read somewhere that it helps smooth the ripples. Does that sound right? Sometimes I'll see 4 or 5 in parallel

Here's one reason: ICs used as amplifiers. The smoothest action of amplification requires minimal DC ripple. Placing decoupling caps in proximity to the amplification device ensures the lowest DC ripple one can obtain from a given supply because of the inherent parasitic capacitance (and maybe ESR?) of circuit boards. The fact that caps in parallel have additive capacitance is just a consequence.

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« Last Edit: May 20, 2020, 09:31:17 PM by madbean »
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