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...
(https://i.imgur.com/K5utyAl.png)
A plethora of 100n caps to use up?
dave
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.
Quote from: madbean on May 21, 2020, 01:06:41 AM
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!
Quote from: madbean on May 21, 2020, 01:06:41 AM
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
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
Ok, that may have actually made it thru my thick head this time. Thanks for the explanations guys!
Quote from: Aentons on May 21, 2020, 02:29:26 AM
Quote from: madbean on May 21, 2020, 01:06:41 AM
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.
Well that's my best offering.