[time-nuts] Low noise power supplies - dont' use Electrolytics

[Poul-Henning Kamp]

In message <CABbxVHvNSAxBx5uOrjTQeSTTd50yEDyAVkGXh52bPsPUAYtyWw at mail.gmail.com>
, Chris Albertson writes:

>One question:  How does one avoid using electrolytic caps if you need
>(say) 1,000uF or even 100uF.   Those would be some mighty big film caps.

One detail, often overlooked, is that electrolytics seldom are
dimensioned very precisely, mostly because they do come with such
big capacity but also because them have very big tolerances, +/-
50% is not uncommon.

Another effect that causes overdimensioning is that they are not very
good capacitors, in particular at higher frequency.

I have in a couple of instances replaced electrolytics with film-caps
and gotten away with less than 1% of the original capacitance by doing
a bit of calculations and measurements on the actual circuit.

In one case, an audio circuit had 1000uF for a handful of opamps,
using 4.7uF of good film capacitors instead reduced THD by 80%.

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