When should filter cap tolerance be small and when does it not matter and you can have say a 20% tolerance for a filter cap? Is there a rule such as in general, the smaller capacitance the filter cap is, the tighter tolerance it needs to be?
In theory, yes. You add capacitors in parallel.But doesn't adding caps in parallel equate to a single cap with value equal to the sum of the values? then the largest value cap will dominate the filter and appear as a near-short at the high frequencies and negate any significant contribution by the lower value parallel caps? i have seen such parallel cap filters added in circuits and schematics, but it looks to me that they fail to actually perform the assumed filter action. Current takes the path of least impedance.
A typical tolerance for electrolytic capacitors is -20%/+80%. If you design assuming values are 20% less than nominal, you won't have problems.When should filter cap tolerance be small and when does it not matter and you can have say a 20% tolerance for a filter cap? Is there a rule such as in general, the smaller capacitance the filter cap is, the tighter tolerance it needs to be?
by Jake Hertz
by Robert Keim
by Jake Hertz