[sdiy] Cap heads-up

[Neil Johnson]

Hi,

ezion wrote:
> It has been a few months since I last looked at high value (SMD) ceramics
> but...
> High value ceramics de-rate with applied voltage, often the
> capacitance goes down rather quickly.
> Think 5 to 20% of the capacitance left @ half the maximum voltage.
> And some models show quite prominent dielectric hysteresis.

It depends on the dielectric:

Y5V is terrible for this behaviour - as you say they can lose around
80% of their rated capacitance at full rated voltage, but it is a very
cheap dielectric material, so its worth throwing it at a decoupling
problem.

X7R is much better, about +/-10% or so over the rated voltage.
Although it still suffers from ageing effects.

C0G/NP0 is very, very stable (some manufacturers call it "ultra
stable") - it is not affected by applied voltage or ageing effects at
all (i.e., below typical measurements).

Cheers,
Neil
-- 
http://www.njohnson.co.uk