On 08/31/2011 09:02 PM, jongkung01 wrote:
> Hi experts,
> With all the talk about ESR, I was thinking, can you use multiple capacitors in parallel to build a low ESR capacitor? Is there a reason why this might NOT work ?
> I only ask because I never see this config (or I hardly see this config). The few times I saw parallel capacitor, I don't think it was to lower the ESR.
> Am I crazy ? :-(
This trick is done on almost every computer motherboard in
existence. Those buck converters than change 5 volts or 12
volts to 1.5 to 3.3 volts at many amperes often have 6 to 10
capacitors in parallel to get a low enough ESR and series
inductance. They often have extra spots for more caps that
testing showed they didn't need, when the capacitors were
new. I wish the holes were not filled with solder, to make
it easier to add in those extra capacitors.
When I got the motherboard in the computer I am using to
write this email, instead of adding more paralleled
electrolytics in those extra holes, I added a 4.7uF 25V X5R
SMD capacitor across the end of each of those electrolytics,
to bypass the highest frequencies of that ripple current
around them, to lower their internal temperature rise and
make them last longer and to improve the operation of the
I did the same thing for the electrolytics in the output
side of the power supply, except that I stacked 4 of those
caps on each electrolytic. The ones that benefit the most
are the ones connected directly to the rectifiers because
they have the highest frequency components in their pulse
currents. The ones after the low value filter inductors
that are right across the supply outputs do not see such
sharp current pulses, but see ripple current from the loads.