How to choos decoupling capacitor sizes

[atpham89]

How does one choose the correct decoupling sizes for their system?

My setup is:

There is a AC to DC Power source that supplies 12Vdc with 1.25A.

The source is then fed to a solid state relay and PWM Proportional Valve Driver in parallel.

How would one know what size of a capcitor to use? And is the placement of the decoupling capacitors positioned as close to the Vsource as possible?

Thanks.

 

[ho83]

it depends on the ac/dc converter and the load, any way if the ac/dc converter is a full wave rectifier try this:

C=(I*T)/(2*Vripple)

C : is the capacitance
I : is the maximum load current
Vripple : peak-to-peak ripple voltage
T : the period of the ac voltage


finally the capacitors is perferred to be near the load.

 

[artem]

depends on power noise and current timing for consumption circuit and also frequency of current consumption.
for high freq pay attention to capacitor inductance which is high for MLCC capacitors , (some low caps connected in parallel to high capacitance caps).
To decrease the inductance of caps multiple parallel connected caps are used as well .
Current path through ground for caps should also be controlled.