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How to choos decoupling capacitor sizes

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atpham89

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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.
 

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.
 

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.
 

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