regarding capacitor value calculation in power supplies

ericgibbs

Joined Jan 29, 2010
9,768
hi 24,
Welcome to AAC.
In order to calculate the required capacitor values for a power supply, you need to specify the design current/voltage specification of the PSU also the permissible voltage ripple etc ...

Do you have a PSU design specification, post an example.

E
 

Thread Starter

yahooamit24

Joined Mar 12, 2020
8
Thanks for your support ,
yeah psu requirement is 3.3v , 500 mA . I know the working voltage should be at least 1.3 times of requirement but don't know the capacitance .if you have any standard method for this pls let me know.
 

ericgibbs

Joined Jan 29, 2010
9,768
hi.
For a 3.3Vdc supply at 0.5A.
You could use a AMS1117 3.3V 800mA series type regulator.
Do you have a mains step down transformer that you want to use, say 5Vac output or so rated at 10VA.?

E
 

Hymie

Joined Mar 30, 2018
797
The discharge rate of a capacitor is given by V = ( I x t)/C
Where
V is the capacitor volt drop
I is the capacitor discharge current
t is the time
C is the capacitance value in Farads
As an example, a full wave rectified voltage (at 50Hz) from a 12V transformer secondary with a constant current discharge of 500mA and a reservoir capacitor of 4,700µF would have a peak voltage of 12 x 1.414 = 17V. Over 10ms the V drop = (0.5 x 0.01)/0.0047 = 1.06V.
Note the above calculations ignore any bridge rectifier diode voltage drop.
 
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