Power Supply design

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It looks like the fomula's I have found online for fiquaring out what size cap to use are pretty involved. One thing - they ask the acceptable ripple after the cap? How do you know this? It is going into the lm317, so I assume this is the ripple IT can accept?

 
ripgtr said:
It looks like the fomula's I have found online for fiquaring out what size cap to use are pretty involved. One thing - they ask the acceptable ripple after the cap? How do you know this? It is going into the lm317, so I assume this is the ripple IT can accept?
The ripple the regulators can accept is governed by the max input voltage (37Vd and the minimum that is necessary for the reg to operate, that is about Vreg + 3V. So you have to know the ac voltage your xfmr produces, at the rated current. Then you have to know the current draw. The ripple voltage for a single-wave is I.T/C
T being 20ms for 50Hz, 16.6ms for 60Hz. Example: 100mAmpdc with 1000uF gives 2V ripple
Full-wave is about half than single-wave. You would need only half the capacitance for the same ripple.
 

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