Samuel said:

Typo - should read "1 mF" or "1000 uF"...

The filter will sit right after the rectifier and in front of the

regulator (IC & ext. transistors). Goal of the CLC-filter would be

lowest ripple for C=1 mF.

Samuel

I have not seen a linear regulator that likes to be fed with an

inductance, so I think your choices are CLC or LC or C. The first and

last (capacitive input) tend to charge the caps up to the peak voltage

of the rectified AC somewhere approaching 1.4 times the AC voltage of

the secondary, while the LC (inductor input) tends to average the

rectifier output. This averaging effect only takes place if the

inductor current is continuous throughout the rectification cycle. So

for light loads or insufficient inductance, the voltage will rise.

Indictor input filters are good if the transformer voltage is a bit

too high, and they also spread the diode conduction time throughout

the cycle, lowering the transformer copper losses, line harmonics and

diode peak current. The CLC (pi) filter) doesn't put much AC voltage

across the inductor, so can work with smaller inductance. You just

want ot avoid having a resonance at any rectified line harmonics, so

the fundamental resonance should be lower than the second line

harmonic (the fundamental of the rectified line). But in all cases,

more inductance implies lower ripple, so your design goal of minimum

ripple still implies infinite inductance. By the way, what is the

load that you are so worried about rectifier filtration, if you have a

linear regulator? after the filter? The output ripple will be

dependent on both the filter and the regulator, assuming the filter

ripple is not so deep that the regulator has nothing ot discard at the

minimum points on the ripple.

What is the secondary voltage from the transformer you are using to

drive the 30 volt 4 amp linear regulator?