[R-390] Power supply capacitors

[Tim Shoppa]

VE3EOS writes:
>  A bigger capacitor gives a higher 
> minimum voltage (less ripple) but the extra energy just shows up as
> heat in the regulator.  Bigger capacity also increases the inrush 
> current - the diodes only conduct for a short time so the instantaneous
> transformer current  is a lot larger than the average DC load current.

Not just at start-up, but all the time, if a guy puts in too much capacitance.
I-squared-R losses in the transformer go up and up and up because
the peak current goes up and up as the capacitance goes up and up
the conduction angle becomes smaller and smaller.

As the peak current goes up and up the RFI generated by the 120Hz
switching will go up and up too. Not a problem if good circuit layout
with no big loops are used... but a neophyte (e.g. the guys who use
filter capactors that are way too big) will often lay out a
circuit with enormous loops.

Tim.