Power Supply Filter Capacitor Size

[Christian Hofmann]

On Wed, 08 Dec 1999 20:14:30 +1100
Paul Perry <pfperry at melbpc.org.au> wrote:

> At 11:45 PM 7/12/99 -0600, Grant Richter wrote:
> >
> >Regulator power dissipation (read heat) is reduced by matching
> >the capacitor to the load. The regulator does not have to dissipate
> >the constant excess input voltage and as log as the bottom
> >of the "ripple" is above the dropout voltage, it should show the
> >power supply ripple rejection the regulator is rated for.
> >
> .....can this be true?
> The dissipation in the regulator is the drop across the regulator,
> multiplied by the current through it.
> I mean, this is Ohms law in practice.
> 
> For a normal three terminal regulator, ther is no such thing as 
> matching the capacitor to the load, provided it is big enough, as
> pointed out by the earlier posts.

Well, I think the proper wording should be "power dissipation _can_ be
reduced". 
I guess what Grant meant was: By reducing the ripple (increasing the cap
value) the xfmr voltage can be reduced without reaching the regulator's
required min input voltage at each ripple period.

cu
Christian