Power Supply Filter Capacitor Size

[Grant Richter]

> 
> Two questions I have, does the regulator have to work harder if it's
> input voltage is highly modulated?  Is it important/desirable to have
> low input ripple voltages to the regulator for any reason?
> 

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.

For ultra critical linear systems it is common to sub-regulate
the critical system. Say +/-15 volts for the main system with
+\-12 volt low power sub-regulators for a preamplifier stage.
That gives twice the ripple rejection.