Re: gEDA-user: Switching regulator question

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

On Mon, Jun 18, 2007 at 10:46:31AM -0700, Steven Michalske wrote:
> Putting a LC filter on the output of the bridge rectifier will help  
> you out.

I looked briefly at LC filters to handle 120Hz ripple.  Requires some
pretty large, expensive inductors if I'm not mistaken.  Seems cheaper
in both board space and money to have more capacitance.


> Be careful with over sizing switching power supplies,  what is the  
> minimum operating current of your design?

My understanding is that with low currents that switcher will enter
discontinuous mode (where inductor current goes to zero at the end of
each cycle), and this will cause higher output ripple at the switching
frequency and more overshoot on the voltage.  This is not a big
problem in my application.  Is there something else that I need to be
aware of?

I haven't calculated minimum current, but I'm guessing 50mA.  (Peak is
around 350mA, designing for 1.5A. so that's a big range.)


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