Re: gEDA-user: Switching regulator question

[DJ Delorie <dj@xxxxxxxxxxx>]

> Doesn't seem that you gain or loose anything here - assuming the
> switching time is not affected.

The FET helps because there's an ohmic loss across the diode on the
order of Io*Vf when the switcher is in the off state.  The FET has a
lower Von (Vf) than the diode, which reduces this particular loss.

You still need the diode, though, in case there's current during the
transitions.

> The trick is to make sure the lead + track inductance to each cap
> looks similar (else the nearest one to the switch will fail first).

The board was limited by physical spaces, so I just used really big
tracks.  Plus I put a bypass cap right at the switcher.  Some
switchers have EMI suggestions for input, too.

> 105 degree rated caps are often worse on ESR, so in some
> applications will run hotter. I read somewhere that its best to use
> 85 degree caps unless the heat is imposed _on_ the caps (rather than
> from internal dissipation).

And choosing caps with higher voltage ratings helps them last longer,
too.


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