Lpc2000

What type of efficiency does a linear regulator give you when setup in a 
switching-style topology for low currents?

Check out L7805C datasheet figure 27 in case you don't know what I'm 
talking about.

While we're on offtopic, what diodes do you guys recommend using, 
especially for lithium backup purposes?  Most diodes that I see that are 
frequently used have large forward voltage drops for any non-trivial 
current draw.

-- Sean

At 12:50 PM 12/2/2005, Guillermo Prandi wrote:
>Thanks, Joel. Efficiency on those chips seems still very low (around
>50% for my circuit's average load, 15 mA), though the low quiescent
>current seems tempting.
>
>Guille
>
>--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
> >
> > Guille wrote,
> >
> > > Hi! I am in trouble trying to find a voltage regulator suitable
>for my
> > > project; my project features an LPC2138, a GPS and a radiomodem.
>When
> > > idle, it draws around 20-25 mA from the 3.3V source, 500 mA when
> > > working hard and with short (50 mS) peaks of up to 1.8A. The
>supply is
> > > a lead-acid 12V battery (can't change that), and occasionally,
>when the
> > > battery is charging, the input voltage will rise up to ~20V. The
> > > problem is the regulator efficiency. We were going for the LM2676-
>3.3V
> > > switching regulator, because it seemed simple and in range, but
>two
> > > things made it a poor choice: it draws about 4.3 mA from the
>battery
> > > just for its own supply, and its efficiency when the load is in
>the 20-
> > > 25 mA range is awful (less than 50%, not counting Iquiescent). I
>looked
> > > everywhere but I couldn't find any other switcher with better
> > > performance in these conditions (12V in, 3.3V out, 20-25 mA
>average
> > > load, but >1.5A capability). And there's a catch! The radiomodem
>is
> > > extremely sensitive to VCC getting lower than 3.3V especially in
>the
> > > current peaks! Also, it should be relatively easy to find in ~400
> > > quantities (i.e., Digikey, Mouser or your suggestion).
> >
> > I've used the MAX5035 for automotive apps.  Nice part.
> > <http://www.maxim->http://www.maxim-
>ic.com/solutions/automotive/parts.mvp/scpk/1458/pl_pk/0
> >
> > You might consider the MAX5090, it goes up to 2A.  The input
>voltage range
> > is 6.5V to 72V.
> >
> > Joel
> >
>
>
>
>
>
>
>
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