> > It is unlikely that you could build an IC based switching
> > regulator for a component cost much cheaper than for
> > this one.
> .
>
>  Not cheaper (LM3485 is $.50 1K+), but
> nevertheless, interesting. From LM3485 d
> atasheet:
> 4.5V to 35V wide input range
> 1.242V to VIN adjustable output range
> High Efficiency 93%
> Maximum operating frequency > 1MHz


Nice looking IC
Details here         http://www.national.com/pf/LM/LM3485.html
Uses the FET Rdson as the current sense resistor which is a good trick.

Uses a PFET which is less fortunate but you can't have everything. Couple
this with eg a MDT2955 FET at about $US0.35 each ($NZ0.76 when I priced them
locally earlier today) in tube quantities and you have a substantial power
down-converter

FET         http://www.onsemi.com/productSummary/0,4317,MTD2955V,00.html

Note the LM3485 costs $22 one off from  NatSemi - they don't really want you
to buy small quantities.


        RM

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