Alan,
another option is a Cuk style buck supply that varies output duty cycle =

as an inverse square of switch duty cycle. Should get efficiencies of 70 =

to 80%. I'm not sure where you can find details other than a paper from =

IEEE in about 1995. I can find the reference if you want. I photocopied =

it from the school library so I don't have any computer refs.
--
Martin Klingensmith

alan smith wrote:
> Came across this design, even better than the ON Semi that still requires=
 a transformer.
>    =

>   http://www.supertex.com/pdf/datasheets/SR08x.pdf
>    =

>   You can get a regulated 3.3V or 5V @60mA, plus an adjustable 9-50VDC  1=
00mA(adjustable using a divider network to a feedback pin) output.  Downsid=
e is its only 55% efficient, but for the size its not bad.  And I think...i=
s a bit better than just the LC type supplies, not as cheap but perhaps mor=
e robust.
>    =

>   Anyone care to comment...good and bad on this app note?
>    =

>   My only issue is I need 5V and 3.3V so looks like the 9V gets dropped u=
sing either an LDO or small switcher.  I need 50mA at 3.3V, and 30mA at 5V
>    =

>   -Al
>
>  		=

> ---------------------------------
> Talk is cheap. Use Yahoo! Messenger to make PC-to-Phone calls.  Great rat=
es starting at 1=A2/min.
>   =

-- =

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