>I seem to quite often need to run a "voltage present" LED 
>on a very wide
> range of voltages...  For instance, in one case the input 
> voltage can
> run from 5 to 60VDC, or more.

> I'm hoping I can find something just marginally more 
> expensive than
> putting a current limiting resistor in place.   Is there 
> some magic
> circuit I've missed...

Here is Richard Prosser's version of "my" G.S.R.* switching 
regulator.
D8 may not be needed.
Despite apparent high parts count it can be very small and 
cheap.

        http://others.servebeer.com/misc/gsr_rp.gif

Roman Black's "Black Regulator" is perhaps slightly cheaper.
While it has poorer regulation it may well be adequate for 
your needs.

I have had a version of this operating  from 12V to 200 V 
in.

Here is an independently developed version which is 
essentially identical.

        http://sound.westhost.com//appnotes/an006.htm

A simple change to a constant current output drive (suited 
to LED use) is seen here

        http://sound.westhost.com//appnotes/an003.htm

If a P Channel MOSFET is used for the high side switch 
remember to zener clamp the gate to avoid death at higher 
Vin's.

This is a "hysteretic converter". Operation as shown is 
marvellously chaotic. Operating frequency and PWM ratio 
varies vastly, which allows it to achieve the vast max:min 
Vinput ratios that it does. Hysteresis DOS exist despite 
some refusing to believe it. Clue: Ripple on output cap is 
an essential part of the operation. Adding a series RC 
(location left to the student) will provide extra and more 
normal hysteresis and a more determinate waveform. MAY help 
efficiency somewhat.

For an IC solution a MC34063 would be cheap and goodish. 
Vinmax = 40V so a cheap external transistor probably 
required for drive.



        Russell


GSR = God's Switching Regulator.
Story offlist on request.














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