>
>   You can't use one resistor from 10V to 80V input voltage variation !
>You need a high voltage current source ( one pnp + one npn which will
>dissipate indeed about 1.5W, this sort of current source are used to
>supply from 24 to 240V ac or dc any low current boards ) You don't need
>any linear reg. A zenner is enough. But you'll have some thermal stress
>there...
>Vasile

You're right, I was thinking that, but I wrote resistor. :)
The resistor version would be much toastier.

I've done this in similar situations with two transistors, configured as a
two terminal constant current source. Set it not much above your maximum
current demand, and it will dump the excess into the zener, and everyone's
relatively happy.

The pass transistor should probably be one designed for TV video output
stages.
They will be cheap and robust.

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