You seem to be assuming that the current regulator has to be linear. That's
not the case at all - straightforward to have a switching current regulator,
in which case you don't have a problem with heat. Given 80% efficiency
(which isn't hard to achieve) your maximum power dissipation in the
regulator is only 2W when the output's 10V and 800mA - much simpler than a 2
stage process.

On 3/10/07, Vasile Surducan <piclist9@gmail.com> wrote:
>
> 5V and 10V at 800mA is not the same.  Keeping dissipation small on
> the current regulator is the key. Definitely I'll vote for an 170VDC
> to 6VDC converter followed by a constant current generator. Power
> dissipation will be maximum (6V-2V)*0.8=3.2W and minimum
> (6V-5V)*0.8A=0.8W. More power at 10V load voltage swing.
>
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