> *>Given that I have a 'wish' for a fixed current output, how
> *>about using an SMPS as a current regulator?
>
> Ok for your scheme.
>
> *>I know it is not going to be looking for a peak but I am
> *>not sure I understand how MPPT would work with this setup?
>
> It would not. Forget mppt if you want constant current out.

Without MPPT or something more than just "turn up the switching regulator
when the output current is low", the thing will collapse the first time
the solar panel can't quite keep up with the energy demand.  As long as
the panel has excess capacity, no problem.  The switching regulator will
appear like a lighter load than that which drains maximum power from the
panel.  In other words, the panel voltage will be higher than the maximum
power point for the given illumination.

Now think what happens as the illumination decreases but the output
current demand remains constant.  The switching regulator will present
more and more of a load until the panel is operating at the maximum power
point.  As soon as that point is reached and the illumination dims a
little more, there will be a runaway effect.  The switching regulator
wants more power, so it presents a greater load to the panel.  This drops
the voltage below the maximum power point, giving the regulator less input
power, which it tries to compensate for by increasing the load, etc, etc.
Very quickly you end up with the panel at maximum current and no voltage,
and therefore producing no power.  It won't even be able to recover when
illumination rises.  Oops.


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