Thanks, this sepic has been built and is working well.
I am just wondering now though, the design appears excellent, as no electrolytics were needed...the input capacitance is 66uF total, but because its always less then 9V input, these are just 16V rated ceramics.
It seems to be the perfect converter, not saddled with the instability worries of a sepic, and not needing any output capacitance, let alone electrolytic output capacitance.
As far is the control loop is concerned, the converter might just as wel be a boost converter....it doesnt care.
It appears that regulating the input current gives this great advantage in terms of stability , and i mean stability obtainable even with no output capacitance.....that is excellent, because usually one has to have big 'lytic cans to ensure stability.