> how would you go about making a 4.5V supply from batteries ?

Deep ends on what constraints are important to you.

For N cells with minimum allowable voltage and an LDO regulator

(Vcell_min x N) - Vldo_do =3D Vsupply

If Vldo_min is 0.2V then you need 4 x Alkaline (1.5 V+ to 1.2V per
cell) or 5 Alkalines (1.5V to 0.94 V)
First wastes bottom end capacity and second wastes top end.

NimH not vastly better. 5 as above.
4 too few. 6 allows very low Vend but not good for cells.

Some form of boost or buck converter makes sense.


          Russell

> I'm evaluating the rfPIC and find that Microchip, for some reason,
> has reduced Vdd and Vddrf from 5V to 4.5V max. I was hoping
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