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designing around the MC34063 min inductor value formula

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Simon:
oh right ? so what do they call MPPT controller chips ? how do i recognise one ? my plan was to use a cheap SMPS controller with some nice low Rdson mosfet(s) that had an MCU supplying the feedback signal taking it's cue from a current sense chip (MAX4080). I'd just write a simple program that sends a PWM signal that is low pass filtered to the SMPS controller feedback and varies (dither's) it in order to stay around the maximum current output

scrat:
The way you describe it is one of the standard ways to implement an MPPT control.
A PWM controller is not an MPPT controller, it simply gives out a PWM modulated signal based on the reference you give it.
Although I think there could be some exotic MPPT controller ICs, somewhere, I think the solution using an MCU is the simplest and cheapest.
You can run a relatively slow MPPT algorithm on the MCU, then you have two alternatives: output the current reference to an external PWM current controller (something like UC2886) via filtered PWM or an external DAC, or take the current control inside the MCU, too. Implementing a good current control inside the MCU usually requires high processing speed, but you could accept a low bandwidth control and update the duty-cycle at each n PWM cycles, while using hardware current protection (comparator).

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