Quote Originally Posted by docwisdom
...Its quite a large unit, but that is to be expected for 60w...
Well, it is even more, it provides a stable 12V output at Input Voltages between 8 and 18 Volts, so it steps up or down at high current (with high efficiency).

Quote Originally Posted by docwisdom
Anyway, could you or anyone else recommend component changes so I can operate from a 4.5 to 7.6 output at 3A?
Again there are many ways, of course you can simplify the circuit as you don't need to step up, all you need is a "simple" step down switching regulator.
(Your minimum Input voltage is always higher than the maximum required output voltage)

See the UC3843 Datasheet for design examples.

Quote Originally Posted by docwisdom
p.s. What is your opinion on switching regulators like the LM2676/2678? Both you & Steve mentioned that they are expensive, but digi-key lists them around $6 each. They are available in variable output versions as well.
Sure, you could even use an LM2676, that would save some components like the external MOSFET.

I'm using the 2676 in one of my (GSM) designs where part count and PCB space was an issue, but overall this design was more expensive than others.
However, the 2676 is a somewhat expensive but reliable component.

And as mentioned earlier:
if you want efficiency, take special care of the inductors and capacitors you use!

You'll be surprised what increase (or decrease) in efficiency you get by simply changing a capacitor or inductor.

I have spent days with winding my own inductors on different cores to get maximum efficiency over the full Input voltage and output current range.