efficiency dropped away after 1A input. What was the input V
Well done first attempt... see it does work and it is easy.
Either your flimsy wiring was absorbing the extra input current, or your inductor efficiency fell off.
I don't know which, but i assume that with your low freq, more turns on the inductor and airgap testing may be the key here.
Quick experiment will show the way.
Check the air gap as this will saturate at higher currents, and not give you any return on the output voltage.
So.
1 Fiddle the airgap and note the difference.
2 throw on some more turns and note the difference.
Not very scientific I know but from here it the best I can do.
The inductor is the key to output i have found. My setup is not ideal, but it works. You will do well to invest time into testing every whichway with the inductor and airgap as that is the key to your efficiency over the range.
A lousy inductor works efficiently for a very small current, then falls away as you pour the juice on.
A good inductor works well for the small current, but keeps the faith for larger currents as well. Eventually you will saturate any inductor, but it's all in the coil.
have you checked the wave form across the fet yet.. Is is nice and square?
If the fets are staying dead cold at these currents, the wave form must be good. At 3A with poor waveform, heat will turn up very quickly.
Once again, well done, will this solve your stepup problem?
.................oztules