LM2575 datasheet says: "For an input voltage of 12V or more, the maximum available output current in this configuration is approximately 0.35A. At lighter loads, the minimum input voltage required drops to approximately 4.7V". So it seems a higher input voltage should work better (like 19V from laptop supply).
And: "the output capacitor values must be larger than what is normally required for buck designs. Low input voltages or high output currents require a large value output capacitor (in the thousands of micro Farads)".
And: "The recommended range of inductor values for the buck-boost design is between 68 μH and 220 μH". So:
(..) and a bigger coil(i dont know the value
)
Doesn't cut it, and I'd
guess this might be your problem. Amperage is something you could estimate (or feel if coil gets hot), but you
have to know what inductance value you're working with. If the value is too high, then the coil takes too long to respond to voltage changes. If the value is too low, in the time the coil is switched on, current rises above maximum, the 'inductive resistance'
falls away & current rises faster still. In effect, a short circuit. At which point surrounding parts are
very easily fried.
You sure the diode & LM2575 are still okay?
Also what confuses me is that the same materials for the +5v dc converter works pretty good.
Well it's a step-down regulator, not an inverting one. So you can
use it as such, but it was designed for another job.