Ignore "high voltage circuit" is not used.
It's a prototype built in a breadboard with jumpers, and i have a problem with the mosfet "IRL540N", is not passing the optimal current and spark gap must be very close with almost no gap. When using power directly without a mosfet spark is very powerfull (see "SPARK-SW"), noisy and big gap, but the mosfet cut all the potential. I'm using a full charged lithium battery at 4.0V on MCU side, also i tried with 5V power supply and i get the same result (very weak spark). Transformer pull 3A max of current when connected properly. I also tried with other TTL mosfet (same result).
Looking at datasheet the IRL540N should work good even with 2.5V for that current (3A), but in fact is not.
Additionaly i have used a 16A relay to troubleshoot the circuit, i activate the relay with the 7.4V power supply and the mosfet and it works well, pulling 2A (maybe because of weak jumper cables). Still i don't want to use the relay, it consumes 30mA and as the voltage drop on batteries relay may not work good.
More images: https://dl.dropboxusercontent.com/u/18602178/IMG_20160612_224111.jpg https://dl.dropboxusercontent.com/u/18602178/IMG_20160612_224120.jpg https://dl.dropboxusercontent.com/u/18602178/IMG_20160612_230414.jpg
What can cause that problem?