Hmm, are your sure you interpreted figure 2 (http://www.irf.com/product-info/datasheets/data/irf9540n.pdf) correctly? It's the first time in my life that I try to read a diagram like this, but it seems to me that the IRF9540 drops 1V at 2A. In the case of the LED cube one IRF9540 handles 64 LEDs, which means that the current going through it ranges from 0.02A (1 LED lit up) to 1.28A (64 LEDs lit up). The way I read this figure 2, at 0.02A the voltage drop is 0 but I can't figure out from the diagram how much the voltage drop is at 1.28A... I don't really understand it, but can I really use 1V as voltage drop across the IRF9540 regardless how much current (0.02A to 1.28A) is passing through it?
Thanks,
Andras