Best way to PWM multiple LED strips

I’m trying to PWM four sets of LED strips using and Arduino Mega r3. led strips are 100 led per strip 12v I have a MOSFET and npn transistor sitting here but just can’t seem to get it to work. There seems to be a constant current through the circuit. The led light and fad just barely. I need to fade from off to full on. Any help?.

Hello. Have you tried some of the suggestions, particularly #15, on this link?


And you'll have to show exactly what you have tried and tell us exactly what transistor and MOSFET and what current the strips need and what power supply and how you've hooked everything together...