I have a working project where I am using an ULN2003 darlington array to power an RGB LED strip.I want to expand to a bigger strip and have therefore bought some MOSFETs from sparkfun as these could be controlled directly from a microcontroller...Linking to the actual mosfet you brought would be useful to try an answer your questions. Are they logic level mosfets?I have seen a few projects with MOSFETs, and some use transistors to drive the gate. Some use pull-up resistors and some use resistors to protect the mosfet. Now I'm not sure what I need. I thought this was just replace the darlington with the MOSFET Depends on if you are using a logic level mosfet or not. pull down resistor is useful for safety purpose in cases where the externally controlled device is powered up but the arduino is power off. series resistor from arduino to gate is for output current pin protection during charging and discharging the gate capacitance. Again it depends on the specifc mosfet you are using how important that might be. 300 ohm series resistor is a good compromize.Looking for some advice How to wire it all up. I have 12v supply voltage and 5v from the arduino board, also using the PWM outputs on arduino.Your best bet is to draw something up and post it and then we will punch holes in it.
This is a "logic gate level" device.. I think you'd have no problem just driving it like the Darlington you had, up to 5 Amps output or so.A 10K input Gate-to-Source pulldown and a 220 ohm series resistor from Arduino pins would be nice conservative design.. Modern Power FETs are So nice!