I am looking to PWM a 15W LED array with a 11V drop voltage. I found a tutorial on building a constant current supply (specifically, Step 8 @ http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/) using the FQP50N06L, and I was wondering:
Is there any particular reason why I never see the MOSFET between the cathode of the LED and Vin? Assuming a Vin of 12V, and a 5V logic signal, should I expect the MOSFET to not conduct from drain to source? Is this why the switch is typically located between the anode and ground, after the load does its business?
Seems trivial, though I never thought the sequence of components in series mattered.