Will this circuit work to switch LED lamps on and off on a motorcycle? I was hoping to build a simple circuit to control some lights on my bike, but since most accessories for cars and other vehicles are directly connected to ground I need to switch on the high side. I plan to use ULN2003 darlington array to control 5 P channel mosfet, probably Infineon AUIRF6215. At the moment there is no plan to make use of PWM so switching frequency is "DC".
How should I think when deciding on the resistor values? I chose this combination because it gave me a ~2.5V drop plus whatever drop is present through the darlington pair since I probably don't need more than -7V or so between gate and source since the currents in the LED lamps probably will not be more than a few hundred mA.
Yes that should work well, but add a 15V zener across the MOSFET gate/source to protect it from voltage spikes on the 12V supply (which in a vehicle can be very noisy indeed, easily enough to blow up a MOSFET gate).
BTW the very high on-resistance of the AUIRF6215 would not be suitable for tungsten bulbs. I don't know why you've gone for a 150V MOSFET here, 55V is the normal automotive rating and such parts will have much lower on-resistances. 30 milliohm is a reasonably good on-resistance to aim for in a low voltage p-FET, 10 milliohm for n-FET.
Yes I also noticed the fairly high on-resistance but the reason for this specific choice was the low QG which (as I understand it) is the charge needed to turn the mosfet ON. There were other ones that looked good but had much higher QG.
Perhaps IPB45P03P4L-11 with RDS on of 10.8 mΩ would be better suited. It has only slightly higher QG
