I am proposing to control a simple D.C. very low current (circa 50mA) motor with an H-Bridge controlled by four outputs from a 14M2 chip - no PWM, just on/off and direction. I want the whole thing rather compact and therefore I don't want to use half of an L293D, but just a simple H-Bridge with four SOT23 MOSFETS. Now I have seen H-bridge circuits that use four N-channel MOSFETs and others that use two N-channel and two P-channel MOSFETs instead; the P-channel devices switching the high-side of the motor. I am now confused; I can only presume that four N-channel devices work so why do some designs use P-channel as well? The same seems to apply with simple NPN and PNP transistors; some designs just use NPN alone. Can the more knowledgeable help me with some advice/explanations as to the relative merits of these two approaches?