Imagine a small two-wire DC motor driven off a single battery, so 1V to 1.5V. Think of those little pocket fans that people take to sproting events & picnics.
Running by itself directly off the battery, it draws 7mA to 9mA @1.5V on a fresh alkaline cell.
Now, I want to control this motor with an AVR with (say) 3.3V Vcc.
Given the rather modest current draw, is a MOSFET to do the switching necessary? Or am I asking for noise trouble if the motor is driven directly from the AVR port pin? Will back-EMF be a problem?
If I want to drive the motor directly with PWM to approximate the nominal 1.5V, should I run the "raw" PWM into the motor? Or RC filter it to more nearly approximate a DC level? Or maybe just a storage cap?
I'm thinking that with the modest current requirements we can skip the MOSFET to save the part, and PWM of the motor power from 3.xV will actually be more efficient than driving continually with the battery voltage.
For efficiency, will faster PWM be better?