Tom,
You would not want to put the motor coil in the emitter leg. The basic reason is that it becomes more complicated to turn the transistor on. Since the transistor requires about 0.7 V above the emitter voltage, if you put the coil in the emitter, you require 0.7 Volts above the voltage at the top of the coil.
This is not a problem at steady state conditions, since the voltage at the top of the coil will have decayed, but, if you are switching quickly, you will have residual voltage at the top of the coil. Then you need a much higher base voltage to turn the transistor on.
Much better to keep the coil in the collector.
Steve |