A much more efficient method of controlling the voltage applied to
the motor is the pulse-width modulation method. In this method a
variable width pulse of voltage is applied to the motor. A diode is
placed in parallel with the inductive motor path to provide a circuit
for the inductive motor current when the switch is opened. This
circulating current path prevents abrupt current changes and resultant
high voltage across the switching device, while allowing more
average current to flow through the motor than is taken from the
battery.