In the case of stepper motors, it is possible to enhance the energy delivery to the motors so that a battery of a lower voltage can be used. The basic principle is the same as a boost switching regulator. However, because a motor does not require an exact voltage, much of the feedback and control of a boost regulator can be omitted.
Furthermore, the boost circuit can deliver more power when a step just occur, then taper off as time progresses to save energy. See the following schematic for this circuit.
This circuit uses L1 to store energy when T1 is turned on. When T1 is abruptly shut off, the positive node of C1 experiences as much potential as necessary to keep the current going as the magnetic field of L1 collapses. The output of this circuit connects to a coil of a stepper motor. Because the instantaneous current to a coil (another inductor) is zero, we need C1 to buffer the energy released by L1.
Note that this circuit assumes all electrical charge of the capacitor will be discharged through the stepper motor coil before T1 is enabled. If this cannot be assumed, then a diode should be placed between the drain of T1 and the anode of C1, with the anode of the diode connected to the drain of T1.
By modulating the duty cycle as well as frequency of switching T1, the power delivered to the stepper motor can be software controlled. Note that an H-bridge is still needed for a bipolar driven stepper motor.
