ABSTRACT
From the circuit designer’s viewpoint, the fundamental difference between bipolar and unipolar motors relates to the fact that bipolar motors contain a single winding per phase. Bipolar motor circuits require changing current polarity during stepping operations and that this is usually accomplished with an H bridge of one type or another. Bipolar stepper motor performance is dependent on the drive circuit to a high degree. Higher speeds are achieved by reversing the stator poles more quickly, which also results in a gain in torque. However, increasing the reversal rate of the poles also increases inductance in the wiring. But, the higher inductance can be overcome by increasing voltage, but this requires limiting the current at these higher voltages. These considerations have led to two different types of bipolar stepper motor circuits: one in which the voltage is held constant and another one in which the current is held constant. The constant-voltage type is sometimes known as the L/R design.
