说明：  实用的步进电机驱动电路 利用LM331、PMM8713 和SI － 7300A 设计了四相步进电 机驱动电路，该驱动电路具有工作可靠、效率高、矩频特性好 的特点，并应用于数控等离子弧压自动调高系统中
(Practical step motor drive circuit Using LM331, PMM8713, and SI- 7300A designed four-phase stepping motor Machine drive circuit, the drive circuit has a reliable, high efficiency, torque-frequency characteristics of good Characteristics, and applied to automatic CNC plasma arc to increase the system pressure)