说明：  模拟PID控制的开关电源系统存在电路复杂，调整困难，可靠性不高等问题。本文借助于DSP芯片强大的运算功 能，将模拟PID控制进行数字化改进
( simulation of PID control switch power supply system is complex, difficult adjustment, circuit reliability of problems. This paper by DSP chip powerful computing power Can, the simulation of digital PID control improvement)