一个基于51单片机的PFM型开关电源代码，用EXB840来驱动IGBT，1602显示开关频率，可以直接通过键盘输入频率，步进为0.5KHz。-51 SCM-based PFM type switching power supply code, EXB840 used to drive the IGBT, 1602 show that the switching frequency can be directly through the keyboard input frequency step