实现85伏20安电流的控制，通过旋钮设置数值，实现恒压恒流，过压过流保护，通过外置AD,DA实现精确的数字控制和输出。(The control of 85 volts and 20 amperes is realized. By setting the value of the knob, we realize constant voltage and constant current, overvoltage and overcurrent protection, and achieve pr