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 overcurr