输入交变电源的电压220V，50Hz；直流电压的输出小于10V。

①　电流输入的大小范围：200mA到2000mA之间；

②　可以在允许的范围内通过矩阵键盘设定电流的预设值，显示模块会显示预设的电流值，设计要求预设电流与实际输出电流值相差的绝对值要小于或者等于输入的电流值的1％。

③　为了增强可调节性，该设计还具有加减的步进功能，步进为10mA；

④　负载的电阻改变，电压输出值同样不会高于10V，精度方面输出电流的误差绝对值要小于等于预设电流值的1％。

-The design of the subject adopts to improve simple current source and make it as current source circuit.Voltage controlled constant current circuit composed of a field effect transistor and operational amplifier OP07, the degree of saturation control effect tube to realize voltage controlled constant current. Using precision sampling resistance to obtain the feedback current signal, the load applied differential amplifier as the feedback voltage.The whole process using PCF8591 to convert analog and analog to digital.