Abstract
An electrical control unit of constant voltage and constant current is designed on base of the current special chip NCP1200A.When In a constant voltage state, output voltage is adjusted and controlled by switch, jumped over the period to maintain. Adjust to and the cycle of proportion to maintain the steady output voltage, and can keep the efficiency of the whole load range was optimized. in the charging circuit by an adjustable temperature temperature compensation circuit. A constant flow of control unit began its task is to lessen the load resistance to the circumstances, the output of the current value as a constant stream remain unchanged. this needs to load output voltage with resistance in decreased and then, in extreme cases, the resistance resistance value is zero （ a short circuit state ）, output voltage also reduced to zero, to maintain the output of the constant current. This is a constant flow of parts, in a constant flow of parts, components are also in a constant pressure on, it is no longer in output voltage. in the end of the use of software design protel drawing circuit diagrams and pcb board hardware and complete fabrication and debug.
Key word：NCP1200A；constant voltage and constant current circuit；Temperature compensation circuit
