Hi Audioguru Thanks your suggestion. But since the overcharging part is not my responsiable, I have no need to worry about it. And The out put must be controled manually so I can't use IC. So, in order to let user to choice between constant current charging and constant voltage charging, I have to built one voltage regulator and one current regulator in the same charger. right? If I really built the voltage regulator, the output voltage will keep as my setting no matter the situation of the battery. And the current regulator is the same right ??? If not could you teach me how to find the rang of load for the constant current output and the constant voltage output. Additionally, back to our circuit. Do you mean that both your lab supply and regulator in market are trying to keep the set current first ? But by my limitted knowledge, I think your lab supply and the regulator can only limit the current not over a constant. Let say, if the load keep increasing and reach 80 ohm, (It just an asumption, is ture that in the actual world charging will only decrease the load of the battery ???) and the current drop to less than 1A(0.5A), then the circuit will still out put 10V and 0.5A. The circuit can not make sure that the output current is kept in 1A, if the load increase. Thanks very much