Published:2011/7/18 21:51:00 Author:TaoXi | Keyword: Constant current, constant voltage, dual-function, charger | From:SeekIC
The ordinary charger has the single function of the constant current charging or constant voltage charging. The circuit is as shown in figure 5-17. When the charging begins, the voltage of the battery istoo low to conduct the VS, the LM317 is connected into the form of constant current charging, the charging current I=1.25/R. When the voltage of battery invreases to the certain value, VS conducts, the pin-1 of LM317 is connected with the ground through the RP1 and VS, at this time, the charging mode is the constant voltage charging, the charging voltage U=1.25(1+R2/R1-0.7), R2 is the resistance value of RP1, R1 is the resistance value of R1. If the charge current is very large, you can connect a diode on VD2 in parallel connection state. The power handling of R is W》/=1.6/R. VS need to use the unidirectional thyristor with the small conduction resistance.
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