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A practical simple battery automatic charger circuit

2015-03-20 08:43  
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A practical simple battery automatic charger circuit
The circuit principle of the charger is as shown in figure 4-18. The 220V AC city electricity is transformed, rectified and filted by this circuit to output the 20V direct current, and this current charges the battery through the three-port voltage stabilizer. The switching circuit TWH8778 can be used to detect the two-end voltage of the battery. When the charging starts, the voltage of battery is not enough to conduct the TWH8778, the equivalent circuit is as shown in figure 4-19(a). The constant current charges the battery, the constant current value I0=12.5/R, R is one resistance value of the R1-R4. When the battery voltage increases to the set value, the circuit of figure 4-19(b) is automatically converted into the circuit of 4-19(c).