12V Sealed Lead Acid Battery Dual Level Float Charger

When the 18V input voltage is added, the series power tube TIP42C is turned on and starts high-current constant-current charging. The charging current is 500mA. At this time, the charging current remains unchanged and the battery voltage gradually increases. When the battery voltage reaches 95% of the overcharge voltage Voc (i.e. 14.25V), the battery enters the overcharge state. At this time, the charging voltage is maintained at the overcharge voltage and the charging current begins to decrease. When the charging current drops to the overcharge termination current (IOCT), the 10th pin of UC3906 outputs a high level, the comparator LM339 outputs a low level, and the battery automatically enters the floating charge state. At the same time, the fully charged indicator light-emitting tube lights up, indicating that the battery is fully charged.