BQ24105 Switch Mode Lead Acid Battery Charger

Switch mode circuits can implement the lead acid battery charger with a more efficient. It can be constructed using bq24105 battery charger controller. The bq24105 was originally designed to charge single-, two- or three-cell Li-polymer and Li-ion  battery packs. The bq24105 doesn’t has a feature  to control lead acid battery charger termination. So external circuitry is added  to enable this controller to charge lead acid batteries. Switching mode charging method for lead acid batteries provides high efficiency, although the circuit becomes more complex. Here is the circuit :


Lead-acid battery charging system design specification:

  • Input power source Vin: 17 ± 1 Vdc
  • Battery bulk voltage regulation: 14.8 V
  • Battery voltage Vbat: 12-V lead-acid battery
  • Battery refresh voltage: 13.6 V
  • Fast-charge current: 0.5 A for Vbat ? 13.5 V, 1 A for Vbat > 13.5 V
  • Precharge current: 0.45 A
  • Termination current: 0.9 A

[Schematic diagram source: Texas Instrument Application Report]