U-131 Simple Switchmode Lead-Acid Battery Charger

Lead-acid batteries are finding considerable use as both primary and backup power sources. For complete battery utilization, the charger circuit must charge the battery to full capacity, while minimizing over-charging for extended battery life. Since battery capacity varies with temperature, the charger must vary the amount of charge with temperature to realize maximum capacity and life. Simple, low cost circuits are currently available for small, low power requirements, while more complex solutions are affordable only on larger more expensive systems. Often the greatest challenge is in designing mid-size, mid-price systems, where obtaining optimum performance at moderate cost and complexity may be nearly impossible without dedicated integrated circuits. This paper describes a compact lead-acid battery charger, which achieves high efficiency at low cost by utilizing switchmode power circuitry, and provides high charging accuracy by employing a dedicated control IC. The circuit described can be easily adapted to lower or higher power applications.