Charger Circuit for Lead Acid Batteries by MAX773

The circuit utilizes the MAX773 current-mode controller and the MAX471 current-sense amplifier for charging lead acid batteries.

A current-limited power supply for charging is being implemented by a flyback converter. The output current is limited by the MAX773 and the isolation and flexibility are provided by the flyback transformer for input voltages both above and below the battery voltage. The charging current is being monitored by the MAX471 and feeds back to a threshold detector in order for the flyback converter to switch to a lower charging voltage below threshold for trickle-charge mode.

One conventional way of charging the lead acid batteries is maintaining a constant voltage across the battery by a current-limited power supply, until the charging current decreases below a current threshold defined by the capacity if the battery, which places the charge in a trickle-charge mode.

A trade-off between cell life and charging time are involved in the charging voltage. The time required can be minimized by high voltage although at full charge, the battery’s life is shortened by oxidizing its grid since it produces a large overcharging current. This current can be lowered by decreasing the charging voltage.

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