Sealed Lead Acid Battery Charger

The UC2906 series of battery charger controllers contains all of the necessary circuitry to optimally control the charge and hold cycle for sealed lead-acid batteries. These integrated circuits monitor and control both the output voltage and current of the charger through three separate charge states; a high current bulk-charge state, a controlled over-charge, and a precision float-charge, or standby, state.

Optimum charging conditions are maintained over an extended temperature range with an internal reference that tracks the nominal temperature characteristics of the lead-acid cell. A typical standby supply current requirement of only 1.6mA allows these ICs to predictably monitor ambient temperatures.

Separate voltage loop and current limit amplifiers regulate the output voltage and current levels in the charger by controlling the onboard driver. The driver will supply up to 25mA of base drive to an external pass device. Voltage and current sense comparators are used to sense the battery condition and respond with logic inputs to the charge state logic. A charge enable comparator with a trickle bias output can be used to implement a low current turn-on mode of the charger, preventing high current charging during abnormal conditions such as a shorted battery cell.

Other features include a supply under-voltage sense circuit with a logic output to indicate when input power is present. In addition the over-charge state of the charger can be externally monitored and terminated using the over-charge indicate output and over-charge terminate input.

When the load current decreases to 150 mA it enters flotation limiting the voltage 13.5 V. The red LED indicates it is in the first stage (initial). Yellow LED indicates that entered the second stage (voltage reached 13V). The green LED indicates that went into floating (charged battery). The cable that is connected to the battery should be short and thick so that its resistance does not interfere in the values ​​of shear stress. Circuit should be energized after the battery is connected. Should be used a heatsink in TIP32. Transformer should be 15V.


  • Optimum Control for Maximum Battery Capacity and Life
  • Internal State Logic Provides Three Charge States
  • Precision Reference Tracks Battery Requirements Over Temperature
  • Controls Both Voltage and Current at Charger Output
  • System Interface Functions
  • Typical Standby Supply Current of only 1.6mA