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UC3906 battery charger circuit

This charger circuit diagram is based on the UC3906 battery charger controller that contains all of the necessary circuitry to control the charge and hold cycle for sealed lead-acid batteries. The UC3906 battery charger circuit is specifically designed to provide the proper charging voltage and current determined by the temperature and state of charge of the battery.
The UC3906 battery charger circuit controller monitor and control both the output voltage and current of the charger through three separate charge states .
UC3906  has separate voltage loop and current limit amplifiers which regulate the output voltage and current levels in the charger by controlling the onboard driver.The charger circuit requires 18 to 22 volts DC input.  Three optical ( LED ) indicators show the charge state .  The UC3906 IC is configured to provide three charge states:
Bulk charge – the charger operates in a constant-current charge mode until the battery reaches the programmed full-charge voltage.

Overcharge – when the voltage reaches the programmed full-charge voltage, the charger switches to overcharge mode to ‘top-off’ the battery.
Float charge – when the current decreases to the minimum overcharge current, the charger enters the float charge mode.
Voltage and current sense comparators are used to sense the battery condition and respond with logic inputs to the charge state logic.
How works these three states modes ?

If the battery voltage is between 10.2 and 12.2 volts  ( when charger is connected to the battery )  charging begins at the programmed bulk charge current and continues until the voltage rises to 14.0 volts. In this state mode only the power LED is illuminated .
When the voltage exceeds 14.0 volts, the overcharge LED illuminates (charger has entered in the overcharge mode) and charging continues  . The charge current remains at the programmed bulk charge rate until the battery voltage reaches 14.7 volts.
When the battery voltage reaches 14.7 volts, the charging current begins to taper off.
When it decreases to 1/10  of the bulk charge current, the overcharge LED extinguishes and the float LED illuminates to indicate that the charger has entered the float charge mode (voltage is maintained at 13.9 volts ).  The TIP transistor must be mounted on a heatsink , to prevent the damage of it cause of high temperature .

UC3906 battery charger circuit diagram

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