Battery Charger Circuit

LM317_90pxThe circuit can be used to charge 12V lead acid batteries.


Pin 1 of the LM317 IC is the control pin which is used to control the charging voltage, Pin 2 is the output at which the charging voltage appears, Pin 3 is the input to which the regulated DC supply is given.

The charging voltage and current is controlled by the transistor (Q1), resistor (R1) and POT (R5). When the battery is first connected to the charging terminals, the current through R1 increases.This in turn increases the current and voltage from LM317. When the battery is fully charged the charger reduces the charging current and the battery will be charged in the trickle charging mode.



  • The input voltage to the circuit must be at least 3V higher than the expected output voltage. LM 317 dissipates around 3V during its operation. Here I used 18V DC as the input.
  • The charging voltage can be set by using the POT R5.
  • The LM 317 must be mounted on a heat sink.
  • All capacitors must be rated at least 25V.
  • You can use crocodile clips for connecting the battery to the charger.

Original Author: LM317 Circuits

Posted: 8 years 7 months ago by Jon Chandler #6193
Jon Chandler's Avatar
Very nice simple design. This should work well for charging SLA cells (sealed lead acid cells AKA Gel-Cells).
Posted: 8 years 7 months ago by Jon Chandler #6234
Jon Chandler's Avatar
Original Author]

It might be noted that this circuit appeared in National Semiconductor's Linear Brief 35: Adjustable 3-Terminal Regulator for Low-Cost Battery Charging Systems, dated August, 1976 and has been published on a number of different web sites.

It's still an effective and simple battery charging circuit.

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