This battery charger circuit provides the Automatic cut off the facility when the battery gets fully charged.

Before the use of this circuit, you need to adjust the Cut off voltage range for the auto cut.

This adjustment is done by the 10k preset, and a multimeter connected with the output terminals that go to the battery.

This voltage range can be set by using any 4v to 15v DC supply which connects the terminals which go to the battery. And move the preset till the green led ON. Once the auto cut voltage is set, the circuit is ready to use.

Parts List for automatic Battery Charger

  • Transistor BC547 or use any NPN transistor
  • D1 Red LED, D2 Green LED, D3 IN5408 or according to Output current, D4 IN4007
  • Resistor R1 1k, R2 10k, R3 for 3.7-volt battery 220 ohms, 6volt-470 ohms, 12V 1k
  • VR1 10k
  • Relay for 3.7-volt battery 5V, 6volt- 5V or 6V, 12V -12V

Working of Auto Cut-off Battery Charger Circuit

  • In the above circuit, whole charging is governed by BC547 transistor and relay RL1 acts as the changeover.
  • During charging the circuits takes input via a charger /bridge rectifier charger circuit shown above and through the relay’s COM and NC, the power is directly connected to the battery.
  • After the battery reaches a certain level the transistor bc547 id tuned ON and it drives a relay which in turn changes the COM pin’s link from NC to NO which is connected to the red color LED that will start glowing after relay changeover, indicating the battery charging completion.

PCB Layout For Auto cut-off battery charger circuit

auto cut off battery charger circuit pcb layout

Automatic Battery Charger Circuit With LM317

This is a simple Auto cut-off Charger for Any Battery ( Less Than 7AH ) with well-known integrated circuit LM317. 

Charging takes place first in the current mode – Rising voltage, the current is constant. After reaching the target voltage (Vmax), the charger goes into voltage mode when the voltage is constant and the current asymptotically approaches zero.

LM317 Battery Charger Circuit Diagram

Charger schematic is shown below. Circuit LM317 serves as the voltage stabilizer. Li-Ion and Li-Pol Batteries are requires accurate voltage for charging. First Adjust the Output voltage as per your battery requirement. Check  Input and output voltage chart below for different batteries.

maximum charging voltage for all battries

Parts List

  1. LM317 1pc
  2. Diode D1,D2,D3 1N4007
  3. Capacitor C1 470uf/25v, C2 100nf
  4. Transistor Q1 BC547, Q2 BC557
  5. VR 5K or 10K
  6. LED 5MM 1pc
  7. Resistor R1 4.7 ohm, R2 1k, R3 1k, R4 220 ohm all 1/4watt
  8. Resistor R6 1 ohm for 2watt for 1amp, 2.2ohm 2watt for 500ma, 4.7ohm 2watt for 200ma

Circuit Working & Setting

The target voltage is set by trimmer VR . We set it without connecting the Battery, because the target voltage corresponds to the output voltage with no load. Stabilization of current is not as critical as the stabilizing voltage, so it is sufficient to stabilize it by a shunt resistor and NPN transistor. 

If the drop of shunt Rx reaches approximately 0.95 V (the total voltage drop of the NPN transistor’s B-E and diode 1N4007) transistor starts to open. This reduces the voltage on the pin adj and so it stabilizes the current. Current is depending on value of Rx. Select it according to the type of Battery. For charging current 500 mA, I used the value of 2R2. The value of Rx is calculated: Rx = 0.95 / Imax.

It is good to connect appropriately dimensioned fuse in series with the cell for safety reasons. Supply voltage should be in the range of about 9 – 24V. Too high voltage increases the power loss of circuit LM317, too low would not allow the proper operation (it is necessary to count the voltage drop on shunt and minimal voltage drop for the integrated circuit). LM317 circuit should be placed on a sufficiently large heat sink. The charger is resistant to short-circuit at the output. LM317 in worst case (short circuit) dissipates a power loss: P = U in x I max. ( Use Small Fan With This Circuit )

PCB Layout For Battery Charger Circuit with LM317

Just Download Below Image and Print it on a normal A4 Paper or you can download gerber file from link below

Watch Video For Details