In this article we study a Simple li-ion battery charger circuit Diagram with auto-cut off, current control features.

Simple Li-ion Battery Charger Circuit Diagram Working

Once the circuit is assembled and set up, the below shown design can be used for charging any spare Li-Ion Battery through the 5V Mobile Charger or USB port.

First connect the battery across the indicated points, and then plug in the USB connector with your Mobile Charger or computer’s USB socket. The green LED should instant become ON indicating the battery is being charged.

You can attach a voltmeter across the battery to monitor its charging, and check whether the circuit cuts off the supply correctly or not at the specified limit.

Simple Li-ion Battery Charger circuit diagram
Click Here To Buy

In this project, I will show you how to design a simple Battery Level Indicator Circuit using easily available components. Battery level indicator indicates the status of the battery just by glowing LED’s. This article explains you how design battery Continue Reading…

Parts List:-

  1. Transistor Q1 BC547, Q2 BD140
  2. LED D1-D2 Red & Green
  3. Resistor R1-R5 1k 1/4watt 5pc , R6 220 ohm 1/4watt
  4. IC LM 358
  5. Zener Diode D4 3V 1/4watt
  6. Capacitor 1uf/10v or 16v
  7. Diode D3 IN5408
  8. Connector 2pc
  9. PCB 

Click Here To:- Buy This Kit

How to Set up the above Li-ion Battery Charger Circuit

  1. First, make sure the preset is moved at the ground side fully. Meaning, the pin#2 should be at ground level through the preset initially.
  2. Next, without any battery connected, apply an Variable Power supply across the +/- supply lines of the circuit, 
  3. You will see the Green Led coming on instantly
  4. Now check the voltage at output and set output voltage at 4.2V With Variable Power Supply
  5. Now, slowly rotate the preset, until the green LED just shuts OFF, and the RED LED switches ON.
  6. That’s all! The circuit is now all set to cut off at 4.2 V when the actual Li-Ion cell reaches this level.
  7. For the final testing, connect a discharged battery to the shown position, plug-in the input power through Mobile Charger , and have fun watching the cell getting charged and cut-off at the stipulated 4.2 V threshold.

PCB Layout:

Li-Ion Battery Charger Auto Cut-off

How To make 3.7V LI-lon Battery Charger Circuit Watch The Video

Li-ion Battery Charger Circuit With LM317

This is a simple charger for Lithium-ion (Li-Ion) and lithium polymer (Li-Pol) cells 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 (Umax), the charger goes into voltage mode when the voltage is constant and the current asymptotically approaches zero.

At the moment the current is small, the cell is charged. Target voltage of Li-ion and Li-Pol accumulator is usually 4.2 V (for some types 4.1 V) Target voltage is not the same as the nominal voltage. It is generally 3.7 V (sometimes 3.6). The cell does not need to be charged the full 4.2 V, because it decreases its lifetime.

If you reduce the target voltage to 4.1 V, capacity drops by 10% but lifetime (number of cycles) will increase almost twice. When using the cells, they should never discharge below 3.4 to 3.3 V. Cells Li-ion and Li-pol do not like storing in a charged or discharged state, they should be stored partially charged.

Circuit Diagram of Li-ion Battery Charger Circuit Diagram

Charger schematic is shown below. Circuit LM317 serves as the voltage stabilizer. Li-Ion and Li-Pol is quite demanding on the accuracy of charging voltage. If you want to charge to full voltage (usually 4.2 V), it is necessary to adjust this voltage to with +/- 1% accuracy. Cells are very sensitive to overcharging. If you charge at 90% capacity (4.1 V), is sufficient a little less accuracy (around 3%). LM317 circuit provides a relatively accurate voltage stabilization. 

3.7V-Lion-Battery-Charger-Circuit-With-LM317

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 cell, 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 charged cell. 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. 

PCB Layout For Li-ion Battery Charger Circuit

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

Li-Ion Battery Charger Auto Cut-off

Watch Video For Making Process of Lithium Battery Charger