Tuesday, November 25, 2014

NiCd/Li-ion/NiMH Battery Charging Circuit With High and Low Power Indication, and Automatic Cut-off

First things first, I don't usually write articles like this and I am writing this article only to showcase a battery charging circuit me and my friends made for a college project.

The circuit is designed to charge 3 NiCd batteries of 1000 mAh each but can be modified to be set at any battery voltage and the circuit can be used for any battery type.


  • 230 V to 9 V Transformer (Or 110 V; depends on the AC Mains voltage where you live)
  • Bridge rectifier. We used one similar to 4 1N4007 diodes but you can use any that you find.
  • 470 microF, 50 V capacitor which is used as a filter.
  • LM7805 Voltage regulator.
  • LM741 op amp x3
  • BC547B NPN Transistor
  • 1 kiloOhm Resistor x5
  • 1.2 kiloOhm Resistor x2
  • 2.7 kiloOhm Resistor
  • 2 LEDs (1 red and 1 green)

The voltage at the node connecting R1, R2 and the U1 op amp is ~3.64 V which is the full voltage of the battery.

This circuit is designed in such a way that the current going into the battery getting charged decreases when the voltage increases and the current gets automatically cut-off at 3.64 V.

Most of the charging current going into the battery comes from the emitter of the NPN Transistor.

For high and low battery indication, 2 LM741 op amps are used as comparators. The D1 LED is green, indicating full charge and the D2 LED is red indicating low charge. 

In the circuit diagram, the +5 V voltage source is the equivalent of the circuit containing transformer, bridge rectifier, capacitor and LM7805 Voltage Regulator.

Link to .asc file to access circuit in LTSpice:  https://drive.google.com/file/d/0BwawuPAjHYZSdmNCM3lVclA1RkU/view?usp=sharing

I also want to tell you about two of my friends' blogs who are in the same college as me.
Maitrey Mehta: infotechpundit.blogspot.com
+Shreyas Patel : spatels.blogspot.com

That's it for this article guys! I may write some more articles similar to this displaying my college projects. Feel free to write any comments/suggestions/questions in the comments section below. Keep reading! :D


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