USB li-ion charger revision

An year ago, I’ve shared a circuit of USB li-ion charger based on LM358opamp. The circuit had some problems as reported by commentators that inclide wrong direction of LEDs.


  • Charging via mini-USB connector which is very common.
  • Charging status display by LED
  • Simple circuit by using opamp, resistor, and not by any complex dedicated IC or micro-controller.
  • Charges completely drained (0V) battery packs.
  • Max charging current 500mA(limited by USB supply), depending on battery.

Here’s the corrected schematics and the board design of the circuit.



Boards are available for buying.


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34 Responses

  1. MR says:

    Hi again, it’s not charging properly, my batteries charged all night and didn’t stopped… when i saw, it was like 4,6v and full charging led didn’t came up… any idea? when i have the li-ion battery disconnected, the tension is 4,12v. when i connect it, the value gets down to the same as the battery and starts to charging.. but didn’t stop charging.. i just changed the r4 value, as i described up… i think i’m really close…

  2. carlos says:

    hello I would like to buy your USB charger li-ion revision
    I’m in Brazil, you can send to me?
    thank you

  3. c-d says:

    Out of curiosity, why go with both the negative and positive inputs on the collector, And not pin 2 to the collector and pin 3 to the emitter?
    I am not bashing it because I’ve built it and it works well.

    Also would it be plausable to use the pnp to switch on a darlington or other current boosting transistor. (pnp collector to npn base) . Only because the tip 102 darlington is quite common at places like radioshack..

    I also added a mc34063 simple boost from 3.7 to 5.5v to a usb female jack to turn this into a sweet battery backup charger. As well as a 6v solar panel input for sunny days.

    Thanks for sharing

  1. July 4, 2013

    […] Navarro built a USB li-ion charger on breadboard. Now he is working to get it fine tuned to accurate voltage levels. He scored a free […]

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