USB supply/charger - tips needed

Discussion in 'General Electronics Chat' started by kaning, Aug 5, 2014.

  1. kaning

    Thread Starter Member

    Jun 2, 2014
    Hi all,

    Im building a portable project where i use internal Li-Po battery as power supply. This internal battery is charged via mini usb/usb whatever.

    And here is where i need some guidance, how to plan the schematic of this particular part? when battery is charged, it feeds all circuit; when battery is empty and i plug USB it feeds circuit and charges battery.

    General purpose question is: what kind of circuit, IC should be used when you have some project fed by internal battery and you want to charge it via USB while On, so it charges battery and supply circuit??(as we see in pretty much portable device(mp3,phone,laptop etc? many thanks in advance
  2. timwhite


    Apr 10, 2014
    Well you would definitely need a voltage regulation circuit, as you would most likely be using a battery with a different supply voltage than the voltage of whatever device you're going to be charging. This can be done with a simple 5V regulator, like the LM7805. Aside from that, maybe some digital logic with buttons for charging battery and/versus supply. And don't forget a heatsink if you're working with a higher-voltage Li-Po battery, as not only do the batteries get hot, but so do the voltage regulators that you would use. Check the datasheet for their max specs.
  3. kaning

    Thread Starter Member

    Jun 2, 2014
    Thanks for the reply!

    yes i know about that. in this case LM7805 its not good option because it has huge v drop. i will feed circuit with 5v from usb port wich is already regulated, then its connected to IC MCP73831 to charge Li-Po battery. This IC regulates voltage to 4,2v and manages charge cycle of the battery.

    when battery is full it passes by a step up regulator to get exaclty 5v to feed audio amp. Im looking for solution that makes circuit work something like this when it senses USB connection