How to prevent deep discharge of Li-Ion Batteries?

Discussion in 'Homework Help' started by vish2207, Jun 5, 2014.

  1. vish2207

    Thread Starter New Member

    Jan 28, 2014

    I have worked on the battery powered devices for the first time. So, this might be very basic problem for every one who have worked with portable devices.

    I have used 2 Li-Ion batteries in series to get 5V using LM7805. I have used MCP73213 for charging of 2 cell Li-Ion batteries. I am attaching the power diagram through which I am charging the Battery with programmed current of 200mA. I don't have any problem with charging.

    When I keep the battery connected all the time with device, it gets deep discharged despite putting my MCU in to sleep mode which draws about 100uA. The power that is being drawn mostly is by LM7805, which is about 3mA in idle condition. How can I prevent the deep discharge of the battery and keep connected battery to the device.


  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Under voltage cutoff circuit
  3. crutschow


    Mar 14, 2008
    You can also reduce the sleep current by using a low-power voltage regulator with a smaller bias current.
  4. vish2207

    Thread Starter New Member

    Jan 28, 2014
    Thanks for your reply.

    @R!f@@: Can you please suggest or point out reference circuit?

    crutschow: Can you please suggest alternatives for LM7805 with low sleep current?

  5. takao21203

    Distinguished Member

    Apr 28, 2012
    you can use a p=channel digital MOSFET.

    Since the voltage is very low, preferably a high power DPAK MOSFET.

    With a large resistor to VCC at the battery.

    Then you bridge that with a pushbutton to GND, and also hold it with the microcontroller.

    You measure the voltage every minute or so, and if it become too low, release the MOSFET gate.

    Normallly you shuold use a dc/dc converter to get stable 3.0 or 3.3 volts, and they often have an enable pin.