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LiPo battery charger query

Discussion in 'Power Electronics' started by hrishib, Jan 1, 2014.

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  1. hrishib

    hrishib

    34
    0
    Aug 30, 2013
    I'm trying to build a simple battery charger based on Microchip's MCP73831. I could build the schematic as it is which is very simple (as shown here).

    The STAT pin can be connected to an LED which shows the charge state (as shown in the table).

    With this schematic only the 'Charge in progress' status is shown by the device and when the charge is complete I'm guessing the LED goes off. How can I add another LED which shows that the charge is complete? I tried designing another circuit but I'm not sure if this works (shown here as well). Any ideas anyone?
     

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    Yes, what you've suggested should work.

    I've looked at the datasheet for the MCP73831 and the stat output is a push/pull output which will be able to both source and sink current.

    I'd probably make one red and the other green.
     
  3. hrishib

    hrishib

    34
    0
    Aug 30, 2013
    Thanks Steve!
     
  4. flotul

    flotul

    8
    0
    Sep 11, 2014
    [​IMG] Hi there,

    I'm doing the same circuit with two leds (either sinked or sourced by the STAT pin) like the ones on the attached picture.
    [​IMG]
    My problem is that I never have the leds OFF (STAT pin is Hi-Z) when I disconnect the battery from the charger chip.

    When the battery is disconnected, I still have a LOW level on the STAT pin.

    What am I doing wrong?
     

    Attached Files:

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    You could try something like this:

    MCP73831 (3).jpg

    This will have the LEDs turned off if the stat pin goes Hi-Z (rather than having them both on)

    However there is no indication in the datasheet that the output ever goes Hi-Z (at least not for the MCP78381). My reading is that it is low unless the battery is charged.

    This indicates one other possibility...

    MCP73831 (4).png

    In this case the power to the "charging" LED comes from the battery under charge itself. Once you remove that battery the LED cannot light.

    The disadvantage is that
    1. The device may produce an output voltage without a battery present.
    2. You may discharge the battery through the two LEDs and the resistors when 5V is removed from the circuit.
    3. (edit) You must make sure that the LED current is less than the minimum charge current.
    This is something you'd have to try. As long as the stat pin goes low when the battery is removed no LED will light.

    A suitable choice ov LEDs, or possibly series diodes with the LEDs may reduce the leakage current to a very small value.
     
  6. flotul

    flotul

    8
    0
    Sep 11, 2014
    Good ideas indeed, Steve!

    I'll have a try and come back for feedback.

    Thanks again for your quick reply ;-)
     
  7. flotul

    flotul

    8
    0
    Sep 11, 2014
    I was relying on the figure herunder found in the latest datasheet; if the STAT pin doesn't go to Hi-Z state, what should I have understood about Shutdown and No Battery Present?
    [​IMG]
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    OK, in that case my first solution should work.
     
  9. flotul

    flotul

    8
    0
    Sep 11, 2014
    I tested again; still the STAT led doesn't go off.

    Either I have something so wrong in my circuit I don't see it anymore or...I don't know.

    I'll change the chip tonight and try again...

    Fyi: my chip is a MCP73831T-2ACI/OT (SOT23), Rprog is 5.6k, Li-Po battery is KOKAM 3.7V (charging 4.2V) 700mAh model SLPB393459H TW, chip is powered from PC USB (5V), measured charge current at start is 181mA, after one hour 158mA, after two hours 110mA, after three hours 55mA, after four hours 18mA, after five hours 1mA.

    No answer from MICROCHIP support yet :-(
     
  10. flotul

    flotul

    8
    0
    Sep 11, 2014
    ....works fine now: chip was defect :-(

    Thanks for the help.
     
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