7.4V Li Ion battery charging from USB

Discussion in 'Electronics Resources' started by Cukrai, Oct 22, 2014.

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  1. Cukrai

    Thread Starter New Member

    Nov 9, 2013
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    Hello everyone!
    In my project I want to use a battery like this http://uk.farnell.com/bak/18650ca-2s-3j/battery-lithium-ion-7-4v-2250mah/dp/2401854 2 cells Li Ion battery pack. And i want it to be charged from USB port. Is it even possible to do that? Because USB output is 5V, and when charging a battery like this, do I need a charger circuit that can supply 4.2V and it charges each cell independently? Or both cells of this battery has to be charged at the same time, so it means that I need an input to the charging circuit bigger than the batteries voltage and I cant charge it from USB port?

    Thank you! hope you understood my question :)
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    You need a mc34063 dc to dc converter to converting 5V to 8.4V, or using mc34063 dc to dc converter to converting 5V to 12V and using Lm2576HV-adj to adjust to 8.4V.
     
    Last edited: Oct 22, 2014
  3. Cukrai

    Thread Starter New Member

    Nov 9, 2013
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    This is something what I was looking for! But don't I need an IC to charge a Lithium Ion battery? that controls charging voltage, current and prevent it from overcharging?
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,136
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    Yes, you do need an IC to charge a battery. If the charging source has a lower potential than the batteries you may need more than one. The suggested DC-DC converter is designed to produce a charging voltage that is higher than the battery voltage. What exactly were you expecting?
     
  5. Cukrai

    Thread Starter New Member

    Nov 9, 2013
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  6. ScottWang

    Moderator

    Aug 23, 2012
    4,853
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    If you want to choose MCP73864 to replace Lm2576HV-adj, that's ok, but you still need to use mc34063 and then connecting to MCP73864.
     
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