7.4V Li Ion battery charging from USB

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Cukrai

Joined Nov 9, 2013
13
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 :)
 

ScottWang

Joined Aug 23, 2012
7,397
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.
 
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Thread Starter

Cukrai

Joined Nov 9, 2013
13
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?
 

Papabravo

Joined Feb 24, 2006
21,094
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?
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?
 

ScottWang

Joined Aug 23, 2012
7,397
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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