Hi Everyone,

First post in the forum after reading for quite a while in school, so I hope this is in the right place. I am working on a LiPo battery charger for a single cell 3.7V battery. I found a schematic online to build (attached below) but I had to make some changes because of the availability of parts at school. I made these changes:

BC857B were changed to BC560C
BCP68 changed to 2SC13830R
BSS138 changed to 2N7000

After building the circuit with these substitutions, I got an output voltage of 4.6 volts which is about 0.4V too high to be safe for a lithium battery. My question is, can I change the resistor values (which resistors?) to make the output voltage lower? I don't fully understand the principals of the transistors and they are the only parts I have available. I don't have computer modeling available to me at this time so I can't put it into any software at school yet. Thanks so much for any help!

 

Charging LiPo batteries require certain requirements to be followed.
Max.

 

That is a very interesting article, thank you. I do believe that the circuit in the original design was supposed to accomplish these goals without a micro controller and the charge current should decrease with as the battery charges. The LED indicator illuminates less as the battery becomes more charged.

Maybe I am wrong and this transistor design does not accomplish this? Thanks!

 

careful, even slight overvoltage/overcharge may cause the lipo cell to go on fire or even explode.

better to use lipo charger ICs for these.