Circuit for recharging 1s Li Ion Pack

Thread Starter


Joined Jan 18, 2021
Hello everyone

my hobbys and my curiosity led me to a point where I would like to tackle my first simple circuit and design a little PCB.

I have some very basic understanding of the fundamentals but especially when it is about components, ICs and what they are doing, I‘m still a Little confused. In fact I’m not asking for a working solution here but more for what I need to look into and maybe what I’m missing out.

I dissected a rechargeable LED Lamp that came with a 1s2p LiIon 18650 pack which is being charged over a standard USB wall plug. The 18650 cells don’t seem to have their own BMS and it looks to me like the little IC on the PCB seems to handle the over-/undervoltage Protection. It got pins for a charge status LED, a big Ground Pad on the bottom that probably just gets rid of the heat and some resistors and caps that I’m not entirely sure what they’re doing. However there’s no FET that is turning off the load on the battery so I‘m assuming that it’s handled within the mystery chip? The positive lead that comes from the usb charger is coming from the big solder joint undearneath the big R300 resistor.

I have looked everywhere for the name of the module and other MSOP-8 Li-Ion Protectors but I found nothing that works without a FET or in this type of package. Since I’m very inexperienced I‘m trying to replicate what I have on my hands and learn more about the topic as I go along.

The alternative would be of course to just buy a tiny BMS and hook up the batteries directly but my challenge is to combine the LED Driver and the Power Management in another package.

I would be happy if anyone can give me a hint in the right direction so I can move forward with my project and get this thing working :)




Joined Nov 6, 2012
You didn't specify the Charging Current desired, or the Supply Voltage.
Does it need to be all microscopic SMD construction ??
There are about 10-million unique chips designed for this job, or,
it can be done with a breadboard design and discreet parts.
What problem are you trying to solve ??


Joined Jun 5, 2013
Apple, Samsung, and Boeing had disasters with Lithium Ion chargers, and you want to do this as your first project? That’s sort of like making Nitro-glycerin in your first chem lab.

Make sure you keep up your payments for fire insurance.