Help with battery charging schematic

[looxuser]

Hello everyone, was hoping you guys could help me understand whats going on with this battery schematic for a toy lion battery. What I know is that component at F1 is a fuse that has heaters in it that are heated to deliberately fry the fuse and shut down the battery permanently in the event of overcurrent, cell imbalance etc. (Problem is its overly sensitive) It appears that a mosfet Q8 performs that function by grounding the BAT+ input at fuse terminal 1. the mosfet being switched by the IC21 that is monitoring individual cell voltages for imbalances. IC 21 was a special for Sony. Q1 is also a mosfet i believe which is there to close the BAT + to the toy when its sees and enable signal from the toy (that enable depending on SMBUS comms to the toy and satisfactory parameters). What I'm most unclear about is the function of Q7 its base routes to a TI bq2040 battery gas gauge (I wonder if it performs some switching function between charging and discharging. I can reveal more of the schematic later but what i can't get my head round is the flow of current in this circuit if anyone could help me out please? I also want to know whether desoldering the link at BL2 would prevent operation whilst i experiment with recelling.

If anyone's willing to talk me through additionally each component and what functions they perform I'd learn so much I've not been able to figure out, I would be massively grateful. Also it would be good to know what the Test points would be there for?

 

[Harald Kapp]

I know is that component at F1 is a fuse that has heaters in it

It is a dedicated LiIon protection component, see the datasheet.

IC 21 was a special for Sony.

Seems so. I can't find a datasheet. Explaining the function without a datasheet is not possible. Take it as a dedicated battery charger and/or balancer IC.

Also it would be good to know what the Test points would be there for?

For testing, what else? After assembling the pcb, the manufacturer needs to verify correct operation. Simply applying power to a pcb will how wether the pcb works or not. It will not, however, tell you (or the manufacturer) if there's an issue that may lead to premature fail of the pcb. Nor will it allow you to tell where's the fault in case the pcb does not work. Test points are used to enable access to internal nodes of the circuit for verifying e.g. correct assembly of parts, correct soldering, or to check internal voltages for correctness. Test points can also be used to inject signals into a circuit to force a bahavior other than the normal function. For example for trimming or programming components (the latter most likely here not being the case).

 

[looxuser]

Thanks Harald, yes indeed that's the protection component. Yes IC21 we can see could activate that mosfet thats shown on the fuse component you identfied. Regards the test points I should have been more specific i.e. what could you test for at each point, voltages, signals etc?. I wanted to build a table of all test points in the battery pack and how they could be used to troubleshot the circuit.

 

[Martaine2005]

Without a vey detailed schematic, or very in depth reverse engineering of a good working unit, your guess is as good as anybody’s.
Test points are just that, for testing.
Larger electronics manufacturers have testing stations that have probes mounted which contact various test points for each section of the circuit. This is automated and the PCB is rejected if it fails the particular test. Then a human will be involved to either change a component or add a bodge wire!,

Martin

 

[looxuser]

Thanks Martin, anyone offer an opinion of why Q7 is there, because this fuse unit would blow if the mosfet Q8 base was HIGH wouldn't it anyway? I think Q7 is a PNP so would current again not flow Emittor to Collector if Base was HIGH. I was also originally thinking the gate of Q1 was HIGH made by the toy but of course its always HIGH unless the fuse blows.