I need to build for a hobby project, a active balancing circuit for large number of LiIon series cells (90 cells). So it needs to be cheap but efficient :) (ie. not resistive dup). After lot of research, I found this circuit on internet
with the schematic as follows
Now the explanation of the author is quite poor, saying that the buck will "track" the VBAT/2 which is VCOM. I really don't fully understand the principle, so I can scale for my needs. Also, I'm puzzled about efficiency.
If buck's FB is feed by VBAT/2, then the buck will (try to) regulate VCOM (middle) to VBAT/2 which can happen only when (after) batteries will have the same voltage.
This can work only if bottom BATT has lower voltage, so BUCK, absorbing energy from both, will charge it until become equal.
But what if this bottom BATT has higher voltage? The BUCK will try to equalize the same, but as far as I see, will discharge it through buck SW itself (synchronous, lower side mosfet). So BUCK needs to be synchronous one for sure.
Am I missing something?
What does the 2'nd OPAMP denoted LPF filter?
Thank you in advance for further clarifications.