I'm designing a simple cell balancing for charging LiPoFe4 cells in series. In order to prevent overcharging, when on of the cells reach the maximum charing voltage, the microcontroller will enable the mosfet, to bypass the current to the next cell.
Consider the following circuit, where the 3.2V sources represent two cells, only with the top cell presenting the balancing circuit.
For the mosfet I intend to use, the max threshold gate voltage is 2.5V. Assuming the worst case scenario, the botom cell being fully charger, I'll have a Vs of 3.2V. With the bypass enabled, I'll have Vg of 5V from the microcontroller. Thus, I won't achieve the Vgs = 2.5V, and the mosfet won't transit onto its 'on' state.
The question, what would be the best way of workaroud here, not changing the mosfet? I thought, maybe, add a greater voltage reference and control this one with the microcontroller,but I still think there's something simple I'm missing.
Thanks in advance!