Npn mosfet driving problem

[bggklp]

hi i'm doing a battery balance project while using your mcu. i have an technical question for using battery. i'm using npn mosfet and for controll the batteries which are series connected. can i send 5v
to npn fet for make it logic 1? or do i have to
send to higher voltage of batteries(higher than 70v)?

 

[ysba]

For each FET, you have to put a minimum voltage (threshold voltage, see datasheet) which is refererenced to its source. From the bottom FET it's ok because the source is connected to the GND, so it will turn on with 5V. But for the upper FET, say that there are 30V applied to its source. In this case you have to put 30V plus the threshold voltage (something like 35V referenced to GND).