Overvolt and reverse polarity protection

Owned by Daniel Puratich (Unlicensed)
2021-10-21
1 min read

For Zeropilot 2 overvolt protection is done with a Zener diode circuit and the reverse polarity protection is done with a P-Channel Mosfet. Additionally, it is worth noting for the power connector a screw terminal is used.

The Zener diode has a Vz of 6.8 volts which indicates that when the input voltage, ideally 5Vs, exceeds 6.8 Volts the current begins to short across the diode instead of destroying the circuit. The LDO for Zeropilot 2 can handle up to 10Vs in so that is why 6.8Volts is acceptable. The reason we don’t want to go higher is that the 5V rail is used to power a power on LED, PWM lines, and PPM lines so we don’t want to overvolt those.

For reverse polarity protection an enhancement mode P-Channel mosfet is used. As current in the proper direction is applied to the gate of the mosfet then it opens up fully allowing current to flow to the board. However, if the direction is reverse it will not be able to open the gate and therefore voltage will not go to the rest of the board.