Zener Voltage = 10 V, Q1-VGS max = +/- 20V
Zener diode, D3 will protect the gate from excessive voltages/ unwanted spikes
By
referring the Gate signal to the ground line, the device is fully turned on when the
battery is applied in the right polarity. For the first start-up, the intrinsic body diode
of the MOSFET will conduct, until the channel is switched on in parallel. The Zener
diode will clamp the Gate of the MOSFET to its Zener voltage and protect it
against overvoltage.
By reverse polarity, the MOSFET will be switched off, because the Gate Source
voltage for this case will be positive (voltage drop over the Zener diode).
