purpose of Schottky diode in the circuit

Question

Hello 
 i came across a circuit as shown below. here 20 volt battery is used as source. microcontroller is used to switch the NMOS. i am not able to understand the use of the diode placed across the gate and source of the PMOS. can anyone explain? 
 
 Thank you

shabaz · Accepted Answer

Hello, 
 (Replying from mobile so will be brief) 
 I think this circuit is a mess, better to look for a more appropriate one, it has quite a few flaws. Anyway it is more likely a Zener diode even though it says Schottky, and I'm guessing it was an attempt to protect the gate of the P-ch MOSFET since it may only be rated to say 20V or less, and the supply voltage could easily be higher. Also since you have it in a simulation package (looks like TINA simulator?) you could simulate this.

dougw · Answer

If the voltage divider is calculated to handle both high and low battery voltage extremes and circuit switching speed requirements, then the zener is just for insurance. 
 The battery won't have transients but it can be a bit higher than its nominal rated value.

purpose of Schottky diode in the circuit

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