Question about a 12V Power PMOS Switches

[MrSun]

Hi everyone,there is diode(named 'D1') in the circuit of MiniPC.PrjPcb Project (one example from AltiumDesigner),but the Q20(Si7635DP-T1-GE3) has drain-source body diode,my question is:what's the function of the D1?

[qdrives]

D1 is a drawn as a Schottky diode. It has a lower forward voltage and lower (or no) reverse recovery time.

[MrSun]

qdrives thanks for your reply,i think it's DC supply only,because it supply to PCIE power direct.

[qdrives]

I made a mistake in my previous post. It is not a reverse protection (diodes should be the other way round). It is a delayed start.
On start-up C73 is 0V. C73 will be slowly charged through R131. When the voltage drops at the gate of Q20 enough it will switch on.
SW1 in this position keep the gate near supply voltage to the FET is off.
The requirement for D1 is still not clear to me.

[robertferanec]

it can be designed also for transistors with no diode in it or it may have something with the rest of the circuit or system e.g. reverse polarity protection (?) etc .... I didn't help much

[MrSun]

than you,i think only the designer can explain.