LTSPICE p chanel simulation not working

Thread Starter

acheriti

Joined Apr 26, 2020
26
Hey guys,
I'm getting started on LTPSICE and I'm trying to do a simple p chanel mosfet simulation.
For a reason I can't figure out it does not work the way I want it to.
You'll find the circuit in the attached pictures and the results of the two situations.
I have two scenarios :
1. N CHANNEL mosfet M2 is put on by the 5V source. The voltage of the gate of the P channel M1 is thus 12V, so the Vds voltage should be -12V. M1 should then conduct and the voltage at the output should be 24V.
2. N CHANNEL mosfet M2 is put off by the 5V source. The voltage of the gate of the P channel M1 is thus 24V, so the Vds voltage should be 0V. M1 should NOT conduct and the voltage at the output should be 24V.
I Can't figure out why but on the second scenario I still get 24V at the output.
Thanks a lot for the help guys !
 

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crutschow

Joined Mar 14, 2008
30,103
You have M1 with the source and drain reversed, so the current is going through the parasitic substrate diode.
A P-MOSFET must have the source more positive than the drain so reverse the source and drain in your schematic.
 

Jony130

Joined Feb 17, 2009
5,351
Body diode is the answer to your question. Flip the P-channel MOSFET so that the Source terminal is connected to Vin.
 
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