Mosfet with 3.3v logic

Community Projects
1

I am banging my head for few days now and I cant seem to find a solution to this problem.

I made a bespoke pcb for Raspberry PI and I had these 3 mosfet p channel which worked fine with an expander IO that was outputing 5V at the gate but now that I can use the extra GPIO from the PI, I cant use these mosfet anymore due to the 3.3V max voltage on the pin.

I tried to use a level shifter to convert my 3.3V signal to 5V but unfortuantely on the gate I always had a drop of voltage, not sure why but it didnt keep a 5V constant.

One solution I found on the internet is to use a pull up between GATE and SOURCE, of 47 ohm and then use the 3.3V pin to drive the pull up, but this is pretty dangerous as it returns back a 5V into the GPIO.

I am not able to find a proper mosfet p channel so I heard I can use a logic mosfet but it needs to be able to switch a 5V @ 1A and needs to be a smd package. Can someone help me to find it out?

Current Mosfet: https://uk.farnell.com/vishay/si2301cds … dp/2335284

I attach my schematic at the moment

Screenshot from 2019-07-21 10-43-04.png
Screenshot from 2019-07-21 10-43-04.png696×352 3.27 KB

2

I would use a low-side n-channel mosfet with a pullup to 5V to drive the gate of the p-channel. When the n-channel is off, the pullup will turn off the p-channel (Vgs would be 0). When the n-channel is on, the gate of the p-channel would be pulled to ground, giving a Vgs of -5v or so. Just make sure that the p-channel fet has a suitable Rds(on) when Vgs is 5V; many don’t really turn on hard until Vgs is 10v.

/mike

3

So I found out a correct one which is this https://uk.farnell.com/nexperia/pmv50ep … st=2900300