Hi.
I am trying to create a highside power switch for a GPS so that I can power it up when needed. I also want to power its internal backup circuit, which means I cannot use a N-Channel Mosfet on the lowside/grd (as I need to connect GRD all the time). I want to switch the GPS on for several seconds to get a fix then off. Switching speed is not relevant.
Moteino Mega
NDP 6020P P-Channel Mosfet
Gate To pin 12 + 1K pull-up Resistor to 3.3V pin
Drain To GPS VIN
Source (Moteino 3.3V pin)
GRD GPS -> GRD Moteino
This is on a perfboard - hence the through hole. Moteino and GPS are on headers.
When no GPS is connected Mosfet works fine. 3.28V to GPS VIN when pin is LOW. 0V when Pin is HIGH.
When GPS is inserted into headers I lose Serial Output from the Moteino, and only see 1.2V from the Mosfet / on the GPS VIN pin.
If I connect the GPS direct to 3.3, GRD and Pins 12/13, GPS works fine.
Oddly. If I do a continuity check between drain and source, the GPS fires up, and serial works.
Thoughts? Its as if the mosfet cannot quite power up the GPS.
I want to use the same High Side Switch design with a GSM module. Hence want something that works. On the GSM I will be switching a LIPO on / off, so slight higher volts at 4.1 or 5V if charger is on.
I am copying this design (Felix's);
https://lowpowerlab.com/2015/01/30/weathershield-is-here/Nick Gammon has a similar example here;
https://www.gammon.com.au/forum/?id=12737&reply=1#reply1Ops. Just noticed both examples have a resistor in series with the Pin / Gate (gate resistor?). Can I use a 1K here? (or 560R, 100R as I have these in the parts bin).