I want to replace a mechanical switch that supplies 5v at 300ma, to a display board. The board is permanently grounded, so I think a high side switch is the correct option. It will be switched using a processor output at 3.3v.
I can't find a suitable logic enhanced P-channel MOSFET that will handle around 1 amp, just much larger currents, so I'm thinking about using a BC516 Darlington PNP transistor.
At this point I'm not sure what to order and which way to go, so I'm stuck. Advice is appreciated. Thanks.
EDIT: Will an IRLML6401 work? I'd rather have a through hole part, but it has a gate rating of 1.8v and it will handle the current. If so, what are the appropriate resistor values to use? Thanks again.
For 300mA load you want a MOSFET rated at 5A or more anyway, just go with it. You should be
choosing MOSFETs based on the on-resistance, not the max current. Pick a device with on-resistance
of 0.2 ohms or less (it can be much less, not a problem). Make sure its logic level.
If you are anywhere near the max current, you've made a design error, as this means the device
will need lots of heatsinking and/or fan cooling. Max current is a usually thermal limit you want to keep
well away from (for continuous duty at least).
The IRLML6401 only has an abs max gate-source voltage of +/-8V, so I'd definitely avoid that, far
too delicate. Most devices will have +/-20V or higher ratings for the gate oxide, that's good.
A pullup woud work except that will apply 5V to your processor pin. Is that chip 5V tolerant? The only Arduino variants I know of that are is some but not all of the Teensy series.
A better way is to switch an N type MOSFET which then switches the 5V pullup for the high side.
Thanks for pointing that out. I should have seen it. I'll use either an ESP32 or MKR1000, both not 5v tolerant. I found the attached circuit online. I think it's what I need, except it is switching 12v and the diode won't be necessary. Will it work?
