HI everybody,
i did some quoogling trying to find a P-Channel MOS-FET than can be used in 3.3V circuits. This means the MOS-FET has to "fully open" with a gate-source-voltage of less than -3.3V.
Seems to be hard to buy. I found one through-hole-type at mousers
IXTP26P10T delivering time 53 weeks!
If I reduce my requirements to gate-source-threshold voltage -8V to -12V can somebody recommend an easy to buy through-hole-type ?
best regards Stefan
I use whatever voltage suits the mosfet that i have, and drive the mosfet with an opto coupler which is driven by 3.3v or 5v, whichever is available. If you want to know which mosfet to use, most important is that you tell us what you want to control with it. The specs i mean, how much current and what voltage.
Yes of course better advice with better details or some details at all:
Well first detail: general purpose MOS-FET defined as
current minimum 5A Rds_ON resistance less than 0,2 Ohm
actual project: 12V lead-acid-battery over-dis-charge-protection with lowest possible power-consumption in case of battery-shut-off and still low current in battery switch on mode.
Most of my projects need a current of less than 1A. Sometimes 3 to 5 ampere
Usage switching on / off devices with lower frequencies than 10 Hz.
Sometimes typical PWM 5 to 20 kHz.
Having a MOS-FET type that can be used in a pure 3.3V-project means just grab one out of the box instead of ordering new.
As N-channel MOS-FET I'm using the IRF3708
Rds_on: 0,03 Ohm
up to 62A
gate-source threshold-voltage 2V
best regards Stefan
Hi,
Can you post your circuit diagram showing how you have the P-CH MOSFETs configured.
The gate has to be -3.3V with respect to the source.
Thanks.. Tom... 
Here is a schematic.
The capacitor is for some kind of a watchdog-circuit.
The IO-pin must be switched HIGH after some time to keep the MOS-FETs in on-state
but is switched to LOW after charging the capacitor.
With this I want to ensure that in case of a program-hang (except for hanging in IO-pin switched HIGH)
To "projects" having some P-channel MOS-FETs at all and the BODPS
B)attery-O)over-D)ischarge-P)rotection-S)system
best regards Stefan
Schematic didn't take..
Looks like it does the P-MOS VGS transition between 0V and -12V.
Don't you need a small N-MOS available at gate voltage to 3.3V, not a P-MOS?
Why did you think that only -3.3V could be given to the P-MOS gate?
In the BODPS-application of course there is a voltage-difference of 12V.
There will be a lot of MOS-FETs matching a gate-threshold-voltage of 12V.
The second is to have some kind of a general purpose P-CH-MOS-FET that is able to work in pure 3.3V circuits.
I found this example
which uses a quite small SOP23-MOS-FET which works down to even smaller voltages as a load-switch. Toshiba SSM3J338R.
After reading the answers here I decided to use a different approach for the BODPS
and take time later for the GPMF
Thank you all very much for answering and your ideas and questions.
best regards Stefan
Why the complicated circuit in post#7.
The LM2596 has an on/off pin.
Leo..
the IXP26P10T is not guaranteed to be fully OFF (or ON) at 3.3V
Keep in mind the Vgs specification is for conducting 250µA
What is your goal? Have you looked through Digikey's part selector?
interesting to know.
Do you know a ready to use DC-DC-step-down-board with the enable-pin accessible through a solderpad on the board?
hacking workaround:
and cutting-off Pin 5 and soldering a wire to the pin would enable using the enable-function
Maybe it has been "left open". Get out the ohmmeter and see if it's connected to GND.
If it isn't open circuit:
You might be able to cut a trace (with an X-acto or sim.).
Alternatively, heat the pin with a soldering iron, and bend it upward, gently say, with a tweezer (or somesuch) till it's not in contact with the pad/board.
I would use the cutter if it's THT and Heat with tin and lift with screwdriver as a lever on pin 4 if it is SMT
This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.
