I'm trying to use a mosfet as a switch in a low power application(<
100uA). The mosfet will turn off the device. With V_GS = 0V how well does the mosfet do this? The drain leakage in the data sheet says around 10uA. Does this mean that the mosfet will act like a 1M resistor for 10V Vcc? What I'm worried about is that my device my not turn off completely due to the leakage of the mosfet.Thanks
It would help if you included a part number, or spec sheet link. What's the on resistance? Since you've got small currents you can probably afford more on resistance which should help with the leakage.
George H.
"Juo"
** This popular one has a max 1uA leakage at 48 volts.Goes up by 1000 times at 125C but.
Stay cool.
.... Phil
A 2N7002 will have drain leakage in the nanoamps (or maybe picoamps) with zero volts on the gate. It's spec'd at 1 uA/48 volts at room temp. The specs are what's easy to test and are often pessimistic by 4 or 6 orders of magnitude.
The leakage isn't linear like a resistor either. It's closer to constant-current.
I have some 2N7002 data around here somewhere. I'll try to find it.
Measure a few of the fets you plan to use. If it's a million times below what you can stand, it's probably OK.
(So many people ask questions here, when they could actually measure stuff.)
John
I did think about measuring it but I do not have the equipment to do so accurately.
I wonder if there are on "off resistance" graphs floating around? Say with the gate tied to the source and V_DS vs I_D and V_DS/I_D plotted. If not, if you have the equipment would you mind doing so? If you get the data points I'll create a fancy graph for them. 2N7000 and maybe some power mosfet will work. Probably don't need to many data points. Maybe 5 in increments of 2 or 3V.
Some 2N7000 data:
Floating gate, leaves it on or off for hours:
ftp://jjlarkin.lmi.net/2N7000.jpg
The gate leakage must be electrons per second.
Drain leakage:
ftp://jjlarkin.lmi.net/2n7000_off_leakage.pdf
John
THANKS!!!! Did you do this yourself? If so, what kind of equipment to automate it so easily?
The data seems to suggest the mosfet has an off resistance much larger than 100kOhms. The resistance from 0V to 0.2V is about 0.1TOhms or around 1M times as large as the datasheet sugggests. What V_DS were these ran at?
I don't recall where I got that one. Win Hill maybe? I have done some spot measurements of 2N7000s and got pA leakages. I use my old analog Keithley electrometer.
John
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