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Wendy

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Wendy

Joined Mar 24, 2008
23,798
Is cutoff the important specification? In a past life I was a technician, not an engineer. I'd rather show my ignorance and cure it than not.
 
dl324

dl324

Joined Mar 30, 2015
18,330
Wendy said:
Is cutoff the important specification?
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It's one of the more important parameters.

If you wanted to operate with a 3V supply and reduce drain current to 100uA, you're going to need the gate source voltage to be close to cut off voltage for a typical 2N5457. If you got a worst case device, cut off would be 6V.

EDIT:
Cut off voltage is also called pinch off voltage. The voltage required to pinch off the channel.
 
dl324

dl324

Joined Mar 30, 2015
18,330
Wendy said:
Any other JFETs on Amazon that might work? I typed in jfet as the search keyword.
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Here's a parametric search for Digikey with Vgs(off) <= 2V and Idss of 5mA or greater.
https://www.digikey.com/en/products...FIAYgCiACpaIIiWgi7cALRgcBDa3LEcAJ5sYbpBqBISQA

You'll need to do a lot of searching because they seem to use unrealistic numbers for cut off voltage. I noticed that J112 came up and it has a pinch off voltage of 1-5V. Jameco has these for $0.29 (qty 10), but I considered the cut off voltage to be too high for your application.

EDIT: It appears that they use the minimum cut off voltage from the datasheet. That's pretty useless because cut off voltage isn't tightly controlled.
 
dl324

dl324

Joined Mar 30, 2015
18,330
J201 has a maximum drain current of 0.2-1mA. Do you consider that high enough for other potential applications? The Amazon listing states 50mA, but I trust the datasheet more.

J112 has a cut off voltage of -1 to -5V. You have no guarantees that you're not going to get some that need 5V to turn off. Or any that turn off with less than 3.5V.
 

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Wendy

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Wendy

Joined Mar 24, 2008
23,798
I'm going to out this part on the back burner for now I need something with through hole leads and easy (ie inexpensive) shipping and no minimum orders.

When I get the breakout boards possibly as late as June/July I'll revisit this component hunt.
 
MrSalts

MrSalts

Joined Apr 2, 2020
2,767
Wendy said:
At this point volts is not important, I am aiming for 100µa at 3V. This will become part of Project Parts Reference V2.0.
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if your Room temperature will be fairly constant, the E-101 current regulating diode from S is a super easy constant current source. It will hold 100uA at any voltage from 1 to 100v input.
If you can accept 300uA as your constant (since you are just looking for parts references) use the E-301. The temp stability is excellent - and it has good compliance from 2 to 100

they are about $2 each at Mouser but super easy. Available in SMD (s-prefix) and TH (e-prefix)


http://www.semitec.co.jp/uploads/english/sites/2/2017/03/P22-23-CRD.pdf
 
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