2N7000's Vgs

Hello Boki,

Level shit? That was a good one :-)

You can't buy that in a discrete FET. There are some that are called "logic-level FET" but look at the fine print. Often they are just scraping by at 5V, some at 3.3V. But 2.4V is too low for my taste, I'd certainly go with bipolar transistors there or with level shift.

Also, don't rely solely on the Vgs/Rds graphs in the data sheet for a design. Those represent "typical" values. There needs to be hard data, like maximum Rdson at your desired gate voltage.

Regards, Joerg

I read 2.1V typical and 3V max.

What part number?

linnix =E5=AF=AB=E9=81=93=EF=BC=9A

2N7000=20

Thanks. Boki.

Joerg =E5=AF=AB=E9=81=93=EF=BC=9A

sorry, typo ; )

I got it, thank you very much.

Best regards, Boki.

?? I don't think you will find discrete MOS with 0.7V Vgs(th).

I think there is discreet CMOS logic which will work OK down at that level.

And there are discrete FET's out there which will reliably (guaranteed by datasheet) turn on at 2.4V. You can sniff around at zetex, for example.

These parts are much more expensive than a 2n7002.

Good luck, Boki. I have a feeling you will need it. ;-)

--Mac

The BSS138 has a max Vgs(th) of 1.5 V at Ids=1mA, which is a higher current than many other threshold voltages are specified at.

With low-threshold discretes, you may find that the gate capacitance will be problematic, depending on what you are trying to do.

--Mac

nt

2N7000 has typical 2.1V Vgs. So if you buy a batch of them, most will turn on at 2.1V. However, even if you can turn it on with 2.4V, you can hardly drive anything. Unless you have another power source (step-up from 2.4V) for the drain, there won't be enough power for the load. Can you tell us more about what you are trying to do?

The BSS138 is about the nicest low Vgs(th) jelly-bean MOSFET I've seen. SOT-23, 3.5ohms Rds(on), and only $.07 from OnSemi & Siemens--or only $.05 from Fairchild--for a reel from DigiKey. And I've got a few hundred in my possession. Kewl.

Ciss(max) = 50pF (Zetex), 27pF (Fairchild) -- not terrible. By comparison, Fairchild's 2n7000/2n7002 Ciss(max) = 50pF, Vgs(th) (max) =

3v @ 1mA.

Cheers, James Arthur

Look at Philips ...UN series. They are spezified at 1.8 V VGS

--
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

ON Semi's NTA7002N seems attractive on the surface - Vgs(th)=1.0v (100uA); Ciss 11.5pF. It looks like ~25mA @ 1.5v and 154mA @ Vgs=2.0v. $.04 in reel; tiny SC-75 package.

Is there a "gotcha" with this one that I'm not seeing?

I'm not deperate enough to pay ON $11 to ship a "free" sample yet :-), and I'm not quite ready to buy a whole reel.

Curiously, the SOT-23 version from ON has very different specs. I'd have thought they used the same die for both, but the package alone can't account for these differences, can it?

The SOT-23 version Vgs(th)=1.0 to 2.5 (@ 250uA); Ciss is 50pF; it'll do

115mA, but at Vgs=8v.

In article , linnix wrote: [...]

This is not true. If you buy 1000 transistors from 1000 different batches they will average somewhere near 2.1V. The ones they make on Tuesday morning will be more tightly clustered around some other number.

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Uwe Bonnes =E5=AF=AB=E9=81=93=EF=BC=9A

Hi

Could you please help to provide the link? Thank you very much.

because I can't find it...

here is the link I found:

I can see rf / power mos only ....

Best regards, Boki.

Do you mean these guys?

I think they are too new to have a stable price yet.

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[....]

1mA at 1V

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linnix =E5=AF=AB=E9=81=93=EF=BC=9A

rent

rn

Hi,

Here is the circuit I am going to do: ( I want to replace transistors )

Here is the model

Simulation result:

It seems that the Vgs is about 3V, I don't know why it is about

2=2E4V..., could you please advice?

Thank you very much.

Best regards, Boki.

Ah... maybe the fact that everyone's got it on 25 week leadtimes...

However, these also look interesting and are in-stock in cut tape from Digi-key, though at 2-4x the cost:

Vgs(th)=1.0; 11.5pF; 238mA:

Vgs(th)=0.76v; 110pF; 915mA:

I like the small package (SOT-23 is awfully gigantic these days, isn't it?), and the reasonable price. That part's typical Vgs(th) is spec'd at 1.0v @ 100uA, but it's 1.5v worst-case, versus Fairchild's BSS138's Vgs(th) of 1.5v @ 1mA, worst-case, so the BSS138 comes on harder, earlier (i.e. at lower voltages).

Ciss is only 12pF (typ) @ 5V Vds, beating the BSS138's 27pF (max) handily.

Nice part.

James Arthur

That's a monster! SOT-89, Ciss = 110pF!

Cheers, James Arthur

No, D2PAK, Ciss = 2000pF is an monster. Perhaps its a "monsteret".

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