Best Universal JFET Switch

[row-she]

Hi there,

I'm looking for a JEFT transistor that needs to have very specific technical requirements.

I'd like to be able to use it in an universal switching enviroment, meaning,
i can't tell you what voltages, resistances or impedances appear at drain or source.
(because it would be different every time...)

The JFET should:

- have near to zero resistance when its 'on'
- have near to zero leakage when its 'off'
- be available as smd (preverably as th as well)

Time is not an important aspect, meaning it doesn't have
to be a fast switch.

Its hard to explain what exactly I need this for. Lets just say I need a switch
that can make a connection between two contact-points regardless of its
electronical surroundings (...if that makes any sense  )
...and unfortunatelly it does have to been as small as a smd transistor,
otherwise i'd use relays.

Does anything come to mind?
I'd be greatful for any suggestions.

Thanks & Cheers,

Andy

/* EDIT */

Doesn't have to be a JEFT - could be anything as long as its small and cheap 

[armdnrdy]

With the information that you have supplied...I believe that you can find what you need at any electronics supplier, on the shelf right next to these:

[R.G.]

ANR is correct. Your list of requirements rules out JFETs for the switching. No JFETs will do that.

Well, actually, one will. It's a Field Effect Transistor that uses the magnetic field, not the electrical field to make contacts work.

They call them "relays". Even these have some limits, and must be thought about. None of these will work properly in all conditions where they may be given any random set of voltages and currents of any unspecified - and different each time! - nature.

I guess another way to put it is that "a switch that can make a connection between two contact-points regardless of its electronical surroundings" does not exist.

[row-she]

  ... yeah I know... thought I'd give it a try.... bummer...

those unicorns look interessting though - do you use the horns to supply voltage? 

[armdnrdy]

... yeah I know... thought I'd give it a try.... bummer...

those unicorns look interessting though - do you use the horns to supply voltage? 

You have to consult the data sheet for the proper pinout.   

[row-she]

  thanks... thought I'd give this one a try, but there seems to be no pin-description...

[slacker]

You've said universal but presumably there are some practical limits as to what might be attached to it, maybe figure out what they are and there might be a solution.

[duck_arse]

I thought the horn was used to warn approaching traffic.

[GibsonGM]

What's this for, Row-She?  Not a homeland security issue, is it?    

Why not a BJT?   Now I am curious. 


Duck - on a unicorn, isn't the horn its built-in test point??

[thermionix]

Not a homeland security issue, is it?    

First thing that came to my mind!

[PRR]

> i can't tell you what voltages, resistances or impedances

You should have some clue.

30,000 Volts as in a car spark-plug system?

0.05 Ohms as in a car starter-motor circuit?

If you get outside 40V 20mA, MOS-FETs are more likely than J-FETs. However a single MOSFET typically has a back-diode. In bi-directional applications, this conducts when you don't want it to.

There are opto-coupled back-to-back MOSFET packs for some fairly arbitrary mild-power switching.

> it doesn't have to be a fast switch.

Then use jumper-plugs. I can re-patch a single connection in a second or two. My uncle could re-patch a large card-sort programmer in 10 minutes.

[merlinb]

The SST10x areused in mixing consoles by the thousand:
https://www.trendsetter.com/v/vspfiles/assets/datasheets/Linear%20Integrated%20Systems/J108,%20J109,%20J110,%20SST108%20SST109%20SST110_Series.pdf

[row-she]

hey guys,

thanks for the replies! And no, I am currently not working for homeland (or any other agency for that matter).
It was more of a crazy idea. Kinda already put an end to it. Should have been some kind of universal jumper,
that can be controlled via a microcontroller. I'd rather not bore you with the details (or embarrasse myself
while doing that  )

but again... thanks!

cheerio

[GibsonGM]

Oh, I wasn't implying you worked for them...I was wondering if someone should CALL them!   LOL   J/K   I'm sure you have a perfectly good project going and all.  No embarrassment, all ideas are worth looking at!     

Backstory:  I used to be on another forum, and every once in a while people would come in with non-specific requests like "I need to make a timer, and have it operate a capacitor discharge circuit....."  and they'd be hesitant to describe why they wanted it...VERY hesitant.  Always wondered how that worked out...

[row-she]

oh yeah.... that... now that you mention it.... i also need a scheamtic for something i can't tell
you what it is, but it has to count down from 30 once you apply 12v to it... 

[Hatredman]

i also need a scheamtic for something i can't tell you what it is, but it has to count down from 30 once you apply 12v to it... 

[armdnrdy]

Okay....so who's going to work up a board for this? 

[bluebunny]

Okay....so who's going to work up a board for this? 

Vero?  Dino, natch.   

[PRR]

me> There are opto-coupled back-to-back MOSFET packs

http://www.newark.com/vishay/lh1500at/ssr-mosfet-350v-150ma/dp/58K1788
http://www.farnell.com/datasheets/1809360.pdf
LH1500AT  MOSFET Relay, 350 V, 150 mA, 25 ohm, SPST-NO
$1.62

[antonis]

Okay....so who's going to work up a board for this?   

Definately my EAGLE library needs a refresment..