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Normally Closed CMOS Switch without power

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zula

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Hi guys,

I need a cmos switch that will shorted input to output(NC) while there is no power(VCC). I dont know is it possible? Normally we can do this with relays but we dont prefer to use relays in our projects. If you can suggest me some components i will be very happy.


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ravindragudi

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Information about the application is missing and this will be difficult for others to provide you proper response.

Review some solid state relays like CPC1017NTR. These may fit your requirement.
 
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zula

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dear ravindragudi,

Thanks for your reply. Basically there are two communication line have to be connected when there is no power. When the power is on, MCU unit will break this connected lines and doing something.

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FvM

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As far as I'm aware of, CPC1017 is a regular NO solid state relay, but NC types are available as well, e.g. Vishay CPC1017.

B.t.w., entering "normally closed solid state relay" at Google would have revealed some of them. Technically, the question refers to building a MOS or CMOS switch with depletion mode FETs which are a bit outside the usual CMOS processes, but can be made.
 
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ravindragudi

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In my previous post I just suggested a kind of SSR and left to zula to see if such SSR can be used. That was a NO as said by FvM. It is called Form-A SSR.

The NC SSR is called a Form-B SSR. These are also available. Below are some examples -
CPC1106N (http://www.ixysic.com/Products/SSRFormB.htm)
LH1501BAB (http://www.vishay.com/docs/83805/lh1501ba.pdf)

I have never tried Form-B of SSR so it is better if you try it out in a breadboard circuit and then decide on its use.
 

zula

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Hi All,

Thanks for replies. But as i said we dont prefer doing this with relays because of cost issues. If there is no alternative solution of course we will use relay. But at this point i will continue my researches.

Dear FVM,

Are you saying that depletion mode fets can be useful for my application. I think i didnt understand exacly what you are meniton about.


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erikl

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Instead of a depletion mode MOSFET (which are rare) you could perhaps use a JFET. Without power these are NO.

NC of course, sorry!
 
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crutschow

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Here's a manufacturer of N channel depletion mode MOSFETs.
The require a negative Vgs to turn them off.
If you want the device to turn off with a positive Vgs voltage you could use a P-Channel JFET.
 

FvM

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Depletion mode MOSFET are also available from Infineon. If I understand right, zula wants a ready-made normally closed solid state relay. Several suitable devices have been suggested in post #4 and #5, in so far I think that the original question has been solved.
 

zula

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Hi,

Actually my requirement is really simple. I need to NC device without power. And it should be very cheap. I know that i can design my circuit with SSR but i didnt prefer it. At this point i think there is no MOS device that NC without power. So i will go with SSR.

Thank you for all your respones.
 

FvM

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It's possible with the previously mentioned depletion mode MOSFET or JFET.
 
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asdf44

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Yes, depletion mosfets and Jfets as other people mentioned do exactly what you want...

How much current does it need to handle when un-powered? Will the applied voltage be in both polarities?
 

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