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Which MOSFET do I use?

Discussion in 'General Electronics Discussion' started by grom, Mar 21, 2013.

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  1. grom

    grom

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    Dec 5, 2010
    I am looking for a mosfet with a low Ron for making a phase sensitive detector for low voltage (nV-mV) signal switching and was wondering if anyone has used or can give a suggestion on what to use. For switching, The gate goes from -16V to +12V to transfer a low voltage AC signal from source to drain with Ideally no drop in Amplitude. nMOS preferred with a TO-220 package.
     
    Last edited: Mar 21, 2013
  2. BobK

    BobK

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    Jan 5, 2010
    A MOSFET is not useful for AC voltages. They generally have a diode that conducts all the time in the reverse direction. I think what you are looking for is an analog switch. Also, unless you are drawing signficant current at that voltage you want to switch, you would not need a very low Ron. Tell us what you are trying to do.

    Bob
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    At nV or mV the reverse diode will not conduct, so the mosfet can be used for an AC signal. And the voltage drop is proportional to current, so unless these are high current signals, the Rds(on) is going to be of no significance.

    And TO-220 package to switch mV signals? -- that's really weird.
     
  4. grom

    grom

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    Dec 5, 2010
    Basically what I want is shown in the image. The Package doesnt really matter as long as it is general PCB compatible and not surface mount.
     

    Attached Files:

  5. BobK

    BobK

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    I was assuming mV meant up to 1V, so the diode could be a factor if I was correct. On the other hand, I think small signal MOSFETs do not have a body diode, right? I still think an analog switch will do exacly what he wants and is designed for this purpose.

    Bob
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    And I assumed that mV meant < 10mV (especially when paired with nV).

    And the OP has not provided enough information.

    Correct. And I remember when mosfets came in small metal packages with 4 leads and a shorting strap. But try to find a non Power Mosfet these days.

    I think you're right. (So a 4066 or 4016.) If not, a 4007 provides access to several CMOS mosfets with a body (substrate) connection not tied to the source
     
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