What type of switch should I use in my circuit ?

Discussion in 'General Electronics Chat' started by DRAGOS-GEORGEL GOGU, May 10, 2016.

  1. DRAGOS-GEORGEL GOGU

    Thread Starter New Member

    Apr 25, 2016
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    I put red box where I want to use an analog switch.
    Any idea?
     
  2. Marley

    Member

    Apr 4, 2016
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    40
    I assume you only want 1 of the 3 resistors to be selected at any time.
    There are plenty of devices available. Have a look at the Maxim MAX309.
    This is a dual 4-channel multiplexer.

    If you are using this to switch the gain of your circuit, note the "on" resistance of the switch and take this into account.
     
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  3. George Gogu

    New Member

    May 6, 2016
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    Thanks!
    Seems to be very useful the MAX308_MJE.
    I'll try to find a library and hope to use the multiplexer in short time.

    Thank you again!
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,984
    3,223
    Here's a couple of interesting switched gain configurations where the switch resistance has no significant effect on the gain since little current (only the op amp input bias current) goes through the switch (as long as only one switch is closed at a time).

    One downside is that the calculation of the gain resistor values for the desired gain is a bit more complicated.

    Also the input impedance for the inverting configuration will vary with the gain setting, but that shouldn't be a problem as long as the input is being driven by a low impedance source, such as another op amp output.

    upload_2016-5-10_9-23-58.png
     
    Last edited: May 10, 2016
    DRAGOS-GEORGEL GOGU likes this.
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