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Op Am Gain Max400

Discussion in 'Electronic Basics' started by Mike Blankenship, Feb 16, 2004.

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  1. I have a 2 stage circuit. The 1st stage is a basic Voltage follower that
    works good. It out puts
    100mv. My problem is with the second stage which I am trying to gain by 10

    Stage 1 >>>> 100mv
    Stage 2 MAX400

    Pin1 Vos Trim Not used
    Pin2 -IN
    Pin3 +IN
    Pin4 V- (GND)
    Pin5 NC
    Pin6 Vout
    Pin7 V+ (5V)
    Pin 8 Vos Trim Not used

    Pin 6 (vout) is connect to Pin2 (-IN) with a 100K resistor. Pin2 (-IN) is
    connected
    to ground via a 10K resistor. This should give me a gain of 10 and I should
    see a
    Voltage of 1Volt at the put put Pin6 (Vout)

    I have a clean signal going into Pin3 (+IN) of 100mv .. ~5mv noise. The
    output always reads ~
    4.85 volts. Any insight would be appreciated.

    Thanks

    mike
     
  2. kansas_ray

    kansas_ray Guest

    The gain is actually 11 (1+100K/10K) but this is not your problem.

    The MAX400 is only rated down to +/- 3V on its supplies. You are trying to
    run it on a single +5V supply and ground.

    If you have a -5V supply, connect it to pin 4 (after removing ground) and
    see what happens.

    Regards,
    Ray
     
  3. I was using an OP-Amp whic did not have rail to Rail Inputs. I was tring to
    measure 200mv
    But the Common mode range was above 1 Volt on the lower end.

    Thanks
    all for the input
     
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