Limiter/ Attenuator designing

Discussion in 'The Projects Forum' started by kahafeez, Dec 2, 2008.

  1. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
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    Hi, i'm working on a project and i need to change the voltage levels for some devices.... for increasing the level i use opamp bt how to decrease the level... say a device gives 5Vpp as output bt the device next to this only accepts 400mV signals.... so how to achieve this? plz help and tell me some general solution bcz i need to do this at alot of places not just this case bt at other places too.... thanks

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  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You need an AGC (Automatic Gain Control) circuit.
    This is a circuit that looks at the output and regulates it as the input changes.

    Greetings,
    Bertus
     
  3. steveb

    Senior Member

    Jul 3, 2008
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    469
    Why do you say he needs an AGC circuit? Why can't he use a simple OPAMP based attenuator? For example a voltage divider with an OPAMP buffer. He says the input is 10V p-p and the output is 0.4 Vp-p. If the input level is known and relatively fixed, then the AGC would be overkill.

    If the input level is changing (or has the possibility of changing), then the AGC is clearly the way to go.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    You can use an inverting op amp configuration with a voltage gain of 0.08 (0.4/5). This will invert the signal, so it will work if it doesn't matter if the signal gets inverted.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,647
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    Hello,

    In the text he says 5 Volt, in the drawing he says 10 Volt.
    When you make an AGC it doen't care what you send in to get 0.4 Volt out.

    Greetings,
    Bertus
     
  6. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    As you can tell from the responses you need to provide more information for a specific solution to your task. If the input voltage level changes over time then you need some kind of AGC circuit to keep it's output consistent at all times with a changing input level. However if the input signal is a fixed level but just too much, then you might be able to just use a simple resistance voltage divider. Would also be helpful to know the source impedance and the load impedance to reach a 'perfect' solution.

    Good luck
     
  7. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
    150
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    i found the solution. i'll use an op amp 741 and i'll set the gain between 0 and 1 whatever my application requires. that will solve my problem with the least effort. the resistive divider wont work for AC. its for DC
     
  8. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    "the resistive divider wont work for AC. its for DC"

    Resistive dividers are just as effective for AC as DC, what do you mean by that?
     
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Resistive voltage dividers work well for both DC and AC voltages.
     
  10. kahafeez

    Thread Starter Active Member

    Dec 2, 2008
    150
    0
    oh yeah man. u people are rite..... actually someone told me that resistive divider wont work for AC. bt i did a simple simulation and it did work. thanks guys..... thanks alot
     
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