calculation of slew rate practically?

Discussion in 'Homework Help' started by SNVHKC, Jun 28, 2012.

  1. SNVHKC

    Thread Starter New Member

    Jun 28, 2012
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    could some one please suggest a way to calculate slew rate of op07 practically in laboratory?
     
  2. steveb

    Senior Member

    Jul 3, 2008
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    If you do it in the laboratory, then strictly speaking, it's a measurement and not a calculation. If you just want a simple method, then you can wire up a simple unity gain buffer amplifier and put a step change in voltage into the input of the circuit. Make sure the rise time is much faster than the slew rate estimate you get from the datasheet. The output will ramp up initially and then will eventually go to the correct constant value of your step voltage. The slope of the initial ramp is the slew rate.

    Another way is to use a function generator to put triangle waves into the buffer circuit. With a dual channel scope, overlay the output and the input. The output will track with the input at low frequency, but as you bring the frequency up, eventually, the output will not track and the amplitude will be lower and the slope of the triangle wave will be limited by the slew rate limit. The slope of the output triangle wave, when you are beyond this critical frequency, will be the slew rate limit.

    If you don't see nice straight ramps, then this means there is nonlinearity in the opamp which is more complicated than a simple slew rate limit.

    Generally, you will want the amplitude of your test signals to be a relatively large percentage of the power supply limits, otherwise you may hit your bandwidth limit before you hit your slew rate limit.

    The OP07 has relatively low bandwidth and small slew rate limit, so the measurement should be easy with any typical O-scope (analog or digital) and inexpensive function generator.
     
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  3. crutschow

    Expert

    Mar 14, 2008
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    Just to be clear, the calculation part of the measurement is to divide the delta voltage of the slew part of the output waveform by the time the slew takes.
     
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  4. SNVHKC

    Thread Starter New Member

    Jun 28, 2012
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    What is the magnitude of the step signal i should give to my buffer?sorry,i couldn' understand that properly.
     
  5. steveb

    Senior Member

    Jul 3, 2008
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    Anywhere in the 1 V to 10 V range should be ok, provided you are using +15 VDC and -15VDC as the power supplies.
     
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