Need help with a bi-phasic signal amplifier

Discussion in 'Analog & Mixed-Signal Design' started by JBee, Jul 13, 2016.

  1. JBee

    Thread Starter New Member

    Jul 13, 2016
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    I've been pulling my hair out trying to figure out a way to amplify a signal to achieve a 58v peak to peak bi-phasic output.
    That said, I found a old schematic for a plant growth stimulation dating back in '98, which appears to have the output I'm looking for, however, as it is based on an oscillator circuit, this doesn't allow to control the wave type and frequency.

    And so my idea was to reconfigure the amplifier section to receive a signal from a source such as a signal generator, so as to create the type of wave and frequency I need while maintaining the bi-phasic properties of existing circuit.
    Unfortunately, this is beyond my limited realm of understanding of op-amps and so I'm hoping someone here can help with some pointers on what changes I'd need to do, to achieve my goals?

    Example of output I'm looking for:
    [​IMG]
    Example of the input I'm looking trying to achieve:
    [​IMG]

    That said, if anyone could lend a hand with this, I'd be most grateful.
    JohnB

    PS. apparently, I cannot place two images in the same post :(
     
  2. JBee

    Thread Starter New Member

    Jul 13, 2016
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    Second image because initial post will not accept two images;(fixed)
     
  3. JBee

    Thread Starter New Member

    Jul 13, 2016
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    please remove :(
     
  4. #12

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  5. JBee

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    Jul 13, 2016
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  6. #12

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    You started with op-amps, 741 and 358. You want at least 58 volts peak to peak...all the op-amps on that page will do that.
    They can output anything from 0.05 amps to 10 amps.
    What more do you want?
     
  7. JBee

    Thread Starter New Member

    Jul 13, 2016
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    I'm looking to create a bi-phasic output (180° offset) @ 58v
    That said, the first illustration does this, though it does not allow for a variable input (fr. signal gen)
    The second circuit(illustration) allows for a signal gen input, though is not producing a bi-phasic output.
    My hope is to modify the first circuit to allow signal input(frequency generator) to produce a bi-phasic(180° offset) 58v peak to peak output.

    And so my objective to to convert the first circuit so that I can use a signal generator as waveform source instead of the oscillating circuit that is shown.
     
  8. #12

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    Define, "bi-phasic".
    2 outputs out of phase?
     
  9. #12

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    This vendor does not sell a dual op-amp that can go to 60 volts. Use 2 of them.
     
  10. JBee

    Thread Starter New Member

    Jul 13, 2016
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    Yes, exactly, as illustrated on the scope in the first image.
    Two outputs(ie, dual op amp package) @ 28v p/ch. 180° out of phase with each other (bi-phasic)

    PS. I have LM358P's which should qualify the task as each amp only needs to output >30v
     
  11. #12

    Expert

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    So, you want a dual op-amp in one package that can do 60 volts peak to peak.
    Use the parametric search engines at Jameco, Digikey, Allied, and other vendors.
     
  12. JBee

    Thread Starter New Member

    Jul 13, 2016
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    I already have dual op amps that can do this and so I don't need to order anything else at this time.
    What I do need however, is help modifying the schematic to allow a signal gen. input(vs the analog oscillator) and inverting the phase 180° on one of the op-amp outputs.
     
  13. #12

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    This is one way to do it:
     
  14. #12

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    Here's another way:
     
  15. JBee

    Thread Starter New Member

    Jul 13, 2016
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    Hello again #12,
    And thanks again for your help with this.
    I chose your second sketch as it appeared to be less work in contrast to one of my existing attempts. And so here's what it looks like;
    [​IMG]

    Which appears to do the trick when I run a square wave input, though I'll end-up with two different waves whenever I change this(see-saw, sine etc). And so my guess is that the resistors used in the feedback loops which are clearly wrong, are causing this. Though, I am however seeing two inverted waves when I feed a square wave into the sim.

    PS. it appears as though R1 blew up upon running sim also - lol
     
  16. #12

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    The resistors merely set the voltage gain. You can input 1 volt p-p and get 50+ V p-p if you calculate them correctly.
    As for Simulating...I don't do that and don't see why people trust them when they are obviously handing out the wrong results.
    "Ohh...the circuit must be wrong because I cant simulate it."
    Simulators can be very helpful, or they can just be another layer of opportunities for mistakes.
     
  17. JBee

    Thread Starter New Member

    Jul 13, 2016
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    Thanks for the tips.

    I'll bring the design to a board shortly, though I have to say, Multisim has proven to be spot-on insofar as output goes, to date. ie, what I get from the scope is very close to what comes out on a physical scope and meter. ( +/- the tolerance). Though all in all, I'd say the sim saves me a ton of trial and error on the board to date. - knock on wood

    That said, when I run the sim prior to popping R1, I see channel 1 outputting 50v whereas channel 2 is showing 20v
     
  18. #12

    Expert

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    For the non-inverting you have set up a gain of 2. For the inverting amplifier, you have set up a gain of one.

    For Rf = R feedback
    Rc = R to common
    Non-inverting gain = 1 + (Rf/Rc)

    for inverting, gain is Rfeedback/Rin
    I think you should be in the range of 10k to 50k instead of 1k.
    Try for a 1 ma feedback current.
     
  19. crutschow

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    The maximum voltage rating of the 741C is ±18V so obviously you can't safely use the voltages shown in your simulation.
    You need an op amp with a higher voltage rating.
    That's one place where a simulation usually won't show a problem that the real circuit will likely have.
    Component voltage and power limits usually have to be determined by hand (LTspice will show component power but not limits, if requested).
     
  20. #12

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    My datasheet site is down today and I don't know if this chip is sufficient.
     
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