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AC Voltage Amplifier

Discussion in 'General Electronics Discussion' started by Turtle44, Apr 24, 2015.

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  1. Turtle44

    Turtle44

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    Apr 24, 2015
    Hello,
    I am trying to take a 10 kHz 10VAC signal and amplify it to around 100VAC. So far I have looked and the common base amplifier appears to be the best option for me since transformers only handle a fixed frequency range. However in LTspice this is giving me a square wave and no negative voltage. Does anyone have any recomendations to fix this? Untitled.png
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    how far from 10kHz is the freq likely to vary ?
    at that low freq an appropriate transformer will have quite a wide range
     
  3. duke37

    duke37

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    Jan 9, 2011
    The 2N2222 is listed at 60V top whack. 100V will do it no good.
    You are overdriving so that the transistor is turning fully on and fully of so generating a square wave.
    You do not have a negative supply so how do you get a negative voltage?
    A symmetrical output waveform could be obtained by feeding the output through a capacitor.
     
  4. Turtle44

    Turtle44

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    Apr 24, 2015
    10-200kHz would be the full range. Okay duke, so I tried another transistor that had a higher voltage value (I didn't see a whack value in spice but the Vceo was 30 so I picked one with a Vceo at 150), added a capacitor, and tweaked the resistors. The capacitor made a big difference! This looks so much better already. Could you clarify what I can do to make the wave more like the signal or at least make the peaks and troughs equal in duration? Also I had to change the input DC, which isn't a big deal but I would like to know why that works. number5.png
     
  5. HellasTechn

    HellasTechn

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    Apr 14, 2013
    That is right.
    Can not agree more !!!
     
  6. Turtle44

    Turtle44

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    Apr 24, 2015
    Update:
    I have been searching around and I found this circuit also. However, I do not know if LTspice is correct in saying this would work for 10-200 kHz. Can anyone confirm or should I stick to the previous circuit? trial2.png
     
  7. BobK

    BobK

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    Jan 5, 2010
    That is a much better circuit. It is a standard common emitter amplifier. Common base is normally used for current amplification with very low input and output impedance. If LTSPICE shows it working it is likely to work reasonably well when built. Note that the output impedance is going to be quite high. What are you planning on driving with this? You might want a push pull output stage if you need significant power out.

    Bob
     
  8. Turtle44

    Turtle44

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    Apr 24, 2015
    Itl be used to make a small electric motor so I only need the fields to act on a wire (there'l be four of these outputs alternating in sequence). That wouldn't be high impedance would it?
     
  9. Turtle44

    Turtle44

    7
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    Apr 24, 2015
    Hey everyone,
    So I am still trying to amplify a 10-200kHz signal from 10VAC to 100VAC. My professor suggested this op amp (PA107DP, http://www.digikey.com/product-search/en?vendor=0&keywords=PA107DP ) and I have read about how they work but I can't make a working schematic in ltspice. The part isn't in the program but I have tried with the LT1001 in a non-inverting amplifier to no avail. Is there a simple circuit out there for this?
    Untitled3.png

    Pin # Pin name Description
    1 IN Summing Junction Input for Inverting Operational Amplifier
    2 +VAUX +10V to +18V Supply for Input Circuits
    3 -VAUX -10V to -18V Supply for Input Circuits
    4 GND Ground
    5 Open Pin
    6 Open Pin
    7 Open Pin
    8 +VS +20V to +100V Supply for Gain and Gate Driver Circuits
    9 -VS -20V to -100V Supply for Gain and Gate Driver Circuits
    10 -VSP -20V to -100V Supply for Output Source Follower
    11 OUT High Power Output of Amplifier
    12 +VSP +20V to +100V Supply for Output Source Follower
     
  10. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Are you trying to power the opamp from 100 Volts?
    Adam
     
  11. Turtle44

    Turtle44

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    Apr 24, 2015
    From what I understand, I'm using the 100V to limit how much it will amplify the 10VAC signal
     
  12. davenn

    davenn Moderator

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    Sep 5, 2009
    you cant power the Op-Amp from 100V, its rated at 18V max !!

    and I have moved the posts to this thread to keep it all together and save confusion
     
  13. Arouse1973

    Arouse1973 Adam

    5,164
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    Dec 18, 2013
    Why have you changed from what looked like a working circuit using the BJT. And is your professor going to buy one of those op-amps at over $400 each? :)
    Thanks
    Adam
     
  14. BobK

    BobK

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    Jan 5, 2010
    Well, the working circuit was not a power amplifier. This one is. But a bit expensive as you note.

    Bob
     
  15. Turtle44

    Turtle44

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    Apr 24, 2015
    Yes, she will be buying it. She thinks the op amp will be something we can put in.
    Yes, she will be buying it. She thinks the op amp will be something we can put in. I mean ~10 VAC will go into the amp and be raised to 100VAC. So I was reckoning that I could put the AC signal through +VAUX and -VAUX somehow, and supply 100V to the +Vs and -Vs. Would this be the correct usage of it? Also I would be using the recommended capacitors from the data sheet.
    Thanks for the help guys!
     
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