Opamp to amplify signal and then send it to a step up transformer

Discussion in 'Analog & Mixed-Signal Design' started by Leo Silver, Aug 12, 2016.

  1. Leo Silver

    Thread Starter New Member

    Apr 27, 2016
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    Hi all,
    I would appreciate your help with a project I am having. I want to implement a supplier that will take a signal form a signal generator amplify it and send it to a step up transformer. The more I try to understand the more complex it gets and here is why I need your help!
    So in simulations there arent any difficulties just to take the signal with an opamp (x10 amplification) and then send it to a 1:50 step up transformer. The signal is a 5Vpp sinusoidal. But from simulations to practice there are always complications.
    Could you highlight to me the main spots that I should take care. Also I cannot find any HV transformer to order. All I find online is for mains voltage input to some more volts 240/480 lets say. My current model gives an almost 3kV voltage output.
    Also, what about impedance matching in the primary and secondary? Where should I get started with?
    I will appreciate anyone's help and I am very willing to first understand in depth before I go to implement it so bare with me and hopefully with your help I ll get there.
    Thank you :)
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    50 times 5V gives 250V not 3kV?
    How much current do you want from the transformer output?
    To get 3kV you might consider a piezo transformer for low currents.
     
  3. Leo Silver

    Thread Starter New Member

    Apr 27, 2016
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    The 10Vpp signal (5Vmax) is going to the amplifier x10 so you get a 50V output. The current from the transformer output is minor uA since the load is of high impedance. Thanks for your answer. Is there a particular reason besides current to use this type of transformer? Also as I see the gain of the PZT varies with the frequency driven and this wont work for me as I want a broadband transformer. I need to use a variety of frequencies in the kHZ to MHz range.
     
    Last edited: Aug 12, 2016
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Hmm... I think you are going to struggle to buy a 3kV rated transformer with a 1000:1 frequency range. Do you need the output to be a sine wave? Would a square wave or spikes do?
     
  5. Leo Silver

    Thread Starter New Member

    Apr 27, 2016
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    Last edited: Aug 12, 2016
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    There is almost no data in the first link, not even the ratio of the transformer, no frequency range, no inductances.
    The second link specifies a frequency range from 20kHz to 100 kHz, so it is going to be a problem at 1MHz+
     
  7. Leo Silver

    Thread Starter New Member

    Apr 27, 2016
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    I may not go up that high.. I searched a lot and I can't find something for my needs. Would it be easier if I build one myself?
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    What is the supply voltage to your op-amp?
     
  9. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Designing wide band transformers is far from trivial.
    Does it all have to come from one transformer? Could you do part of the range with one transformer then unplug it and plug in a different one?
    Switching 3kVAC is also far from trivial.

    It does seem to be a very high voltage op-amp, but compared to the transformer, that's much easier to fix.
     
  10. Leo Silver

    Thread Starter New Member

    Apr 27, 2016
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    I guess I could but it would be better if it was more compact. But this is an alternative :)
     
    Last edited: Aug 12, 2016
  11. ScottWang

    Moderator

    Aug 23, 2012
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    5V *10 *50 = 2500V, where is 3KV came from?
    5V input and using op amp to amplifying 10 times, that is 50V, ±22V power supply for LM741, that is only 44V, ±16V power supply for LM358 and LM324, that is 32V, so after op amp should be adding transistor to drive the transformer.
     
    absf likes this.
  12. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    If you can limit yourself to 30kHz or so, a standard audio amplifier will get you your intermediate signal. Feed the amp with a line-in (~2.8V p-p) signal and the output will be in the tens of volts and can drive the low impedance primary of your transformer.

    You can get such an audio amp very inexpensively. It will be far superior to a DIY solution unless you want to spend a lot of time on it.

    If you really want >100kHz, never mind.
     
    absf likes this.
  13. #12

    Expert

    Nov 30, 2010
    16,338
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    How about you back up and say why you think you need a megahertz sine wave at kilovolts?
    A lot of people come here saying what they want when it isn't what they need.
    The fact that you can imagine or, "simulate" a wide bandwidth kilovolt transformer doesn't mean they exist in the physical world.
     
  14. Leo Silver

    Thread Starter New Member

    Apr 27, 2016
    26
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    Thank you all for your answers. I gave some ranges of values that I would like to achieve and I dont get why people are stuck in the 3kV thing. 2.5kV is what I get yes you are right but I dont want to have a tranformer operating at its maximum and of course I have thought whatfor I need what I need. There are different approaches to a problem and I am try to find the one that suits me. As a first step I won't go higher than 20kHz as there are other compications to my application beside the transformer. Thanks again for keeping the post updated with your interesting ideas.
     
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