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Need help modeling IF transformer in LTspice

Discussion in 'Radio and Communications' started by joeh100, Aug 4, 2014.

  1. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    You can reverse the transformer.
     
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  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Intuitively, never stated.
    Back in post #13 I have the two windings at 208uH and 135uH which is 1.54 like you say. I agree in the ratio but not on the value. The values do not add up to 680uH
     
  3. Tsif

    Tsif New Member

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    forgive me it's an habit.

    thanks alec_t.

    I prefer to re-write this post here:

    Sorry it's the first time that I will use the IF transformers. Can I reverse primary and secondary when I use the transformer? And again thanks to ronsimpson for his explanation. :)
     
  4. dave

    Dave New Member

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  5. Tsif

    Tsif New Member

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    Thanks a lot :)
     
  6. BobW

    BobW Active Member

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    Something that may have been overlooked is that the coupling coefficient in an IF transformer is considerable less than one, and I don't think anyone mentioned that. (I read through all the posts rather quickly so I may have missed it.) That will affect the inductance seen on one side of the transformer due to the inductance on the other side.
     
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  7. Tsif

    Tsif New Member

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    Hi every one,

    I don't know if I must create a new post for this question because there is still a link with this title and I will write it here.
    This is my problem:

    abcTransmitter.png

    I want to have 2.5V peak to peak at the output of the transformer (on point C). On point A I have 3.3V and on point B I have a signal 120mV an in the output I have 12mV. I think reverse the primary and secondary is the solution but it isn't. Please I need a help. Thanks
     
    Last edited: Mar 13, 2017
  8. JimB

    JimB Super Moderator Most Helpful Member

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    Looking at the turns ratio, I would expect those voltages.

    Can I suggest that you tell us what it is that you are trying to do.
    Just tell what you want to do, not how you incorrectly think the problem should be solved.

    Going around in circles trying to make some bad idea work the way that you think it should, is usually a waste of time.

    JimB
     
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  9. Tsif

    Tsif New Member

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    Thanks for your answer JimB. So I want to creat an transmitter PLC, I want to use 455KHz as frequence; And I want to creat an coupling circuit with IF transformer. :)
     
  10. JimB

    JimB Super Moderator Most Helpful Member

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    PLC?
    Programmable Logic Controller ?
    or
    Power Line Communication ?

    JimB
     
  11. Tsif

    Tsif New Member

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    If you look at the circuit you will decode so easily that PLC means here Power line communication. :)
     
  12. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    To talk on the power line you need to reduce the 50/60hz signal, and 100/120hz noise.
    Your 455khz signal might be 0.1 volt while the power line is 220V or 110V.
    I added a high pass filter (R3, C3) that will reduce the power line frequency.
    upload_2017-3-13_19-10-10.png
    upload_2017-3-13_19-11-4.png
     

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  13. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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  14. Tsif

    Tsif New Member

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    Sorry for the answer very late, because I was in the countryside, and I haven't internet.
    Thanks ronsimpson.

    I want to use the IF transformer for galvanic isolation for the transmitter and I don't know how to branch it. For the receveir I think it's OK. And for all the circuit that you suggest to me what kind of transformer are the circuit used? thanks a lot. :)
     
  15. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Are you sure the transformer insulation and coil separation are rated for line voltage? IF transformers are normally used at low voltages only.
     
  16. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Look at some of the schematics I provided. Some use two small high voltage capacitors to isolate from the power line.
     
  17. Tsif

    Tsif New Member

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    thanks alec_t; yes I know IF transformer is for low voltage; Or if I can eliminate the 50Hz (220V/50Hz) I can use IF transformer. I thik I can use an RC high pass filter to incrase the 220V :) .
     
  18. Tsif

    Tsif New Member

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    Thanks ronsimpson. :) do you know what kind of transformer I can use if I want to replace the IF transformer? is an smps transformer an solution? and where I can find an smps transformer? thanks a lot.
     
  19. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Here is a "pulse" transformer. Primary to Secondary voltage can be as high as 1500 volts.
    330uH but not adjustable like the IF transformer. So you will have to put a capacitor across it. Then maybe adjust the cap a little to get the frequency right.

    Look at pulse transformer; Usually 1:1 turn ratio but some are different. Look at the insulation voltage.
    I found this one at digikey.com but most parts supplies will have them.
     

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