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universal buffer/modulator cct

Discussion in 'General Electronics Discussion' started by julesison, Nov 30, 2015.

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  1. julesison

    julesison

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    Nov 30, 2015
    hi, and of course my first line has to be to apologise for my ignorance and secondly the possibility that this has been covered somewhere i couldn't find it.
    i need to have a signal generator drive any number of different hf diy transformers that i want to experiment with. so i don't know what impedance the cct has to match only that the frequency will be from 20khz to 100khz max. is there not a "universal" impedance matching, "buffer" type device?
    i attach a rough pic of what seems to me the perfect "cct". it would be basically a cct that allowed a signal generator to "modulate" the dc from a bench top power supply. for the sake of convenience it wouldn't have to swing + and -, it could be a square or sine all above zero. the power supply can be the current limiter through it's current output adjustment. i just need something that shows a high impedance to the sig gen output and that doesn't care about what's connected to it's output as it's current limited via the power supply anyway. surely this is the easiest way to be able to test "any" winding/transformer? sorry again if my simplistic approach is off but logically it seems sound?
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Why do you need matched impedance? And have you considered the impedance vs. frequency characteristic of any transformer when operated ver a 1:5 frequency range?
    Depending on the kind of experiments you want to perform you may simply life with mismatched impedances and if necessary correct the results of your experiments to account for the mismatch. Once your experiments are done and you have, I assume, found a combination of compponents that works satisfactorily you can still build a buffer that matches the impedancce of the final circuit to optimize performance.

    Any amplifier with voltage input will suffice. A search for "a00kHz amplifier", for example, turns up a wide selection.

    This sounds unreasonable. When you drive an amplifier such that the output is limited by the power supply, the wavefrom will be distorted aas soon as the limiter sets in. Also, the amplifier's built-in feedback loop may saturated which can lead to additional distortions when the amplifier (or power supply) comes out of saturation. There's also the issue of which current you want to limit: peak current or effective current? A good amplifier can deliver much more peak current than effective current while still operating within its design limits. But a current limited power supply would limit peak current when there is still room for the amplifier to deliver more effective current.
    Better look for an amplifier that has built-in overload protection.
     
  3. julesison

    julesison

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    Nov 30, 2015
    all i wanted was something that could "sit" between a signal generator and as yet unknown series of transformers/windings and allow the signal generator to feed the windings without being overloaded. i appreciate your superior knowledge but as i said my knowledge, in this field, is limited. the voltage will be 3 - 12 volts at 100-300 mA and all transformers/windings/placements will be tested using the same parameters, so any distortion/clipping etc will be the same for all. is what you're trying to say "go for an audio amplifier with headroom and short cct protection"?
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Short circuit protection: yes
    Audio amplifier: no. An audio amplifiers will not work well above ~30kHz.

    This application note shows a comparatively simple amplifier that is good up to 100kHz, but without short circuit protection. You can always add a series resistor between the amplifier and the load to limit the current.
     
  5. julesison

    julesison

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    Nov 30, 2015
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Your original request was 100kHz, Also note that 65kHz is the -3dB corner frequency, this is where outpuit power is 1/2 of the max. power in the pass band.

    If you're willing to invest as much, I think there are better or less expensive amplifiers for this purpose. Look e.g. at this one. It is "rated" at 100kHz (also without giving away the attenuation at that frequency) and it includes overload protection.
     
  7. julesison

    julesison

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    Nov 30, 2015
    sorry meant to say i had amended the top frequency to 50khz
     
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