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adding an AC level (~1V 3KHz Sinus) on a DC level (30 to 100 V) line

Discussion in 'Electronic Design' started by jsmith, Apr 19, 2007.

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  1. jsmith

    jsmith Guest


    I will be appreciated with your comments and suggestions for adding an
    level (~1V 3KHz Sinus) on a DC level (30 to 100 V) line.
  2. D from BC

    D from BC Guest

    Possibilities are:
    1) A transistor common emitter amplifier
    2) resistor network
    3) transformer
    4) RC circuit
    5) summing amplifier

    D from BC
  3. John Fields

    John Fields Guest

    Assuming you mean "add" as in "algebraic summation":,
    view in Courier:

    .. |
    .. [C]
    .. |
  4. What impedances are you talking about? Or you'd better tell something about
    the application. Crucial for a usefull advice.

    petrus bitbyter
  5. jsmith

    jsmith Guest

    impedance is about 1 MegaOhm
    piezo driver
  6. Eeyore

    Eeyore Guest

    What impedance is the DC line ?


  7. Transformer couple the signal to the DC voltage. AKA "Modulation

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  8. Don Bowey

    Don Bowey Guest

    The most easy approach will be to use audio transformers having a split line
    side. Put a non-polarized cap (1 or 2 mFd.) across the line-split leads of
    the transformers (usually called the A and B leads). Put the dc voltage on
    the A and B leads at one end of the line. Put the 3 kHz signal on the
    primary of the transformer. At the other end of the line receive the dc on
    the A and B leads, and the 3 kHz signal ar the transformer secondary.

  9. It may be a megohm at DC, but I'll bet a dollar it is lower
    at 3kHz. What is the capacitance of the piezo device?
  10. jsmith

    jsmith Guest

    I should measure capacitance of output long cabel and piezo, but it
    will be less than 1uF
  11. Phil Allison

    Phil Allison Guest


    ** Better not apply 100 volts DC direct to a piezo driver - it will blow
    it up.

    ........ Phil
  12. jsmith

    jsmith Guest

    it is a piezo valve and its work range is up to 100V
  13. Small transformer secondary in series.

    On its primary for example a 807 tube amp or a trans-sister.
  14. Ah, a piezo valve ranging 30-100Vdc and a "impedance" of about 1M. That's an
    important piece of information. But, all piezo elements I'm aware of have a
    capacitance too. That capacitance needs to be charged/discharged when
    switching on/off *and* it is much lower an impedance then 1M for a 3kHz
    sine. The line will have some impedance (mostly capacitive) too, highly
    depending on the type and length of the wiring used. On the other side of
    the line you will have a 30-100Vdc power source which also has an impedance.
    Depending on the type it might even be a shortcut for the 3kHz sine. (Some
    47uF smoothing capacitor for instance). That 3kHz sine source will also have
    some (output) impedance I guess. So I still can't give an appropriate answer
    to your question.

    petrus bitbyter
  15. It had better be. If the total capacitance were 1 uF, the
    impedance at 3 kHz would be 53 ohms. It will make a lot of
    difference to the driver if the total capacitance is 100 pF
    or 1000 pF.
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