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Covert emitter follower to PNP

Discussion in 'Electronic Design' started by Jerry Norris, Jun 15, 2011.

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  1. Jerry Norris

    Jerry Norris Guest

    I have decided on this design and tweaked the rails to 9V and 3V,
    which still provides a nice 5V swing between 3V and 8V. Here is the
    Spice sim.

    To begin my project, I also need a PNP version that will run form -9V
    and -3V rails. IOW swing between -8V and -3V.

    I have played around with the components in LTSpice, but without much
    luck. There is nothing I can find on the net to work from.

    Can anyone please set me on the right track regarding what changes
    need to be made?

    Jerry Norris
  2. Jerry Norris

    Jerry Norris Guest

    Thank you for your reply. The output ground is in common with the
    input ground.

    The power supplies may or may not be referenced to ground. It seems to
    work either way. Yes, the 3V DC offset is a desired result.

    As stated in my OP I would like to produce a second matching circuit
    uisng PNP's where the ouptut swings between neg 3 and neg 8V, as
    opposed to pos 8V and pos 3V.

    I have tried a few things to no avail, and can't find anything similar
    on the net. Any expert advice on this would be much appreciated.

    Here is the link again.

    Jerry Norris
  3. If you replace all transistors by PNP types en revers all voltage sources it
    should have to work. If not, there's something wrong, probably with the
    simulator. Be aware that you cannot connect both inputs to the same source.

    petrus bitbyter
  4. YD

    YD Guest

    Late at night, by candle light, (Jerry
    Norris) penned this immortal opus:
    Whatsit supposed to do? Those DC sources are in floating anti-series,
    effectively making a single floating 6V DC source. Since they have no
    reference to the signal the whole circuit seems rather pointless.


    - YD.
  5. Jerry Norris

    Jerry Norris Guest

    Well, it's trying to work, but the output amplitude has dropped to 1
    volt and there is not the desired neg 3V offset I should have from the
    neg 3 and neg 9 rails.

    Any suggestions please?

    Jerry Norris
  6. Jerry Norris

    Jerry Norris Guest

    Yes, the output stage is floating at +6V. The negative of the two
    supplies could be tied to input signal ground, but I am trying to
    avoid that if possible.

    IOW I want to replace the input signal ground with +3V at the output,
    so the swing is between +3 to +9 without a common ground reference.

    Is everyone saying this is "pointless" because it can't be done, or
    because it hasn't been done?

    Jerry Norris
  7. Jerry Norris

    Jerry Norris Guest

    If I knew how to do it right, would I be here asking for help?

  8. Your simulater does not seem to function the same way in both cases. I
    suppose it has to do with the "ground" of your signal source that seems to
    have no relation to the rest of the circuit having the voltage sources
    floating. Guess the simulater chooses a common ground itself.

    petrus bitbyter
  9. Jerry Norris

    Jerry Norris Guest

    It seems to me there is a -6V potential between the -3 and -9V
    batteries. That is the power I want to use, not something referenced
    to an arbitrary ground, as in the inout signal.

    Jerry Norris
  10. Jerry Norris

    Jerry Norris Guest

    Sorry, but downloded all the messages on the above group and could not
    find a reference to this.

    Please advise how to view it.

    Many thanks,

    Jerry Norris
  11. Jerry Norris

    Jerry Norris Guest

    Yes, Jim that is the intent of the project. Please allow me to

    I have a 20Hz sinewave from a function generator. It obviously has its
    own ground reference, ie. 0-2.5Vpp.

    I would like to convert this to two identical signals. One swinging 5V
    (or so) between the +3 and +9 battery potential. The other likewise
    swinging 5V, but between -3 and -9 batteries.

    IOW the two output signals are to appear soley between the two
    dissimilar plus battery terminals, and two dissimilar minus battery
    terminals respectively ... and not with any reference to an "offset"
    or common ground.

    I assume, to see it, the CRO probe would be placed across the 1K load
    resistor shown in my diagram.

    I realize this is not conventional practice, but the nature of my
    project is a physics experiment.

    Any way the above can be achieved, discrete or op amp, would be fine.

    Jerry Norris
  12. Jerry Norris

    Jerry Norris Guest

    I use Free Agent newsreader. It doesn't appear to support this
    function. I will check the binary group tomorrow. Maybe my server is

    Sorry for the trouble.

  13. Jerry Norris

    Jerry Norris Guest

    I would then need to build two dedicated signal generators, one that
    runs off +3 and +9, and the other from -3 and -9.

    For example two XR2206's, which will run on split supply.

    However, the output signals of the two emitter followers (npn and pnp
    versions), shown in my posted circuits, need to be identical, except
    for the differing potential.

    Maybe you have something in mind, but I don't see how this can be
    easily achieved without using one input signal for both.

    Jerry Norris
  14. Jerry Norris

    Jerry Norris Guest

    Thanks for the schematics. I will breadboard them today.

    Can they be separated into two circuits, one running off +9V and the
    other -9V, so I can have the option of applying an inverted signal to

    I can see the positively and negatively shifted waveforms on your
    sims, but where is the return for each?

    As previously indicated, I did not want ot reference back to the input
    signal ground. IOW the output returns, thorugh the load resistances,
    should be eually offset from the signal ground.

    For example, if the swing is 2.5 to 7.5V, the load return needs to be
    at 2.5V, not signal ground. Same for the other signal, but with minus
    signs added. Perhaps I am not reading the diagram correctly.

    BTW did you ever know Harry Lang on E Briown St? He introduced me to
    electronics when I lived in Phoenix years ago.

    Jerry Norris
  15. YD

    YD Guest

    Late at night, by candle light, (Jerry
    Norris) penned this immortal opus:
    You need just one generator, outputting 6vpp (+/- 3Vp). Split the
    signal, in one branch connect a 6V DC source between the signal and
    the output with + going to the output. For the other output just
    invert the source.

    +| 6V
    +--| |--------o -3 to -9 V
    | |
    | | 6V|+
    _ +--| |--------o +3 to +9 V
    / \ |
    | ~ |-3 to + 3 V
  16. Jerry Norris

    Jerry Norris Guest

  17. Jamie

    Jamie Guest

    I gotta say, this has been one of the longest threads based on the
    simple practice of a single transistor phase splitter circuit for which
    you feed the emitter side a (-) source instead of the common to generate
    your +&- outputs. One only needs to tailor the DC bias on the base to
    get the desired DC offset!

    Hell, you can even use a single supply source using a V-ground...
    20 v source into a Vground network ... :)

  18. Jamie

    Jamie Guest

    Not knowing everything that is needed for a proper design is a big issue
    how ever, if you were to look at this problem from a basic electrical
    point of view...!!!

    One common configurable control transformer found in basic electrical
    panels that allow various voltage configs. These xformers have 2
    windings on the output, (X1,X2 and X3,X4), which you use as separate
    outputs if you wish.. You config the input so that yields a 1:1 ratio in
    the transfer..

    Each secondary can be fed with a DC offset. One with + voltage and
    the other, - voltage.

    With that, the applied 20hz, which should pass fine on these
    transformers, will be seen with the desired offsets on the other side.

    If the signal is 180 unmatched, you simple flip one of the secondary
    outputs. Also this gives isolation with the input signal..

    Problem solved! Next? :)

  19. Jerry Norris

    Jerry Norris Guest

    I was hoping no one would notice. You must have given up on the human
    race learning from mistakes ;-)
    Hmm ... a fractionating transformer. Why didn't I think of that

    Thanks to all for their generous assistance.

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