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Lowering impedance.

  1. Jul 10, 2012 #1
    how could i lower the impedance affecting a certain material. im sure there is a circuit i can use to do this can any body help??
     
  2. jcsd
  3. Jul 10, 2012 #2
    I have no idea what you mean by lower the impedance affecting a certain material.
     
  4. Jul 10, 2012 #3

    berkeman

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    Staff: Mentor

    Oh come on, it's obvious. He means, uh, well I'm pretty sure he means.... Nope, you're right. Makes no sense at all yet :tongue2:
     
  5. Jul 10, 2012 #4
    Connect a negative impedance generator in series of course.
     
  6. Jul 11, 2012 #5
    A voltage follower is a 'circuit' that has a high input impedance and a low output impedance. Hope this is a constructive comment.
     
  7. Jul 11, 2012 #6
    ok im sorry guys i may not have made this verry clear. for instance crystals have a high impedance which causes low current can i either step this current up or do something to lower the impedance.
     
  8. Jul 11, 2012 #7
    Use a FET as source follower. Use an op-amp as voltage follower.
     
  9. Jul 11, 2012 #8

    berkeman

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    Staff: Mentor

    Sorry, but you are still not making sense (at least not to me). Why do you want to lower the apparent impedance of a crystal? The impedance of a crystal is high for a reason...
     
  10. Jul 11, 2012 #9
    im not saying i want to lower the impedance of crystal i was just using it as an example mate. i bassiclly have like high voltage and low current of a circuit and i need to some how gain more current. one way was lowering the impedance of like copper (for example) which should higher the current or i was thinking like a transformer.
     
  11. Jul 11, 2012 #10

    berkeman

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    Can you say more about the application? I'm worried that you are not getting good answers because we have no idea what you are asking about.
     
  12. Jul 11, 2012 #11
    without full information it is useful to make an educated guess and 'we' can go from there.
    It sounds to me (it did at the start) to be an impedance matching exercise.
    Now that a crystal has been mentioned I am even more certain that it is a high impedance that needs connecting/matching to a low impedance. I dont know what the particular application is but now there is something to go on.
    Voltage follower seems like a good start.
     
  13. Jul 11, 2012 #12
    ok guys there is no application other then a simulation im just playing around learning things, I bassiclly have multi-sim with an AC power source which is being converted into DC power using the full wave rectifier circuit but i want to be able to put a low AC current into the circuit and have a high DC current out of the circuit to get such a low current i have added a high impedance value but i was wondering if i could create a circuit to counteract this impedance or weather i could like use a transformer to step up current rather then voltage?
    ... has this made it any more clear.
     
  14. Jul 11, 2012 #13
    Good luck Daniel, glad to have been of help.
     
  15. Jul 11, 2012 #14
    thanks mate im just building the voltage follower on my multi-sim now.
     
  16. Jul 11, 2012 #15
    You lower the impedance with a transformer, but you lower the voltage output also. You are not gaining anything.

    If you have a high impedance output, you want to buffer it, use a voltage follower device. At that, this is a very general statement. You really have to have a solid idea of what kind of output signal, what output impedance it is, AND what do you want the output to be after the impedance transformation device. You are talking out of air right now and there is no one right answer here because nobody know what you are thinking.

    Just because a device has high output impedance don't mean it cannot drive. The collector of a BJT has output impedance in the north of 10MΩ easily. It can drive plenty. It might be a wrong thing to do to put a voltage follower in this case.

    Even if you are just doing simulation, you still need to know the condition and what do you want out of it, not just putting a voltage follower. I don't know Multi-sim, but someone here might know, attach your program so others can look at what you are trying to do. You learn a lot more by learning how to set the condition than just experiment on the device.
     
  17. Jul 11, 2012 #16
    What does "the collector of a BJT has output impedance in the north of 10MΩ easily" mean ???
     
  18. Jul 11, 2012 #17
    If you use BJT in common base stage, you can get as high output impedance of about 10MΩ. You can get a least a few mega ohms with a bipolar transistor. It is a current device.
     
  19. Jul 11, 2012 #18
    Only that you appear to be just fooling around with something you don't understand and are thereby wasting everybody's time.

    You should understand that an multisim AC power source will supply all the current required of it by the circuit attached. You have already noted that you have controlled this by adding a high impedance.

    In fact you have created a constant current source, for that is what one is. A perfect current source has a theoretically infinite imepedance.

    Having added a high impedance you are asking us how to counteract this?

    You say you want a low current in but a high current out and have been told that you can indeed do this with a transformer (although you have no need to) but you must reduce th voltage to do this.
    Not to reduce the voltage would be to contravene the law of conservation of energy since power = voltage times current.
     
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