How to measure Hie of bootstrap circuit (common emitter)

Discussion in 'Homework Help' started by Watershadow, Jul 10, 2011.

  1. Watershadow

    Thread Starter New Member

    Jul 6, 2011
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    The text book I am using just assumes that the Hie is 2k. But says that its too complex to go into the detail for working out the Hie. Is there a specific way to work it out so that you would get roughly 2k specifically in a bootstrap setup for a common emitter.
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Show as the diagram
     
  3. Watershadow

    Thread Starter New Member

    Jul 6, 2011
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    Not really sure how, thats why I am asking.
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    What book you are using.
    And can you show as which type of the boostrap circuit you are talking.
    This type of the circuit

    [​IMG]

    In general case the Hie is BJT input resistance.
    and Hie is always equal to
    Hie = (β +1)*re = (β +1) * 26mV/Ic

    So what is your definition fro Hie ??
     
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  5. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Normally you would understand hie as a parameter used in a model for a transistor by itself :-

    hie= hfe*re, where re = 0.026/IC (approximately, at room temperature)

    You might therefore get a value of around 2kΩ with a typical transistor operating with collector currents of a few mA.

    If your text is applying h-parameters to describe the complete bootstrapped stage, that would be another matter. You would really have to supply more information to get a definite answer.
     
  6. Watershadow

    Thread Starter New Member

    Jul 6, 2011
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    The text book is called Analogue Electronics : Design principle by Nico J. Oosthuysen.

    Personally I think its a badly written book and I am studying in South Africa and the book is South African. It doesnt even show any information about Hie, I had to look online, but there is nothing about bootstrap and Hie. There are 2 resistors by the Emitter side with a capacitor connected across the one closest to the transistor. Will this make a difference to the formula considering there are now 2 "Re" resistors?
     
  7. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    The diagram looks like this?

    [​IMG]

    Or maybe this way

    [​IMG]

    But this circuit has nothing to do withe the bootstrap
     
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    Last edited: Jul 11, 2011
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