Biasing a transistor

Discussion in 'General Electronics Chat' started by i_nour, Oct 1, 2016.

  1. i_nour

    Thread Starter New Member

    Nov 9, 2015
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    Why do we -usually- have to use a DC voltage (power supply) to bias the transistor?
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Because the difference is bias point is what we're more interested in. If bias point was unstable, results would be invalid.
     
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  3. upand_at_them

    Active Member

    May 15, 2010
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    It's more fun that way.
     
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  4. crutschow

    Expert

    Mar 14, 2008
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    You can't use AC to bias a transistor, so DC is all that's left. :rolleyes:
     
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  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Usually you say? You are wasting everybody's time.
     
  6. hp1729

    Well-Known Member

    Nov 23, 2015
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    (100 words or less ...)

    The objective of setting a bias point in a transistor circuit is to put the transistor into conduction but not saturation. An input AC signal increases or decreases the conduction to produce a full waveform out.

    Setting this bias point determines the class of the amplifier. What input voltage will produce what kind of output.
     
  7. ci139

    Member

    Jul 11, 2016
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    how about Ge ones? or the attachment? -ss
     
    Last edited: Oct 8, 2016
  8. MrChips

    Moderator

    Oct 2, 2009
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    Imagine I have a 4-metre high wall to paint.

    I can only reach the lower 2 metres while standing on the ground.
    Hence I have to bias my height upwards by standing on a 2-metre step ladder.
    Now I can paint from the centre of the wall and cover the whole height.

    Hope this helps.
     
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  9. BR-549

    Well-Known Member

    Sep 22, 2013
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    Because a transistor is a one way DC device. It's a pilot check valve. We can keep the check valve open a little bit (if we want to) with DC bias.
     
  10. merts

    New Member

    Apr 1, 2016
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    If you look at the specs.for a transistor it starts at zero and goes into saturation.
    Normally biasing is used to allow it to operate in a linear manner for regular use.
    However you can bias it to operate anywhere along the graph.Since it is a non linear device
    square,log,cube and all sorts of outputs can be achieved.Therefore you bias it to get an output
    that is suited for the project being design.
     
  11. hp1729

    Well-Known Member

    Nov 23, 2015
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    Why do you think they would be different?
    Re: attachments
    Enough base current to turn them on.
     
  12. hp1729

    Well-Known Member

    Nov 23, 2015
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    Good, and in 100 words or less.
     
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  13. ci139

    Member

    Jul 11, 2016
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    as amazing as it may sound i don't think - i watch and stay baffled about what the spice is showing

    however the tunnel diodes have negative impedance - those things are quantum mechanics devices - i won't go predicting what is or is not possible here - if you tell me how to measure the circuits without signifficantly affecting (pushing) their operation - id likely made it clear
     
    Last edited: Oct 8, 2016
  14. hp1729

    Well-Known Member

    Nov 23, 2015
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    Isn't everything a quantum mechanics device? :)
     
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