Transistor = Beta 100

Discussion in 'General Electronics Chat' started by markidgmgig, Jan 18, 2008.

  1. markidgmgig

    Thread Starter Member

    Jan 18, 2008
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    I tried finding this in the data sheet but I can't identify what transistor having a beta of 100 is. Can anyone help me what code or what's it specific name so I can buy it.

    Thanks.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Can you point us to the datasheet for a specific device in question?

    hgmjr
     
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    It's usually "hfe" ...see attached for example.
     
  4. markidgmgig

    Thread Starter Member

    Jan 18, 2008
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    Uhmm... our instructor gave us an assignment in creating a multi stage amplifier circuit. I have all the materials already except for this Beta 100 transistor.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    Always a good clue is the fact that beta is a dimensionless quantity so if you look down the column labeled UNITS until you spot the one with no units indicated, that is often going to be beta.

    You can see what I am talking about by examining the datasheet in nomurphy's reply.


    hgmjr
     
  6. markidgmgig

    Thread Starter Member

    Jan 18, 2008
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    Sorry Im not very well in english.

    But looking from the picture is it the "PN2907A" the kind of transistor im looking for? Is that what you mean?
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    Both nomurphy's reply as well as mine are referencing the PNP datasheet in nomurphy's post.

    hgmjr
     
  8. markidgmgig

    Thread Starter Member

    Jan 18, 2008
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    Thanks. Ill try checking this in the store. So this should be the closest transistor with an equivalent value of 100 beta.
     
  9. techroomt

    Senior Member

    May 19, 2004
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    beta is a gain value not completely controllable by the transistor manufacturers. you may receive a "range" of beta values in the data sheet, but the actual beta will vary from transistor to transistor even with the same part number. for this reason transistor circuits were developed to eliminate the beta dependancy of the transistor, so that any transistor with that part number could be placed in the circuit and operate similarly. finding a transistor with a beta of a specific value requires buyilg several to many of a transistor type and testing the hfe as described. some multimeters have that function.
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    Are you sure you want PNP polarity?
     
  11. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    If you don't know the difference between an NPN and PNP transistor, and their applications, then you shouldn't proceed until you do ...or have more info from your professor on this project.

    There are many "complimentary" type transistors, I've attached the datasheets for a common pair, but you really should understand the design parameters.
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    Your instructor should have taught you that transistors have a range of beta. He should have shown how circuits can be designed to work well if a transistor's beta is from 50 up to 300.

    You cannot buy a transistor with a beta of 100. It might be 30, 100, 200 or 300.
    You must not be required to adjust something in a circuit to make it work with a certain amount of beta. the circuit must be able to adjust itself so that "any" transistor with the same part number (and many others) will work properly in a circuit.
     
  13. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Hey chaps, the poster could be struggling with a 'gain matched' circuit though that seems a bit thick for a beginner to have to do.

    mark

    The current gain, or beta or hfe varies with collector current and frequency of operation. Manufacturers' data sheets often supply curves to show this variation.

    It is possible your circuit reads 'beta greater than 100' rather than beta = 100. Some circuits, may require this.
     
  14. rwmoekoe

    Active Member

    Mar 1, 2007
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    i agree with techroomt.

    what your instructor meant was to find a transistor with beta at around (usually over, or at least) 100 times. unless it is for demonstration on this beta thing, any transistor would be better off having higher beta. the higher the better.

    the more important criteria you should meet are probably the max. power dissipation, max. c-e current, and max. c-e breakdown voltage.
    note that these criteria themselves have already naturally limited the beta. so you have only to check out wether the min. beta is met or not.
     
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