Question about βmax

  1. Hi!

    I'm tinkering with a circuit for an amplifier and have a question about entities. What's is the difference between β (hFE) and βmax?
     
  2. jcsd
  3. Even if you just have full bucket of transistors of the same type (2N2222). Each of them will have a slightly different beta. So the BJT vendors in data sheet tell as that in our bucket we will find transistors with beta value between Hfe_min and Hfe_max. But most of our transistors will have a typical value of beta also given in the datasheet.
    And when we design the amplifier circuit we always pick Hfe_min form datasheet.
     
  4. Ok... How would I interpret these different betas?
     
  5. phinds

    phinds 9,367
    Gold Member

    Do you understand what Beta IS? Min and max are just the highest and lowest expected values for a given type of transistor. If you don't know what the beta of a transistor is, then look it up.
     
  6. I don't understand your question?
    Transistor beta (Hfe) is not constant and datasheet for every transistor part number gives a range for Hfe, also every transistor has its own unique Hfe value. The Hfe is a range of numbers because they cannot make transistors accurately. Also the Hfe changes when the collector current is changed and the hfe changes when the temperature changes.
     
  7. Sry, I forgot to think before I posted the last one.
     
  8. is it true you can only use h-parameters for dc analysis? I know ebers-mole is their but I don't know calculus.
     
  9. dlgoff

    dlgoff 3,150
    Science Advisor
    Gold Member
    2014 Award

    Here is a good place to learn Transistor Operation without needing calculus; just a little algebra instead.

    also

    So you see, β gives you a ball-park current gain which can be helpful to obtain ball-part circuit design results.
     
  10. No, you cannot use a small signal h-parameters for DC analysis. You can use h-parameter only for small-signal analysis. For DC analysis all we need is to use both of Kirchhoff's law and Ohm's law.
     
  11. analogdesign

    analogdesign 798
    Science Advisor

    You should always only use ball-park values to design transistor circuits. Any design that depends on an accurate value of any specific transistor parameter is a bad design.
     
  12. dlgoff

    dlgoff 3,150
    Science Advisor
    Gold Member
    2014 Award

    :thumbs: That ain't no lie.
     
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