Beginner : Basic Bjt inverter ,how

Discussion in 'The Projects Forum' started by bluestone, May 11, 2008.

  1. bluestone

    Thread Starter New Member

    May 11, 2008
    2
    0
    Hi to U all ,
    I'm new to electronics , and in practical stuff , so our dr asked me to make simple bjt (npn) Inverter ,
    This is the basic circuit
    I tried to fighure out the concept that i should do , i saw lots of website , but things get mixed up .
    i want to understand the main concept and the way i could detrmine the resistores RC , RB. if
    the voltage vin = 5 v
    vcc = 5 v
    and
    vin =1
    Transistor Bjt , (NPN 2n2222)
    [​IMG]
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    For example, if you use Rc=1K you will 5mA to drop 5 volts across it and thus invert you input (input=high, output=low). If the lowest value of the transistors gain is 30 for example, you will need a base current of Ic/30=5mA/30=0.167mA Thus if your input voltage is 5 volts, you will need a base resistor Rb=(5-0.6)/0.167mA=26 K , 0.6 is the voltage drop across the base-emitter diode of the transistor. A better design to ensure that the transistor will always be saturated we use a base current 10 times more than the calculated so the base resistor will be 2.6 K if you like and if the maximum base current allows us to do it (check the datasheet).
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Take a look at the material on BJT transistors in the AAC ebook at this link.

    hgmjr
     
  4. bluestone

    Thread Starter New Member

    May 11, 2008
    2
    0
    Thanks alot guys , im sorry for my late reponse though...
    I tried as you mentioned , and my calculation led to Vc = 0
    Thanks again.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    If you show us your calculation I'm certain we can determine where you have gone off track.

    hgmjr
     
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