@Victor

Noch mal ausführlicher. Bild  
Code:

                    VCC
                     +
                     |
                    .-.
                    | |
                  Rc| |
                    '-'
                     |
       Uc=Us+Ube+Ud  +--------->
                     |     A
       Ib=Ic/ß      ||     |Uc
                  Ie||     |
                    V|    ===
                     |    GND
                   A V D
                Ud | -
                   | |
                     |
                Ube> |
       |     Ib   /  |
      .-.  <---  / |<
    R2| |<---------|  T
      | |   A      |\
      '-'   |Us      |
       |    |       ||
      ===  ===    Ic||
      GND  GND      V|
                     |
                    ===
                    GND