catflap.org Online Dictionary Query

  bipolar transistor
       
           A transistor made from a sandwich of n- and
          p-type semiconductor material: either npn or pnp.  The
          middle section is known as the "base" and the other two as the
          "collector" and "emitter".  When used as an amplifying
          element, the base to emitter junction is in a "forward-biased"
          (conducting) condition, and the base to collector junction is
          "reverse-biased" or non-conducting.  Small changes in the base
          to emitter current (the input signal) cause either holes
          (for pnp devices) or free electrons (for npn) to enter the
          base from the emitter.  The attracting voltage of the
          collector causes the majority of these charges to cross into
          and be collected by the collector, resulting in amplification.
       
          Contrast field effect transistor.
       
          (1995-10-04)
       
       

  bipolar transistor /baɪpˈəʊlə tɹanzˈɪstə/
  bipolarni tranzistor