Bipolar junction transistor have low power losses but have long switching time.(especially at turnoff).MOSFETs have very fast switching characteristics(low turn on and turn off times)but have higher power losses.IGBT combines the advantages of MOSFET and BJT.Thus an IGBT has low switching times as well as low power losses.Its called as IGBT or GEMET or COMFET(conductivity modulated field effect transistor). Configuration The configuration of an IGBT is shown in the figure below In many respects it is similar to a vertical diffused MOSFET(VDMOS).Main difference is the presence of p+ as injecting layer.Next is n+ layer(buffer layer).There is a p-n junction (j1) between these layers and two more junctions(j2 and j3).Thus this IGBT configurations has  a parasitic SCR.Turn  on  of this read more

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