Part of Made in India,Design Innovation

Workshop,2015

A  Fresh  New  Experience  in  Project-­‐Making  &  Learning!

PHYSICS INVESTIGATORY PROJECT ON

TRANSISTOR AS AMPLIFIER & SWITCH

Do  you  know  that  there  are  billions  of  transistors  used  in  the  produc6on  of  ICs  and  microprocessors?  Transistors  are  not  only  used  for  amplifica6on  in  sound  systems  but  their  ability  to  switch  between  the  two  states  (ON/OFF)  makes  them  the  nerve  cell  of  informa6on  technology.    In  this  project,  you  will  learn  about  the  characteris6cs  of  a  transistor  and  how  can  it  be  used  as  an  amplifier  and  a  switch.

In  this  project,  you  will  need  a  transistor,  two  resistors,  a  preset,  two  LEDs,  a  breadboard,  a  mul6meter  and  a  few  connec6ng  wires.  Varying  input  voltage  is  provided  to  the  base-­‐emiLer  junc6on  of  the  transistor  using  a  voltage  divider  circuit  made  using  a  preset.  The  cut-­‐off,  ac6ve  and  satura6on  regions  of  the  transistor  are  iden6fied  by  comparing  the  intensity  of  the  two  LEDs,  one  on  the  input  side  (base-­‐emiLer  junc6on)  and  the  other  on  the  output  side  (collector-­‐emiLer  junc6on).

 In  the  cut-­‐off  region,  both  the  LEDs  are  OFF.    In  ac6ve  region,  the  LED  connected  to  the  collector-­‐emiLer  side  glows  brighter  than  the  LED  connected  to  the  base-­‐emiLer  side  and  on  rota6ng  the  preset,  the  intensity  of  the  former  LED  increases  more  than  the  laLer.  

Now,  an  input  voltage  was  set  at  the  common  terminal  of  the  preset  and  it  was  measured  using  a  mul6meter.  The  base  and  the  collector  voltages  w.r.t  the  emiLer  were  measured  and  compared.  Similarly,  the  base  current  (Ib)  and  collector  current  (Ic)  were  measured  and  compared,  using  which  the  amplifica6on  factor  (hFE  =  Ic/Ib)  was  calculated.  The  experimental  value  of  hFE  lies  between  100  and  400  and  therefore,  it  verifies  that  the  transistor  is  in  ac6ve  region  and  acts  as  an  amplifier  with  the  base-­‐emiLer  junc6on  forward  biased  and  the  base-­‐collector  junc6on  reverse  biased.  

When  the  preset  was  rotated  to  its  extreme  leU,  both  the  LEDs  glow  brightly  and  the  transistor  reaches  its  satura6on  stage.  The  amplifica6on  factor  was  calculated  as  above.  The  hFE  obtained  was  less  than  100.  In  this  case,  the  transistor  acts  as  a  switch.  Again  the  base  and  the  collector  voltages  were  measured  and  compared  to  verify  the  condi6on  of  the  satura6on  state.  Both  the  base-­‐emiLer  and  base-­‐collector  junc6ons  are  forward  biased  in  the  satura6on  state.  The  value  of  the  satura6on  voltage  for  the  transistor  was  found  to  be  0.25-­‐0.6  V.

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You  may  also  refer  to  the  video:  TransistorsFor  more  projects  visit  our  website:  CoolJunk  

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