Part of Made in India,Design Innovation

Workshop,2015

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PHYSICS INVESTIGATORY PROJECT ON

TRANSISTOR AS BLINKER(LED FLASHER)

Have  you  ever  seen  blinking  (flashing)  lights  on  highways,  mines,  tunnels  etc.?    Well,  you  can  actually  make  an  LED  flasher  circuit  on  your  own  in  less  than  an  hour.

To  make  an  LED  flasher  circuit  you  will  need  a  transistor,  a  resistor,  an  LED,  a  capacitor,  a  preset  and  a  few  connecDng  wires.  AFer  the  compleDon  of  the  circuit,  you  will  observe  that  on  rotaDng  the  preset  to  either  of  its  extreme  ends,  the  LED  starts  flashing.  You  will  also  observe  that  on  rotaDng  the  preset,  the  speed  of  the  flash  decreases  from  one  end  of  the  preset  to  the  other.  The  transistor  used  is  considered  to  be  a  combinaDon  of  two  diodes  i.e.,  the  base-­‐emiJer  juncDon  acts  as  the  first  diode  and  the  collector-­‐base  

juncDon  acts  as  the  second.  The  LED  flashes  because,  when  the  base  emiJer  juncDon  is  reverse  biased,  it  breaks  down  at  12V  and  starts  conducDng  in  the  reverse  direcDon.  As  a  result,  the  charged  capacitor  discharges  through  the  LED.  A  very  high  current  flows  through  the  LED  and  thus,  it  flashes.  

So,  the  B-­‐E  juncDon  of  the  transistor  acts  like  a  zener  diode.  This  effect  is  an  applicaDon  of  Esaki  effect  aka  tunneling  effect,  named  aFer  the  inventor,  Leo  Esaki.  He  was  a  Japanese  physicist  who  discovered  this  effect  while  working  at  Sony.  He  was  awarded  the  Noble  prize  in  physics  1973  for  his  discovery.  

Leo Esaki

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

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