diode equation

Discussion in 'Homework Help' started by God1600, Oct 13, 2008.

  1. God1600

    Thread Starter New Member

    Oct 13, 2008
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    0
    Hi All
    please help me out with the following problem.

    Temperature of the p-n junction is 300k,saturation current to be 5.0nA and emisssion coefficient to be 1,Calculate the ratio of the current through the diode for a 0.5v forward bias to the current for a 0.5v reverse bias.What is your comment on this ratio.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    I=Is*(e^(Vd/k*VT)-1)

    where
    I=diode through diode
    Is=reverse saturation current
    Vd=voltage across diode (actually across the junction)
    k=emission coefficient (constant which depends upon the construction of the diode)

    VT=thermal voltage =KT/q which at 300K approximately equals 25mV

    For Vd=0.5V

    I=(0.5*10^-9)*(e^(0.5/1*0.025)-1)=0.243A=243mA

    for Vd=-0.5

    I=(0.5*10^-9)*(e^(-0.5/1*0.025)-1)=-4.99*10^-10=-0.49nA
     
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