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  1. #1
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    q1 fizics

    For the diode that conducts 2mA at a forward voltage drop of 0.3v and whose n=2. Find the equation of the straight line tangent at ID=2mA
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  2. #2
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    Quote Originally Posted by TAHIRI View Post
    For the diode that conducts 2mA at a forward voltage drop of 0.3v and whose n=2. Find the equation of the straight line tangent at ID=2mA
    <br />
I_D = I_S \left[ e^{\frac{V_D}{nV_T}}-1 \right]<br />

    Expand the RHS as a Taylor series about V_D=0.3:

    <br />
I_D = I_S \left[ \left(e^{\frac{0.3}{nV_T}}+(V_D-0.3)\left. \frac{d }{dV_D} e^{\frac{V_D} {nV_T}}\right|_{V_D=0.3}+ \cdots\right)-1\right]<br />

    Truncate the series after the first term to get:

    <br />
I_D = I_S \left[ \left(e^{\frac{0.3}{nV_T}}+(V_D-0.3)\left. \frac{d }{dV_D} e^{\frac{V_D} {nV_T}}\right|_{V_D=0.3}\right)-1\right]<br />

    When you simplify this using the given data you will find that the I_S can be eliminated but you will be left with V_T in the equation.

    RonL
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