1.

The V to I characteristic of a silicon diode is shown in the figure. Calculate the resistance of the diode at (a) I_(D)=15mA and (b) V_(D)=-10V.

Answer»

Solution :Considering the diode characteristics as a straight line betweenI = 10 mA to I = 20 mA passing through the origin, we can calculate the resistance USING Ohm.s law.
(a) From the curve, at `I_(2)=20mA` for `V_(2)=0.8V, I_(1)=10mA` for `V_(1)=0.7V`
`therefore` Resistance of forward bias,
`r_(fb)=(DeltaV)/(DeltaI)`
`therefore r_(fb)=(V_(2)-V_(1))/(I_(2)-I_(1))`
`=(0.8-0.7)/((20-10)xx10^(-3))=(0.1XX10^(3))/(10)`
`therefore r_(fb)=10Omega`
(b) From the curve at `V=-10V, I=-1muA`
`therefore` Resistance of reverse bias,
`r_(rb)=(V)/(I)`
`therefore r_(rb)=(-10)/(-1xx10^(-6))`
`=1xx10^(7)Omega`


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