Question

The following table provides the set of values of $V$ and $I$ obtained for a given diode. Let the characteristics $\alpha$ be nearly linear, over this range, the forward and reverse bias resistance of the given diode respectively are

	$V$	$I$
Forward biasing	$2.0\, V$	$60\,mA$
	$2.4\,V$	$60\,mA$
Reverse biasing	$0\,.V$	$60\,mA$
	$-2\,V$	$60\,mA$

• A. $10 \,\Omega , 8 \times10^{6}\, \Omega$
• B. $20 \,\Omega , \times10^{5}\, \Omega$
• C. $20 \,\Omega , 8 \times10^{6}\, \Omega$
• D. $10 \,\Omega , 10\, \Omega$

Answer 1

Answer: (C)

For forward biasing,
$\Delta V = 2.4 - 2.0 = 0.4\, V$
$\Delta I = 80 - 60 = 20\, mA$
$\therefore r_{fb} = \frac{\Delta V}{\Delta I} $
$ = \frac{0.4}{20\times 10^{-3}} = 20 \Omega $
For reverse biasing,
$\Delta V = - 2 - 0 = -2\,V$
$\Delta I = - 0.25 - 0 = - 0.25\,\mu A$
$ r_{rb} = \frac{-2}{-0.25\times10^{-6}} $
$= 8\times 10^{6} \Omega$