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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits3 Marks
Question
A p-n junction germanium diode when forward biased has a drop of 0.3V which is assumed to be independent of current. The current in excess of 10mA through the diode produces a large Joule-heating which damages (burns) the diode. If we want to use a 1.5V battery to forward-bias the diode, what should be the value of resistor used in series with the diode, so that the maximum current does not exceed 6mA?
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Answer

The basic equation of diode-circuit is:
$\text{RI}+\text{V}_0=\text{V}_\text{B}$
$\Rightarrow\text{R}=\frac{\text{V}_\text{E}-\text{V}_0}{\text{I}}$
Here, $\text{V}-\text{B}=1.5\text{V},\text{V}_0$
$=0.3\text{V},\text{I}=5\text{mA}=6\times10^{-3}\text{A}$
$\therefore\text{R}=\frac{1.5-0.3}{6\times10^{-3}}$
$=\frac{1.2\times10^{3}}{6}$
$=0.2\times10^3\Omega$
$=200\Omega$

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