Question

the junction diode in the following circuit requires a minimum current 1 mA to be above the knee point (0.7 V ) of its I-V characteristics curve . the voltage across the diode is independent of current above the knee point . if $V_B=V$ then the maximum value of R so that the voltage is above the knee point, will be

• A. $4.3k\Omega$
• B. $860k\Omega$
• C. $4.3k\Omega$
• D. $860\Omega$

Answer 1

Answer: (A)

$4.3k\Omega$

At knee point across the diode is $0.7V$

Hence voltage across resistance $R$ is $5-0.7=4.3V$

$\Rightarrow$ using $V-iR\Rightarrow 4.3=1\times {10}^{-3}\times R\Rightarrow R=4.3k\Omega$