Question

$Ge$ and $Si$ diodes conduct at $0.3V$ and $0.7V$ respectively. In the following figure if $Ge$ diode connection is reversed, the value of $V_0$ changes by

• A. $0.2V$
• B. $0.4V$
• C. $0.6V$
• D. $0.8V$

Answer 1

Answer: (B)

Consider the case when $Ge$ and $Si$ diodes are connected as show in the given figure.
Equivalent voltage drop across the combination $Ge$ and $Si$ diode $=0.3V$
$\Rightarrow$ Current $i=\frac{12-0.3}{5k\Omega }=2.34mA$
$\therefore$ Output voltage $V0=Ri=5k\Omega 2.34mA=11.7V$
Now consider the case when diode connection are reversed. In this case voltage drop across the diode's combination $=0.7V$
$\Rightarrow$ Current $i=\frac{12-0.7}{5k\Omega }=2.26mA$
$\therefore V_0=iR=2.26mA\times 5k\Omega =11.3V$
Hence charge in the value of $V_0=11.7-11.3=0.4V$