Single Choice

Ge and Si diodes conduct at 0.3 V and 0.7 V respectively. In the following figure if Ge diode connection is reversed, the value of V$$_{0}$$ changes by

A0.2 V
B0.4 V
Correct Answer
C0.6 V
D0.8 V

Solution

Consider the case when $$Ge$$ and $$Si$$ diodes are connected as shown in the figure.
Equivalent voltage drop across the combination $$Ge$$ and $$Si$$ diode $$=0.3\ V$$

$$\Rightarrow $$ Current $$i=\dfrac {12-03}{ k\Omega} =2.34\ mA$$

$$\therefore$$ Out put voltage $$V_0=Ri=5\ k\Omega \times 2.34\ mA=11.7\ V$$

Now consider the case when diode connection are reversed. In this case voltage drop across the diodes combination $$=0.7\ V$$

$$\Rightarrow $$ Current $$i=\dfrac {12-0.7}{5\ k\Omega}=2.26\ mA$$

$$\Rightarrow V_0=iR=2.26\ mA\times 5\ k\Omega=11.3\ V$$

Hence charge in the value of $$V_0=11.7-11.3=0.4\ V$$

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