Question

Two zener diodes ($A$ and $B$) having breakdown voltages of $6\text{V}$ and $4\text{V}$ respectively are connected as shown in the circuit below. The output voltage $V_0$ variation with input voltage linearly increasing with time, is given by:
($V_{input}=0\text{V}$ at $t=0$)
(figures are qualitative)

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

As input voltage varies between $0-4\text{V}$:
Zener Diodes does not reach breakdown condition. Hence $V_0=V_i$.

As input voltage varies between $4-6\text{V}$:
Zener diode with $4\text{V}$ will break down and $P.D.$ across this zener will become constant and remaining potential will drop across resistance in series with $4V$ zener diode.


As input voltage raises beyond $6\text{V}$:
Both zener diodes break down, output potential is ameasured across $6\text{V}$ diode, hence output potential remains $6\text{V}$

So, current graph between $V_0$ and $t$ will be