Question 18.17: Fig. 18.43 shows a symmetrical zener shunt clipper with sine...
Fig. 18.43 shows a symmetrical zener shunt clipper with sine wave input. Determine the output waveform.
The symmetrical zener clipper uses two zener diodes that are connected as shown in Fig. 18.43. When the input is positive, D_1 \text { is forward biased and } D_2 is reverse biased (assuming that the value of V_{i n} is high enough to turn both diodes ON). When both diodes are conducting, the voltage from point A to ground will be equal to the sum of V_{Z 2} and the forward voltage drop of D_1 i.e., V_{F 1}=0.7 \,V.
∴ V_{\text {out }}=V_{Z 2}+V_{F 1}=V_{Z 2}+0.7 \,V
When the input is negative, D_1 is reverse biased and D_2 is forward biased. The output voltage in this case is
V_{\text {out }}=-V_{Z 1}-V_{F 2}=-\left(V_{Z 1}+0.7 \,V \right)
In practice, the two zeners have the same voltage rating i.e. V_{Z 1}=V_{Z 2}=V_Z.
∴ V_{\text {out }}= \pm\left(V_Z+0.7 \,V \right)