Topic: Analog Circuits
Determine the Voltage transfer characteristics of the following circuit comprising of Zener diodes having identical characteristics with Zener Breakdown voltage $V_z$ and Diode cut-in voltage $V_T$. (Circuit shows two Zener diodes connected back-to-back in series with a resistor R)
- A. Graph showing clipping at $(V_z+V_T)$ and $-(V_z+V_T)$
- B. Graph showing clipping at $(V_z-V_T)$ and $-(V_z-V_T)$
- C. Graph showing clipping at $V_z$ and $-V_z$
- D. Graph showing clipping at $(V_z-V_T)$ and $-(V_z-V_T)$ but asymmetrical
Answer: A. Graph showing clipping at $(V_z+V_T)$ and $-(V_z+V_T)$
Explanation: The circuit forms a double-clipper (or back-to-back Zener clipper). During the positive half cycle of the input, the top Zener diode is reverse biased and the bottom one is forward biased. The output voltage is capped when the top Zener reaches its breakdown voltage $V_z$ and the bottom one reaches its cut-in voltage $V_T$, clipping at $V_0 = V_z + V_T$. Due to the symmetry of the circuit, during the negative half cycle, the roles reverse, clipping at $V_0 = -(V_z + V_T)$.