Q.Explain the forward and the reverse characteristic of a Zener diode.

[!TLDR] Forward biased, a Zener behaves like an ordinary diode (conducts past a small knee voltage); reverse biased, it stays almost non-conducting until the Zener voltage $V_Z$, then breaks down sharply while the voltage across it stays pinned at $V_Z$. [!ANSWER] Forward: ordinary diode characteristic (small knee voltage, then rising …

The Zener diode's I-V characteristic (Fig. 16.7b) has two distinct regions. FORWARD characteristic: when forward biased, a Zener diode behaves exactly like an ordinary p-n junction diode -- negligible current flows until the forward voltage exceeds a small knee/barrier potential, past which the current rises steeply with further increase in forward voltage; nothing about this forward-bias behaviour distinguishes a Zener diode from any ordinary rectifier diode. REVERSE characteristic: when reverse biased, the diode initially carries only a very small, nearly constant reverse leakage current as the reverse voltage magnitude is increased -- essentially flat along the voltage axis. Once the reverse voltage reaches the diode's own ZENER VOLTAGE $V_Z$ (fixed by its doping level -- heavier doping giving a lower $V_Z$), a BREAKDOWN occurs: the reverse current increases suddenly and substantially, while the voltage across the diode remains essentially PINNED at $V_Z$, giving the characteristic's sharp, near-vertical drop at that fixed reverse-voltage value. This breakdown, unlike an ordinary diode's, does NOT damage the device (because of its heavy doping and correspondingly narrow depletion layer, which is what allows the controlled Zener-br …

Describe the forward branch (identical to an ordinary diode) and the reverse branch (small leakage current, then sharp constant-voltage breakdown at $V_Z$) of the Zener I-V curve separately, …

Describing the reverse breakdown as damaging the diode (true for an ORDINARY diode's uncontrolled breakdown) -- a Zener diode's whole design purpose is to survive and be usefully …