Zener Diode: 18 flashcards
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1. What is a Zener diode?
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A heavily doped p-n junction diode designed to operate reliably in the reverse breakdown region.
2. In which region does a Zener diode normally operate?
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Reverse breakdown region (Zener region).
3. What is the Zener breakdown mechanism?
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Direct rupture of covalent bonds by a strong electric field, creating electron-hole pairs. Occurs in heavily doped junctions with narrow depletion width.
4. What is the Avalanche breakdown mechanism?
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Carrier multiplication due to collision ionization. Occurs in lightly doped junctions with wider depletion region.
5. Which breakdown mechanism dominates for Zener voltages below about 5 V?
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Zener breakdown (high electric field).
6. Which breakdown mechanism dominates for Zener voltages above about 6 V?
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Avalanche breakdown (collision ionization).
7. What is the Zener voltage ($V_Z$)?
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The reverse breakdown voltage at which the Zener diode starts conducting heavily in reverse bias.
8. What is the Zener knee current ($I_{ZK}$)?
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The minimum reverse current required to keep the diode in the breakdown region for stable voltage regulation.
9. What is the Zener maximum current ($I_{ZM}$)?
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The maximum reverse current the diode can handle without damage due to power dissipation.
10. What is the Zener dynamic resistance ($r_z$)?
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The small-signal resistance in the breakdown region: $r_z = \frac{\Delta V_Z}{\Delta I_Z}$. Ideally zero for perfect regulation.
11. Draw the V-I characteristic of a Zener diode (describe key features).
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Forward bias: similar to normal diode. Reverse bias: small leakage until $V_Z$, then sharp increase in current with nearly constant voltage.
12. Why is a Zener diode heavily doped?
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To achieve a thin depletion region and low breakdown voltage (Zener effect), and to allow operation in breakdown without damage.
13. What is the main application of a Zener diode?
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Voltage regulation: maintaining a constant output voltage across a load despite variations in input voltage or load current.
14. How is a Zener diode used as a voltage regulator?
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Connected in reverse bias across the load, with a series resistor to limit current. The Zener maintains a constant voltage across the load.
15. What is the function of the series resistor in a Zener regulator?
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To limit the current through the Zener diode and drop the excess voltage, protecting the diode from excessive current.
16. What happens to the output voltage if the load current increases in a Zener regulator?
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The Zener current decreases to compensate, keeping the total current through the series resistor nearly constant, so output voltage remains stable.
17. What is the power dissipation formula for a Zener diode?
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$P_Z = V_Z \times I_Z$
18. What is a Zener diode's typical use in wave shaping?
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Clipping circuits: to limit or clip a waveform at a specific voltage level determined by $V_Z$.
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