Zener Diodes & Regulation — A/L Physics

What must I remember about Zener Diodes & Regulation?

• Zener Diode Concept: Heavily doped p-n junction diode engineered specifically to operate reliably and continuously in the reverse breakdown region without being damaged.
• Breakdown Mechanisms: 1) Zener Breakdown (occurs at low voltages < 5 V in very narrow depletion layers where intense electric field directly tears covalent bonds to generate carrier pairs); 2) Avalanche Breakdown (occurs at higher voltages > 6 V where thermally generated carriers accelerate, collide, and ionize lattice atoms by impact avalanche ionization).
• Zener Voltage Regulation: In reverse breakdown, the terminal voltage remains virtually CONSTANT at the specified Zener voltage Vz across wide variations in load current and input supply voltage.
• Basic Zener Voltage Regulator Circuit: Unregulated DC input Vin connected through series current-limiting resistor Rs to parallel Zener diode and load resistor RL; Output voltage Vout = Vz (provided Vin > Vz).

Test yourself (1 minute)

1. Series Resistance Selection (Rs)

   Must satisfy Rs = (Vin - Vz) / (Iz + IL); Rs must be small enough to maintain minimum Zener knee current Iz_min at maximum load current IL_max, yet large enough that Zener power dissipation does not exceed maximum rated power Pz_max = Vz * Iz_max when load is disconnected (IL = 0).

2. Condition for Regulation

   Regulation is maintained strictly as long as Vin > Vz and Zener current Iz remains between Iz_min (knee current) and Iz_max (thermal limit).

3. Dynamic (Zener) Resistance rz

   rz = ΔVz / ΔIz; ideal Zener diode has rz = 0 (perfectly vertical I-V breakdown curve).

Practise Zener Diodes & Regulation questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 9: Electronics

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Where does Zener Diodes & Regulation fit in the syllabus?

Unit 9.3 · Year 2 · Term 2