Zener Characteristic, Power Rating, and Protection Resistor
For a Zener regulator in breakdown, the device voltage is approximately Vz, maximum safe current is Pmax/Vz, and the series resistance must be chosen from the worst-case source voltage and load current so Zener power remains within rating.
Why this shows up in the exam
Voltage-reference experiments · Selecting a protective series resistor · Determining a safe DC-source range
Learn the idea
A reverse-biased Zener regulates near its breakdown voltage only when current and power stay within safe limits. Once breakdown begins, extra supply voltage should fall across a series resistor rather than the Zener. The resistor limits current so the device can clamp voltage without exceeding its power rating.
🧠 Memory hook: Clamp the voltage, limit the current, check the power.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- I_Z,max = P_max/V_Z — maximum Zener current from its dissipation rating
- R_s >= (V_s,max - V_Z)/(I_Z,max + I_L) — protective-resistor bound for the stated load-current convention
- P_Z = V_Z I_Z — Zener dissipation check
How to approach it
- 1Read Vz and Pmax
- 2Compute the safe Zener-current limit
- 3Apply KVL at the worst case and verify power
Common slip-ups that cost marks
- •Connecting a Zener without a current-limiting resistor
- •Using Pmax as a current
- •Ignoring the worst-case source voltage or load branch
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
In a meter bridge, resistance 2 ohm is in the left gap and balance occurs at 40 cm from the left end. Find the right-gap resistance.
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