Zener clamp and current budget

A diode that holds a voltage

A Zener diode is designed to conduct in reverse breakdown, where its voltage changes relatively little over a specified current range. A shunt regulator places it across the load; a series resistor limits the supply current, which splits between load and diode.

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EXPERIMENT BENCH

Change the circuit settings, predict the readings, then check a challenge. These are learning models, with the assumptions explained in each lesson.

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Why it works

Ideal fixed 5.1 V clamp, only while current is available. No breakdown-knee curve, tolerance, heating or failure; real parts have minimum current and power limits.

Vs is supply, R series resistance and RL load resistance. While clamped: Is = (Vs − 5.1)/R, IL = 5.1/RL and Iz = Is − IL. Is is supply current, IL load current and Iz Zener current; resistor power = Is²R. If the budget is insufficient, output falls below 5.1 V.

Difficulty

Build · Build it
Power on at 9 V, series resistor 330 Ω and load 1 kΩ. Read 5.1 V with positive Zener current.
Need a hint?
Vs = 9 V; R = 330 Ω; RL = 1 kΩ → 5.1 V; 6.718 mA
Explore · Change one thing
At supply 6 V and load 1 kΩ, hold 5.1 V with Zener current 2–10 mA.
Need a hint?
Vs = 6 V; R = 100 Ω; RL = 1 kΩ → 5.1 V; 3.9 mA
Solve it · Solve the challenge
At supply 12 V and load 500 Ω, hold 5.1 V with Zener current 5–15 mA and series-resistor power at most 0.2 W.
Need a hint?
Vs = 12 V; R = 330 Ω; RL = 500 Ω → 10.709 mA; 0.144 W

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