Voltage Regulator Experiment with a 12‑Volt Zener Diode

Parts and Materials

• Four 6‑V batteries (total 24 V when connected in series)
• 12‑V Zener diode (e.g., 1N4742, Radio Shack catalog #276‑563 or equivalent)
• 10 kΩ resistor

For this experiment, any low‑voltage Zener diode will work. We recommend a diode whose Zener voltage exceeds the voltage of a single battery so you can observe its behavior under sub‑breakdown conditions.

Cross‑References

Lessons In Electric Circuits, Volume 3, Chapter 3: “Diodes and Rectifiers”

Learning Objectives

• Understand how a Zener diode regulates voltage
• Recognize the role of a series resistor in a Zener circuit
• Analyze voltage drops across components at different supply levels

Schematic Diagram

Illustration

Instructions

Build the circuit shown above, ensuring the Zener diode is wired in reverse bias (cathode to positive, anode to negative). Use a single 6‑V battery as the power source and measure the voltage across the diode. Record this baseline reading.

Next, add a second 6‑V battery in series to create a 12‑V supply. Re‑measure the diode’s voltage drop and the resistor’s voltage drop with a multimeter.

Continue by adding a third and fourth battery, generating 18 V and 24 V supplies respectively. For each supply level, record the voltage across the Zener and the resistor. Observe that the Zener’s voltage never exceeds its breakdown value (≈12 V), while the resistor drops the excess voltage.

Key takeaways:

• The Zener diode clamps the voltage across itself to its rated value.
• It cannot create voltage; if the supply is below the Zener voltage, the diode’s drop equals the supply voltage.
• The series resistor limits current and absorbs the surplus voltage.

Computer Simulation

Schematic with SPICE node numbers:

Netlist (copy the following into a text file):

Zener diode v1 1 0 r1 1 2 10k d1 0 2 mod1 .model mod1 d bv=12 .dc v1 18 18 1 .print dc v(2,0) .end

A SPICE model uses a standard diode with the reverse‑breakdown parameter (bv=12) set to the desired Zener voltage.

Related Worksheets

• Zener Diodes Worksheet
• Regulated Power Sources Worksheet