PHY066 · Electronics · Class 12 + College
Zener voltage regulation
Objective: To show that a Zener diode keeps the output voltage nearly constant when the input voltage changes.
🧰 Apparatus
- Zener diode (5.1 V)
- Series resistor (330 Ω)
- Load resistor (1 kΩ)
- Variable DC supply (0–20 V)
- Two voltmeters, milliammeter
📐 Formulas and SI units
I = (V_in − V_z) / R
I_Z = I − I_L; I_L = V_z / R_L
💡 Theory
A Zener diode is used in reverse bias. Once the reverse voltage reaches V_z it conducts just enough to hold its voltage at V_z, absorbing the extra current. The series resistor drops the rest: I = (V_in − V_z)/R. So the load sees a steady V_z.
🪜 Procedure
- Connect the series resistor, Zener (reverse) and load as shown.
- Increase V_in from 0 in steps.
- Record V_in, V_out and the currents.
- Plot V_out against V_in and find where it levels off.
- Change the load and check V_out stays steady.
📋 Observations Simulated values
✅ Result and conclusion
With 12 V in, 330 Ω and a 5.1 V Zener, 20.9 mA flows through R; the output stays at 5.1 V for any input above about 6.8 V.
🔬 In a real lab
The Zener voltage rises slightly with current and temperature; real output changes by a few tens of millivolts.
⚠️ Safety
Low-voltage DC only; check the Zener's power rating (I_Z × V_z) so it does not overheat.
❓ Quick check
1. A Zener regulator uses the diode in…
2. If V_in rises, the Zener current…
3. Purpose of the series resistor?
🏋️ Practice
EasyV_in = 9 V, V_z = 5 V, R = 200 Ω. I?
Answer: 20 mA
MediumPower in a 5.1 V Zener carrying 15 mA?
Answer: ≈ 77 mW
ChallengeName a use of a Zener regulator.
Answer: Steady supply for small circuits, reference voltages