Zener Diodes

1. Definition

1.1 Zener Diode

A Zener diode is a special type of diode designed to allow current to flow in the forward direction like a normal diode, but also in the reverse direction when the voltage exceeds its specified Zener breakdown voltage.
This makes it ideal for voltage regulation and reference applications.

zener diode example

Zener diode symbol

zener diode symbol

1.2 Zener Breakdown Voltage

The Zener breakdown voltage (Vz) is the reverse voltage at which the diode begins to conduct in reverse without damage.
Common values range from 2.4 V to over 200 V, depending on the diode design.

2. Features

  • Zener Voltage (Vz): the regulated voltage the diode maintains under reverse breakdown.
  • Power Rating (Pz): maximum power the diode can dissipate (Pz = Vz × Iz).
  • Reverse Current (Iz): current flowing during breakdown mode.
  • Forward Voltage Drop (Vf): ~0.7 V for silicon in forward bias.
  • Tolerance: how close the actual breakdown voltage is to the rated value.
  • Package Type: through-hole (DO-35, DO-41) or surface-mount (SOD-123, SOD-323).

4. How to Use

Safety Note

Operating a Zener diode above its power rating will cause overheating and possible failure.
Always use a current-limiting resistor in series when using it for voltage regulation.

4.1. Identify the Zener diode and polarity

  • Polarity: cathode marked with a band, anode is the opposite lead.
  • Markings often include the Zener voltage (e.g., “5V1” = 5.1 V).

zener diode marking

4.2. Choose the right Zener diode

  • Select Zener voltage based on the desired regulated voltage.
  • Ensure power rating is sufficient for the circuit.
  • Consider tolerance for precision applications.

4.3. Connect it correctly

  • Reverse bias for voltage regulation: cathode to positive, anode to ground.
  • Use a series resistor to limit current.
  • Can be placed in parallel with the load for shunt regulation.

4.4. Test and verify

  • Use a power supply and resistor to measure breakdown voltage.
  • Check that voltage across the Zener remains stable under varying load currents (within limits).

4.5. Install in circuit

  • On breadboard: insert leads into holes, observing polarity.
  • On PCB: solder into pads, matching the cathode band with the board marking.

5. When to Use

  • Voltage Regulation: maintain a stable voltage for sensitive circuits.
  • Overvoltage Protection: clamp excessive voltage to a safe level.
  • Voltage Reference: provide a fixed reference in measurement systems.
  • Waveform Clipping: limit signal peaks in audio and RF circuits.

6. Video Explanation

video coming soon