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Interactive Lab

Zener Diode

Explore the IV characteristic of a Zener diode — forward bias with exponential turn-on, near-zero reverse current, and sharp Zener breakdown. Switch to regulator mode to see how Zener diodes maintain constant output voltage despite varying input.

Diode State

Voltage0.00 V
Current0.00 mA
RegionOff
Power0.00 mW

Parameters

VZ5.1 V
VT25.9 mV
Temperature300 K
n (ideality)1.5

Regions

Forward Bias
Reverse Bias
Breakdown
Operating Point
Drag the Applied Voltage slider from −10V to +2V and watch the operating point move along the IV curve. At the Zener breakdown voltage, current surges in reverse. Switch to Regulator Circuit mode to see voltage regulation in action with animated charge carriers.

Understanding the Zener Diode

A Zener diode is a specially designed diode that can conduct in reverse at a precise breakdown voltage. Unlike regular diodes that are damaged by reverse breakdown, Zener diodes are engineered to operate reliably in this region, making them essential components in voltage regulation circuits.

Shockley Diode Equation

I = I₀(e^(V/nV_T) − 1) — This equation describes the forward-bias exponential relationship between current and voltage. I₀ is the reverse saturation current (~1nA), n is the ideality factor (1–2), and V_T = kT/q is the thermal voltage (~26mV at room temperature).

Three Operating Regions

Forward bias: Above ~0.6V, current rises exponentially. Reverse bias: Between 0V and −V_Z, only tiny leakage current flows. Zener breakdown: At V = −V_Z, the electric field across the depletion region becomes strong enough to pull electrons from their bonds (Zener effect) or accelerate carriers into avalanche multiplication.

Voltage Regulation

In a voltage regulator circuit, a Zener diode connected in reverse bias across the load maintains nearly constant output voltage. As input voltage varies, the Zener absorbs the excess, keeping the load voltage at V_Z. This works because the Zener’s near-vertical IV curve in breakdown means large current changes for tiny voltage changes.