BZX84-C15 Forward And Reverse Bias Sweep

Application

This circuit shows the BZX84-C15 across both diode operating regions in one current-limited sweep. It is useful when choosing a Zener for clamp or reference behavior and when checking polarity before placing the part in a design.

Design Context

VBIAS is swept from -2 V to 24 V through RLIM. The BZX84-C15 anode is tied to the return node and its cathode is driven through the resistor. Negative bias forward-biases the junction, while positive bias reverse-biases the diode until it reaches the Zener region. RLIM limits current in both directions.

Expected Behavior

On the negative side of the sweep, Id flows in the forward direction and Vd stays near a normal silicon diode drop. As VBIAS becomes positive, current remains small until the cathode voltage approaches the 15 V breakdown region, then Id rises while Vd stays clamped near the Zener voltage.

Key Values

• VBIAS sweep: -2 V to 24 V in 0.1 V steps.
• RLIM: 1 kOhm current limiter.
• Vd: diode cathode voltage relative to the grounded anode.
• Id: diode branch current through the current probe.

Suggested Experiments

• Change RLIM to see how the resistor changes Zener current and clamp stiffness.
• Narrow the sweep around 14 V to 17 V to inspect the breakdown knee more closely.
• Compare the forward-bias region against the reverse-breakdown region to verify diode orientation.

Featured Component

The BZX84-C15 is the Zener diode under test. Its 15 V reverse-breakdown behavior makes it suitable for low-current voltage clamps, references, and overvoltage protection circuits when paired with an appropriate current-limiting impedance.