Which circuit condition is most likely to shift a diode's I–V characteristic curve so that the operating point (Q-point) moves to a different location?

Introduction / Context:
The operating point of a diode on its I–V curve depends on both the applied circuit conditions and the diode’s junction temperature. As power dissipation increases, the junction temperature rises, changing the curve and thus shifting the Q-point. Recognizing thermal effects is critical for stable, predictable operation.

Given Data / Assumptions:

• Diode obeys temperature-dependent I–V behavior (Shockley relation).
• Power dissipation P ≈ V_f * I increases junction temperature.
• Ambient and thermal resistance determine temperature rise.

Concept / Approach:
As temperature increases, the diode’s forward voltage for a given current typically decreases (approximately −2 mV/°C for silicon diodes around room temperature). Thus, heating shifts the forward I–V curve, moving the Q-point along the load line. Thermal feedback can amplify this shift unless managed by design.

Step-by-Step Explanation:
Increase load → higher current and power → junction temperature rises.Temperature rise reduces V_f at the same current.Lower V_f shifts the I–V characteristic, changing intersection with the circuit’s load line.The operating point moves accordingly, potentially increasing current further (thermal runaway risk in some devices).

Verification / Alternative check:
Datasheets show forward-voltage vs current curves at different temperatures; the curves translate with temperature, confirming Q-point shifts under heating.

Why Other Options Are Wrong:

• Higher resistance / lower voltage / lower current: These are external parameter changes that alter the load line, but the question asks for activity that shifts the device curve itself; heating (from higher power) directly moves the diode curve.

Common Pitfalls:

• Ignoring thermal effects in bias design; always consider heatsinking and derating.
• Confusing a load-line shift (external) with a device-characteristic shift (thermal).

Final Answer:
higher power (heat)