This simulator models a bipolar DC test source in series with a limiting resistor and a single silicon diode, solved as a true nonlinear Shockley-equation circuit rather than a fixed 0.7 V approximation. Sweep bias voltage, series resistance and junction temperature, reverse the physical package, or inject an open- or short-circuit fault, and watch the real operating point move on a live I–V curve and load line.
• A real-time 3D cutaway workbench with a bipolar DC source, series limiting resistor, axial glass diode package with cathode band, a magnified P-type region, N-type region and depletion/barrier region, and an I–V/load-line tracer — with home view, focus-selected-part, toggleable full enclosure, exploded view, auto-rotate, expand and show/hide-labels controls, tappable numbered components with callouts matching the companion diagram. • Five live controls: source voltage (−12 V to +12 V), series limiting resistor (100 Ω–5000 Ω), junction temperature setting (0–100 °C), a reverse-physical-diode-orientation checkbox, and a diode condition selector (healthy junction / open-circuit failure / short-circuit failure). • Play/pause, single-step (0.1 s) and larger-step (1 s) time controls, plus a playback-speed selector (10x slow motion, real time, 10x faster, 1 minute per second). • Reset laboratory and reverse-diode-orientation actions, with a live sequence narrative, operating-point summary and switch-state tokens. • Eight live metrics: applied source voltage, anode-to-cathode voltage, anode-to-cathode current, signed source current, series drop in the diode reference, diode dissipation, series resistor dissipation, and reverse leakage magnitude (nA). • A Curves & measurements tab with a dedicated forward I–V curve and load-line chart (healthy junction curve, resistor load line, live operating-point marker), plus circuit-measurement and response/stored-state charts, the full Shockley-equation model, and snapshot measurements. • An Experiments tab with four guided scenarios (forward operating point, reverse bias, warm junction, shorted diode), a model-verification bench of independent automated checks, and a timestamped event log with a copyable trial report. • A Learn & assess tab with guided lessons (identify anode/cathode, solve a nonlinear circuit, compare temperature and polarity, diagnose open/short failures), a knowledge-check quiz and a written scope/reference statement.
A real diode does not clamp at one fixed forward voltage — its current follows the Shockley diode equation, I = Is(T)[exp(Vd/(nkT)) − 1], with an ideality factor of 1.8 and a saturation current that itself depends on temperature. This simulator solves that equation together with Kirchhoff's voltage law for the source, series resistor and diode by bisection, so the displayed operating point is wherever the exponential diode curve actually intersects the resistor's load line — not an assumed 0.6–0.7 V constant.
Raising the junction temperature setting increases the modeled saturation current following an Arrhenius-style temperature dependence, which lowers the forward voltage needed for a given current. Reversing the physical package swaps which lead is anode and which is cathode, changing the sign convention the rest of the model uses without changing the underlying physics.
The I–V curve tab plots the diode's exponential forward curve in teal and the resistor's straight load line in amber; their intersection is the live operating point. An open-circuit fault drives current to zero regardless of applied bias, while a short-circuit fault forces the diode voltage to zero and lets the full source voltage divide across the series resistor alone — the experiments panel includes a worked shorted-diode case (5 V source, 1000 Ω resistor, 5 mA result) to check this directly.
The model is explicitly scoped: it is a generic small-signal silicon model (not a fitted 1N4148 datasheet fit), temperature is an imposed setting rather than a solved thermal balance, and reverse breakdown, reverse recovery, junction capacitance and high-injection effects are excluded, with the source limited to ±12 V. Component changes are treated as fresh design experiments at the retained state, not live component swaps on an energized circuit.
No. The simulator solves the full Shockley diode equation, I = Is(T)[exp(Vd/(nkT)) − 1], together with the series resistor and source using bisection, so the forward voltage that results depends on the actual current, temperature and device parameters rather than a fixed 0.7 V assumption. The 0.7 V figure is only a common rough approximation, and the Learn & assess quiz specifically checks understanding of this point.
Raising the junction temperature setting increases the modeled saturation current Is(T) through a temperature-scaling relationship anchored at 298.15 K, which lowers the forward voltage drop needed to sustain a given forward current. The Warm Junction experiment compares 75 °C against a 25 °C baseline at the same source and resistor to show this directly.
An open-circuit failure blocks current entirely regardless of applied bias, since no path exists across the junction. A short-circuit failure instead collapses the diode voltage to zero, so nearly the full source voltage appears across the series limiting resistor alone — the Shorted Diode experiment demonstrates a 5 V source through 1000 Ω producing exactly 5 mA once the diode presents zero resistance.
This is a generic small-signal silicon Shockley model, not a fitted 1N4148 or other datasheet-specific model, and temperature is an imposed input rather than something the circuit itself heats up to. Reverse breakdown, reverse recovery time, junction capacitance and high-injection effects are all outside scope, and the source voltage is limited to a ±12 V sweep.