Diode modelling

In electronics, diode modelling refers to the mathematical models used to approximate the actual behaviour of real diodes to enable calculations and circuit analysis. A diode's I-V curve is nonlinear (it is well described by the Shockley diode law). This nonlinearity complicates calculations in circuits involving diodes so simpler models are often required.

This article discusses the modelling of p-n junction diodes, but the techniques may be generalized to other solid state diodes.

The Shockley diode equation relates the diode current ${\displaystyle I}$ of a p-n junction diode to the diode voltage ${\displaystyle V_{D}}$. This relationship is the diode I-V characteristic:

where ${\displaystyle I_{S}}$ is the saturation current or scale current of the diode (the magnitude of the current that flows for negative ${\displaystyle V_{D}}$ in excess of a few ${\displaystyle V_{T}}$, typically 10⁻¹² A). The scale current is proportional to the cross-sectional area of the diode. Continuing with the symbols: ${\displaystyle V_{T}}$ is the thermal voltage (${\displaystyle kT/q}$, about 26 mV at normal temperatures), and ${\displaystyle n}$ is known as the diode ideality factor (for silicon diodes ${\displaystyle n}$ is approximately 1 to 2).

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