Diodeekvationen

Diodeekvationen, also known in English as the Shockley diode equation, describes the current through a p-n junction diode as a function of the voltage across the junction. It is a foundational model for the I–V characteristics of many diodes under forward bias and small reverse bias.

The current I as a function of the junction voltage V is given by I = I_s (exp(V / (n V_T)) − 1). In this expression, I_s is the reverse saturation current, V_T = k_B T / q is the thermal voltage, and n is the ideality factor, typically between 1 and 2. At room temperature, V_T is about 25–26 mV. The model predicts an exponential rise in forward current with voltage and a small, nearly constant reverse current of approximately −I_s for large reverse biases.

The diode equation assumes an ideal, smoothly varying pn junction with constant I_s and n. It does not account for series resistance, high-injection effects, or breakdown phenomena. In practice, I_s and n depend on temperature and device geometry; as temperature increases, I_s increases and V_T changes, shifting the I–V curve. At high currents, series resistance dominates and the simple form deviates, necessitating modified models that include a series resistance term or non-ideal effects such as those captured by Ebers–Moll approaches.

Applications of the diode equation include analysis of rectifiers, clippers, and other nonlinear circuit elements. It underpins many transistor and diode SPICE models, and provides a compact, physically grounded description of diode behavior.