Diode V–I characteristics

Theory

A p–n diode does not give the straight-line V–I pattern of an ohmic resistor. In forward bias, its current rises steeply over part of the voltage range. In reverse bias below breakdown, a small leakage current usually remains. On a typical axial diode, a band identifies the cathode.

Treat 0.7 V for silicon as a useful approximation, not a fixed turn-on point. The curve changes with the device, current, and temperature. Record the voltage across the diode together with its current, then plot the readings with clearly labelled axes and units.

I ≈ Iₛ(e^(V/(nVₜ)) − 1)

Approximate junction relation below breakdown. Iₛ, n, and thermal voltage Vₜ reflect the device and its temperature.