Work out diode forward voltage drop instantly with clear inputs, formula shown and shareable results.
The Shockley equation gives forward voltage as n x VT x ln(I/Is), where the thermal voltage VT is kT/q — about 25.7 mV at room temperature. The logarithm is why forward voltage changes only about 60 mV per decade of current, and dynamic resistance is n VT / I.
Shockley diode equation
Vf = n x VT x ln(I / Is + 1), VT = kT/q
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
The saturation current grows very rapidly with temperature, and that effect outweighs the rise in VT, giving about -2 mV per degree.
Small-signal analysis. At 26 mV/I it is 0.26 ohm at 100 mA, which matters when a diode is used as a reference or a signal element.