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Diode I–V characteristics and forward voltage calculator

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KEY POINTS

Diode current I = Is(exp(V/nVt) − 1) rises exponentially with voltage, increasing tenfold for about every 60 mV at room temperature with n = 1. That is why a silicon diode's forward voltage stays around 0.6 to 0.8 V even when current changes by orders of magnitude. Forward voltage falls by about 2 mV/°C as temperature rises, which is used in temperature sensors.

Inputs

Diode type (example SPICE parameters)Saturation current Is (27 °C) (A)Ideality factor nSeries resistance Rs (Ω)Barrier height or band gap Eg (eV)Temperature (°C)Forward current (mA)Reverse lookup: applied voltage (V)

Forward voltage Vf at 10 mA0.7332V

Temperature coefficient of Vf-1.54mV/°C

Differential resistance at the operating point rd5.557Ω

Saturation current Is at this temperature3.70×10⁻⁹A

Thermal voltage kT/q25.69mV

Current at 0.7 V5.4mA

Voltage per tenfold current increase (n·Vt·ln10)113.0mV/dec

Reverse breakdown and the transitions to recombination current at low current (n ≈ 2) and high-injection effects are not modeled. This simple model uses one n for the whole current range.

I–V characteristics (semi-log)

-40 °C25 °C125 °C

Forward voltage by current

Current	Vf (25 °C)	Vf (−40 °C)	Vf (125 °C)
0.001 mA	0.275 V	0.472 V	0.030 V
0.01 mA	0.388 V	0.560 V	0.126 V
0.1 mA	0.501 V	0.648 V	0.268 V
1 mA	0.614 V	0.737 V	0.418 V
10 mA	0.733 V	0.832 V	0.575 V
100 mA	0.905 V	0.978 V	0.784 V
1000 mA	1.603 V	1.652 V	1.520 V

Diode voltage follows the log of current

Current through a pn junction rises exponentially with forward voltage. At room temperature with ideality factor n = 1, current increases tenfold for every 60 mV or so. That is why the forward voltage of a silicon diode stays around 0.6 to 0.8 V even when current changes by orders of magnitude, and why the rule of thumb "a diode drops about 0.7 V" works.

Forward voltage falls by about 2 mV/°C as temperature rises. This is used in temperature sensors (on-chip thermal diodes), but it also causes thermal runaway in parallel diodes, where current crowds into the hottest device. Schottky barrier diodes have a low metal-semiconductor barrier, giving a forward voltage of 0.3 to 0.5 V, and no minority carrier storage, so they switch fast.

FAQ

Why is a diode drop about 0.7 V?

Current depends exponentially on voltage, so across the normal current range of a silicon diode the voltage changes only a little, staying around 0.6 to 0.8 V.

Why do Schottky diodes have lower forward voltage?

The metal-semiconductor barrier is lower than a pn junction's built-in barrier, giving 0.3 to 0.5 V, and there is no minority carrier storage, so they also switch fast.

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Last updated: October 23, 2026