Diode Equation Calculator - Calculator Academy

Calculate diode equation values for saturation current, diode voltage, ideality factor, temperature, or diode current from any 4 inputs.

Diode Equation Formula

The diode equation calculator uses the Shockley diode equation. Enter any 4 values, and the missing value is found by rearranging the same equation.

I_d = I_s\left(e^{\frac{qV}{nkT}} - 1\right)

I_s = \frac{I_d}{e^{\frac{qV}{nkT}} - 1}

V = \frac{nkT}{q}\ln\left(\frac{I_d}{I_s} + 1\right)

n = \frac{qV}{kT\ln\left(\frac{I_d}{I_s} + 1\right)}

T = \frac{qV}{nk\ln\left(\frac{I_d}{I_s} + 1\right)}

I_d = diode current, in amperes
I_s = saturation current, in amperes
V = voltage across the diode, in volts
n = ideality factor, unitless
T = absolute temperature, in kelvin
q = electron charge, 1.602176634 × 10^-19 C
k = Boltzmann constant, 1.380649 × 10^-23 J/K

The calculator converts the selected units into base units before solving. Current is handled in amperes, voltage in volts, and temperature in kelvin. If you enter Celsius or Fahrenheit, it is converted to kelvin for the equation.

Calculate diode current: uses I_s, V, n, and T in the Shockley equation.
Calculate saturation current: rearranges the equation to solve for I_s.
Calculate voltage: uses the natural logarithm form of the equation.
Calculate ideality factor: solves for n using the entered current, saturation current, voltage, and temperature.
Calculate temperature: solves for T in kelvin, then converts it back to your selected temperature unit.

Typical Diode Values and Unit Conversions

These values are common starting points. Actual diode behavior depends on the device type, temperature, material, and operating region.

Quantity	Typical Range	Notes
Ideality factor, n	1 to 2	n = 1 is closer to an ideal diffusion-dominated diode. n = 2 is common when recombination is significant.
Room temperature	293 K to 300 K	About 20 °C to 27 °C.
Silicon diode forward voltage	About 0.6 V to 0.8 V	Depends strongly on current and temperature.
Small-signal saturation current	Very small, often nA or below	The calculator accepts A, mA, and μA, so convert smaller values if needed.

Input Unit	Base Unit Used	Conversion
mA	A	1 mA = 0.001 A
μA	A	1 μA = 0.000001 A
mV	V	1 mV = 0.001 V
°C	K	K = °C + 273.15
°F	K	K = (°F – 32) × 5/9 + 273.15

Diode Equation Examples

Example 1: Calculate diode current

Suppose you enter:

I_s = 1 × 10^-12 A
V = 0.70 V
n = 2
T = 300 K

Using the diode equation:

I_d = 1\times10^{-12}\left(e^{\frac{(1.602176634\times10^{-19})(0.70)}{(2)(1.380649\times10^{-23})(300)}} - 1\right)

The result is approximately:

I_d ≈ 7.58 × 10^-7 A, or 0.758 μA.

Example 2: Calculate diode voltage

Suppose you enter:

I_d = 1 mA
I_s = 1 μA
n = 2
T = 300 K

Convert current units first: 1 mA = 0.001 A and 1 μA = 0.000001 A.

V = \frac{(2)(1.380649\times10^{-23})(300)}{1.602176634\times10^{-19}}\ln\left(\frac{0.001}{0.000001} + 1\right)

The result is approximately:

V ≈ 0.357 V, or 357 mV.

Diode Equation Calculator FAQ

Why does temperature need to be in kelvin?

The diode equation uses absolute temperature. Celsius and Fahrenheit are relative scales, so they cannot be used directly in the exponential term. If you select °C or °F, the calculator converts the value to kelvin before applying the formula.

What is the ideality factor?

The ideality factor, n, adjusts the equation for non-ideal diode behavior. A value near 1 usually represents a diode closer to ideal diffusion behavior. A value near 2 often represents stronger recombination effects. For many basic diode calculations, n is assumed to be between 1 and 2.

Does the diode equation include all real diode effects?

No. This equation is a useful model for diode current and voltage, but it does not include every practical effect. It does not directly account for series resistance, breakdown behavior, high-current effects, or the way saturation current changes with temperature unless you enter a new saturation current value for that temperature.