Calculate the current flowing through a p-n junction diode using the Shockley diode equation.
Last updated: March 2026 | By ForgeCalc Engineering
The Shockley diode equation relates the current (I) flowing through a p-n junction diode to the voltage (V_d) applied across it. It is the fundamental mathematical model used to describe the non-linear, exponential behavior of semiconductor diodes.
The equation accounts for the saturation current (Iₛ), which is the small current that flows when the diode is reverse-biased, and the thermal voltage (V_T), which depends on the temperature of the semiconductor material.
Where:
• I is the diode current (A)
• Iₛ is the reverse saturation current (A)
• V_d is the voltage across the diode (V)
• n is the ideality factor (typically 1 to 2)
• V_T is the thermal voltage (kT/q ≈ 26mV at 300K)
The ideality factor accounts for non-ideal effects like carrier recombination in the depletion region. For silicon diodes, n is typically close to 1 for high currents and close to 2 for low currents.
Thermal voltage (V_T) is directly proportional to temperature. As temperature increases, the exponential curve shifts, meaning the diode will conduct more current for the same voltage.
Iₛ is the current that flows when the diode is reverse-biased. It is extremely small (typically picoamps or femtoamps) and is highly dependent on material properties and temperature.
Yes, the basic equation applies to LEDs, but they have much higher forward voltage drops (e.g., 2V to 3.5V) and different ideality factors compared to standard silicon signal diodes.
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