Diode Equation

Source: YouTube

Ideal Diodes

The diode equation provides a way to calculate the current flowing through a diode based on the applied voltage. The Ideal Diode Law is expressed as:

$$I=I_{0}left(e^{frac{q V}{k T}}-1right)$$

where:

• I = net current through the diode
• I 0 = dark saturation current, the leakage current density of the diode in the absence of light
• V = applied voltage across the diode
• q = absolute value of electron charge
• k = Boltzmann’s constant
• T = absolute temperature in Kelvin

The dark saturation current (I 0) is a crucial parameter that distinguishes one diode from another, reflecting the recombination in the device. A diode with higher recombination will have a larger I 0. It is important to note that I 0 increases with temperature and decreases with improved material quality.

Non-Ideal Diodes

For real diodes, the expression is modified to include an ideality factor (n), resulting in:

$$I=I_{0}left(e^{frac{q V}{n k T}}-1right)$$

Where n is an ideality factor between 1 and 2, typically increasing as the current decreases. The behavior of non-ideal diodes can be visualized through the diode equation plotted on a graph, where changes in saturation current and ideality factor affect the IV curve. It is important to understand that in real devices, the saturation current is strongly influenced by temperature, and variations in the ideality factor also impact the saturation current.

The diode law is exemplified for silicon, showcasing that increasing temperature causes the diode to “turn ON” at lower voltages.

Source: All About Circuits

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