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Shockley derives an equation for the voltage across a p-n junction in a long article published in 1949. [2] Later he gives a corresponding equation for current as a function of voltage under additional assumptions, which is the equation we call the Shockley ideal diode equation. [3]
The Shockley diode equation relates the diode current of a p-n junction diode to the diode voltage .This relationship is the diode I-V characteristic: = (), where is the saturation current or scale current of the diode (the magnitude of the current that flows for negative in excess of a few , typically 10 −12 A).
The characteristic curve (curved line), representing the current I through the diode for any given voltage across the diode V D, is an exponential curve. The load line (diagonal line), representing the relationship between current and voltage due to Kirchhoff's voltage law applied to the resistor and voltage source, is
It obeys Ohm's law; the current is proportional to the applied voltage over a wide range. Its resistance, equal to the reciprocal of the slope of the line, is constant. A curved I–V line represents a nonlinear resistance, such as a diode. In this type the resistance varies with the applied voltage or current.
This configuration is known as a constant-current diode, as it behaves much like a dual to the constant voltage diode (Zener diode) used in simple voltage sources. Due to the large variability in saturation current of JFETs, it is common to also include a source resistor (shown in the adjacent image) which allows the current to be tuned down to ...
A variety of silicon diodes of different current ratings. At left is a bridge rectifier. On the 3 center diodes, a painted band identifies the cathode terminal. Silicon diodes are the most widely used rectifiers for lower voltages and powers, and have largely replaced other rectifiers. Due to their substantially lower forward voltage (0.3V ...
Band diagram for p–n junction at equilibrium. The depletion region is shaded. φ B denotes band shift for holes and charges level. See P–n diode. The inner workings of a light emitting diode, showing circuit (top) and band diagram when a bias voltage is applied (bottom).
is the desired current of the LED in amps. The maximum continuous-on current is shown on LED datasheets, for example 20 mA (0.020 A) is common for most small LEDs. Many circuits operate LEDs at less than the specified maximum current to save power, or to reduce brightness, or to use a common resistor value. For indoor use, tiny surface mount ...