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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] He calls it "a theoretical rectification formula giving the maximum rectification", with a footnote referencing a paper by Carl Wagner , Physikalische Zeitschrift 32 , pp ...
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 transfer function of an ideal diode has been given at the top of this (non-linear) section. However, this formula is rarely used in network analysis, a piecewise approximation being used instead. It can be seen that the diode current rapidly diminishes to -I o as the voltage falls. This current, for most purposes, is so small it can be ignored.
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.
The electrons and holes travel in opposite directions, but they also have opposite charges, so the overall current is in the same direction on both sides of the diode, as required. The Shockley diode equation models the forward-bias operational characteristics of a p–n junction outside the avalanche (reverse-biased conducting) region.
The Shockley ideal diode equation or the diode law (named after the bipolar junction transistor co-inventor William Bradford Shockley) models the exponential current–voltage (I–V) relationship of diodes in moderate forward or reverse bias. The article Shockley diode equation provides details.
Diode law current–voltage curve. For simplicity, diodes may sometimes be assumed to have no voltage drop or resistance when forward-biased and infinite resistance when reverse-biased. But real diodes are better approximated by the Shockley diode equation, which has an more complicated exponential current–voltage relationship called the ...
In low voltage converters (around 10 volts and less), the voltage drop of a diode (typically around 0.7 to 1 volt for a silicon diode at its rated current) has an adverse effect on efficiency. One classic solution replaces standard silicon diodes with Schottky diodes , which exhibit very low voltage drops (as low as 0.3 volts).