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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 equation is called the Shockley ideal diode equation when the ideality factor equals 1, thus is sometimes omitted. The ideality factor typically varies from 1 to 2 (though can in some cases be higher), depending on the fabrication process and semiconductor material .
Its collector and base are tied together, so its collector-base voltage is zero. Consequently, the voltage drop across Q 1 is V BE, that is, this voltage is set by the diode law and Q 1 is said to be diode connected. (See also Ebers-Moll model.) It is important to have Q 1 in the circuit instead of a simple diode, because Q 1 sets V BE for ...
Various semiconductor diodes. Left: A four-diode bridge rectifier.Next to it is a 1N4148 signal diode.On the far right is a Zener diode.In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting.
Depending on the material and the degree of detail desired, a variety of energy levels will be plotted against position: E F or μ: Although it is not a band quantity, the Fermi level (total chemical potential of electrons) is a crucial level in the band diagram. The Fermi level is set by the device's electrodes.
A small-signal model is an AC equivalent circuit in which the nonlinear circuit elements are replaced by linear elements whose values are given by the first-order (linear) approximation of their characteristic curve near the bias point.
Besides impedance, Miller arrangement can modify the IV characteristic of an arbitrary element. The circuit of a diode log converter is an example of a non-linear virtually zeroed resistance where the logarithmic forward IV curve of a diode is transformed to a vertical straight line overlapping the axis. Not constant coefficient.
Zener diodes have a low breakdown voltage. A standard value for breakdown voltage is for instance 5.6 V. This means that the voltage at the cathode cannot be more than about 5.6 V higher than the voltage at the anode (though there is a slight rise with current), because the diode breaks down, and therefore conducts, if the voltage gets any higher.