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# B3 - Section B3 The Practical Diode OK the ideal diode is...

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Section B3: The Practical Diode OK, the ideal diode is an extraordinarily well-behaved creature that allows us to deal with its nonlinearities in unbelievably reasonable terms. But...and there’s always a but... we have to look at the deviations from ideal that materials, fabrication and miscellaneous stuff introduces. We’re going to approach this by removing some of the ideal approximations to define a semi-ideal case. Then, as promised by the title of this section, practical considerations will be introduced and we’ll end up with a pretty realistic device. To begin, recall from our discussion of diffusion that the free electrons in the n-type material and the free holes in the p-type material will move across the junction until equilibrium is reached. The width of the resulting depletion region is related to the barrier potential and is a function of applied bias . I realize that all these terms are somewhat overwhelming, but if they are not comfortable, please review The pn Junction discussion. These concepts are fundamental to the design, operation and manipulation of all semiconductor devices and the sooner they are internalized, the less “painful” future material will be! Now , with that said, let’s look at how a diode actually works... The diode current equation presented in Equation 3.26 defines an exponential relationship between the diode current (the dependent variable) and the diode voltage (the independent variable) and is derived from the physics of Section A. This equation holds over at least seven orders of magnitude of current and is truly valuable in defining the behaviors of semiconductor diodes (and later bipolar junction transistors). NOTE: Please refer to notation conventions for a description as to significance of upper and lower case characters. ) 1 ( = T D nV v O D e I i (Equation 3.26) where: i D is the current through the diode v D is the voltage (potential difference) measured across the diode terminals I O is the reverse saturation current

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n is a device constant between 0.5 and 2 that is dependent on material, diode construction, and operational considerations.
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B3 - Section B3 The Practical Diode OK the ideal diode is...

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