ElectronicsI_L2 - Real to Ideal We have seen what the p-n...

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Real to Ideal We have seen what the p-n junction does when biased. But it is very messy! At first, we will work with the ideal diode: – In forward bias, the ideal diode is a perfect conductor – In reverse bias, it is a perfect insulator – The terms forward and reverse bias indicate there is a polarity to the diode, which is distinguished by its conductive state We should keep in mind that some of those non-ideal characteristics come in very handy
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I-V of an Ideal Diode If a negative voltage, relative to the polarity of the diode, is applied, no current flows. The diode is said to be reverse biased. All voltages below zero on an I-V curve are taken to be reverse bias voltages If a positive voltage is applied, current will flow. The ideal diode, in fact will behave like a short circuit All voltage above zero on an I-V curve are taken to be forward bias voltages The ideal diode is thus a piecewise linear device – It’s response is composed of two linear regimes – Circuits that do not cross from one regime to the other can still be treated as linear – But if they do cross over, they can no longer be treated so simply Confused about Anode and cathode? The terms come from the original diodes which were vacuum tube devices
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An application • Even with this simplistic model, we can look at what is probably the most common application of a diode: rectification • A long time ago it was demonstrated that AC power is much more efficiently transferred over long distances, thus we have out 120V 60Hz • But most modern (and old!) systems need DC power. • How do we get DC from AC? – AC means that the polarity of the signal switches every half- period. This means that the time integral of the charge that would be moved to a system is zero! (AC can’t charge a battery) – If we stripped out one of these polarities, then we would have a net charge transferred – Diodes offer this possibility with their polarity dependent conductivity
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The Rectifier • Let’s take a closer look: • An AC signal is sent into a rectifier circuit, which consists of a diode, followed by a resistive load • When the signal’s polarity puts the diode in forward bias, the current can flow.
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This note was uploaded on 02/13/2012 for the course PHYSICS 16.365 taught by Professor Staff during the Summer '10 term at UMass Lowell.

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ElectronicsI_L2 - Real to Ideal We have seen what the p-n...

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