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Question about equivalent model

I have some doubts about equivalent model for pn junction...if i consider a pn junction, the large signal equivalent model is composed by a dc voltage (representing the cut-in voltage) and a resistor. If i use the pn junction above cut-in voltage, the space-charge-region vanishes, so it becomes a short circuit. But in a short circuit the voltage drop is ideally zero, so the voltage at anode and catode nodes are equivalent: if i consider equivalent model this is not true because there is the cut-in voltage)....what is wrong? thanks

Reply to
silusilusilu
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Because it's the large-signal model. More specifically, it's the large forward current model.

As you have wisely noted, you've stepped outside of the bounds where the model is valid. If you need to simulate or analyze circuit behavior that includes short circuits across the diode, you need to change to a more detailed model.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott

That's a terrible model. Google for a more realistic one.

There is no "cut-in voltage", and current is exponential on voltage, modified by a series resistance term that starts to matter at high currents.

John

Reply to
John Larkin

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