Resistor & diode in series

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madmartigano

Joined Oct 29, 2010
1
I'm asked to plot current vs. voltage for two circuits: one with just a constant voltage source and a forward-biased diode in series, the other with a constant voltage source, a forward-biased diode, and a resistor in series. All the information I have available for this question I've attached as a jpg. I'm basically having difficulty understanding how adding a resistor in series with a diode will affect the current of that circuit. I'm assuming it must somehow, I just don't know how to model it mathematically. My teacher apparently assumes this knowledge must be self-evident, but I still need someone to point out the obvious to me. Thanks in advance for any help.
 

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thatoneguy

Joined Feb 19, 2009
6,359
A resistor limits the current that can flow through a diode.

Roughly speaking, resistors change a voltage source into a current source.

This is the reason resistors need to be used with LEDs, they act like 20mA fuses with a ~2V drop.
 
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