How Is Resistance Calculated in Different Bias Regions of a Diode?

AI Thread Summary
Resistance in different bias regions of a diode can be calculated using the formulas R1 = V1/I1 and Rp = (V2-V1)/(I2-I1), which leads to the parallel resistance R2 calculation. The user provided specific values for voltage and current to derive R1 as approximately 1785.71 ohms and Rp as 100 ohms. The calculation for R2 resulted in a negative value of about -105.93 ohms, indicating an error or an unusual scenario in the circuit analysis. Additionally, there was a request for clarification on the question format instead of links, highlighting the need for accessible information. The discussion emphasizes the importance of correct calculations and clear communication in solving diode resistance problems.
eximius
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Note: This is a past paper, I'm simply revising for an exam. But I thought that this was the best forum to stick it in.

Homework Statement



http://exampapers.cf.ac.uk/papers/engin/en1051/en1051a09.pdf

Section A, Q1 c

[PLAIN]http://img684.imageshack.us/img684/9695/questionm.jpg

Homework Equations



R1 = V1/I1
Rp = (V2-V1)/(I2-I1) = R1||R2
R2 = RpR1/(Rp-R1)

The Attempt at a Solution



R1 = 0.5/280x10-6 = 1785.71 ohms
Rp = (0.54 - 0.5) / (680x10-6 - 250x10-6) = 0.04 / 4x10-4 = 100ohms = R1||R2
R2 = RpR1/(Rp-R1) = 178571 / (-1685.71) = -105.9322185 = -105.93 ohms
V1 = 0.5V

Diagram -

[PLAIN]http://img407.imageshack.us/img407/4486/diagrame.jpg

Forgive the wrong symbols, difficult with paint.
 
Last edited by a moderator:
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That link:

A username and password are being requested by https://exampapers.cf.ac.uk . The site says: "Enter your Cardiff University username & password"

Can you post the question rather than link to it please.
 
Last edited by a moderator:
Zryn said:
That link:



Can you post the question rather than link to it please.

Sorry I've fixed it.
 
Bump, sorry.
 

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