Calculating AC and DC Resistance of a Silicon Diode in 300K

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Discussion Overview

The discussion revolves around calculating the AC and DC resistance of a silicon diode at a temperature of 300K, using given parameters such as saturation current and forward current. The participants explore the differentiation of the diode current equation and seek assistance in determining the DC resistance.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant presents the equation for forward current in a diode and derives the AC resistance through differentiation, suggesting that the AC resistance is 1.3 ohms.
  • Another participant questions the correctness of the differentiation process used to find the AC resistance.
  • A participant confirms the differentiation is correct but initially confuses the results as pertaining to DC resistance.
  • There is a discussion on how to calculate the DC resistance, with one participant proposing that it can be found using the formula DC(resistance) = V(forward)/I(forward).
  • One participant expresses uncertainty about their calculated DC resistance value of 11.9 ohms and seeks verification from others.
  • Another participant agrees with the calculated value of approximately 11.97 ohms, indicating it aligns with the previous answer.

Areas of Agreement / Disagreement

Participants generally agree on the method for calculating AC resistance, but there is uncertainty regarding the DC resistance value and its calculation. The discussion remains unresolved regarding the accuracy of the calculated DC resistance.

Contextual Notes

Participants express uncertainty about the forward voltage, which is necessary for calculating DC resistance. There are also references to previous calculations and potential discrepancies with multiple-choice question answers.

Who May Find This Useful

Individuals interested in semiconductor physics, diode characteristics, and electrical engineering may find this discussion relevant.

rclakmal
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Diode ac and dc resistance?

here is my question ...saturation current of a silicon diode is 2uA.and forward current is 20mA...i want to find out the AC and DC resistances of the diode in 300k...

so i know that ,

I(forward)=I(saturate)[exp(eV/nKT)-1]

..so by differentiating both sides w.r.t to V i got that dI/dV=I(forward)*e/nkt...here KT/e=26mv so by subbing than (and also n=1 when conducting through diode)i got dV/dI=1.3ohms ...
so that is Ac resistance of the diode ...
but i don't know how to find the DC resistance of the diode can anyone help me out
 
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Are you sure that differentiation is right? doesn't look correct.
 


i think its correct ...what i have done is after differentiation i have subb i(forward) to the term I(saturation)*exp(ev/nKT)...and I am sure of that because i have done it before ...but i don't know how to calculate DC resistance ...DC(resistance)=V/I ...am i correct ...but i don't how to get a value for that ...
 


Yea sorry its correct. I thought doing that gave DC resistance not AC. Also do you know the foward voltage.
 


No i don't ,,,,,,,,,but after referring to some of my books i got some idea ...though i don't have the forward voltage i might be able to calculate it using forward and reverse currents by subbing them in the above equation then can get forward voltage ...

so i think DC(resistance)=V(forward)/I(forward)...
 


can someone check this answer for me ......here i forward is 20mA i saturated is 2uA and temp is 300k....i got the answer as R(dc)=11.9 ohms ...am i correct ?please someone check and tell me because in the MCQ question there is no such answer .....:(
 


I'll ask my teacher. That sounds a bit high though.
 


rclakmal said:
can someone check this answer for me ......here i forward is 20mA i saturated is 2uA and temp is 300k....i got the answer as R(dc)=11.9 ohms ...am i correct ?please someone check and tell me because in the MCQ question there is no such answer .....:(

I calculated 11.97 ohms which agrees well enough with your answer.
 


Thnaks dude !it was a great help!
 

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