and the
Shockley Equation.
My next project will be to design from scratch, a functioning and reliable high fidelity stereo headphone amplifier. Although based on a well established Class A-B model, in this project I will seek to derive all the related equations myself. But first there is a matter of investigating the 1N4148 diode (as one example), and its V-I characteristic.
There must be several such suitable diodes I could use to control the biasing of the eventual Class A-B push-pull headphone amplifier.
Below is a table showing forward bias I-V measurements I took, the input voltages varied from 0.575v to 0.835v.
I (mA)
|
0.393
|
0.644
|
1.060
|
1.747
|
2.680
|
4.160
|
6.340
|
9.520
|
13.900
|
19.540
|
26.485
|
30.614
|
V (volts)
|
0.575
|
0.600
|
0.625
|
0.650
|
0.675
|
0.700
|
0.725
|
0.750
|
0.775
|
0.800
|
0.825
|
0.835
|
Basic Diode Action
 |
| Under forward bias configuration (as shown) the width of the contact potential is narrowed as electron current is swept across the junction. |
William Shockley Equation
According to the Shockley Equation, the relationship between forward bias diode voltage and diode current for a PN junction diode is ...
Where
IO
= reverse saturation current, Io
= 25*10-9
for the IN4148
VT= KT/q ... thermal equivalant of voltage,
K = boltzmann constant, T = absolute temperature, q = electron charge.
And at 20C VT ~ 0.025v
VT= KT/q ... thermal equivalant of voltage,
K = boltzmann constant, T = absolute temperature, q = electron charge.
And at 20C VT ~ 0.025v
n= ideality factor,
n=1 for a perfect diode, but often n = 1.. 2.5
From my empirical results, I wanted to establish n, and by ignoring the '-1' term, and rearranging I obtain ...
For the 1N4148 data above, I calculated the mean value of n, that is ...
The correlation was remarkably good, better than I had anticipated!
n=1 for a perfect diode, but often n = 1.. 2.5
From my empirical results, I wanted to establish n, and by ignoring the '-1' term, and rearranging I obtain ...
For the 1N4148 data above, I calculated the mean value of n, that is ...
n = 2.351
(to 4 significant figures)
(to 4 significant figures)
With that I plotted the data vs the Shockley Equation model ....
The correlation was remarkably good, better than I had anticipated!
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