Re: some fun with "spice models" .... 1N4004 vs 1N4007

[Kevin Zheng]

The 1N4004 and 1N4007 are "general purpose" diodes that are now sold by 
several manufacturers.

The Vishay datasheet for this part compares the differences between the 
diodes in this family very nicely (table on page 1):

https://www.vishay.com/docs/88503/1n4001.pdf

The "only" difference appears to be the reverse breakdown ("maximum DC 
blocking voltage"), everything else appears to be the same!

I've reordered the SPICE model files so that you can see a side by side 
comparison:

     (400 V blocking)        (1000 V blocking)
  .model 1N4004 D        |  .model 1N4007 D
  + IS=5.31656e-08       |  + IS=1.09774E-008
  + N=2                  |  + N=1.78309
  + RS=0.0392384         |  + RS=0.0414388
  + EG=0.6               |  + EG=1.11
  + XTI=0.05             |  + XTI=3
  + BV=400               |  + BV=1100
  + IBV=5e-08            |  + IBV=0.1
  + CJO=1e-11            |  + CJO=2.8173E-011
  + VJ=0.7               |  + VJ=0.50772
  + M=0.5                |  + M=0.318974
  + FC=0.5               |  + FC=0.5
  + TT=1e-09             |  + TT=9.85376E-006
  + KF=0                 |  + KF=0
  + AF=1                 |  + AF=1

A parameter list for the diode model is here:

https://ngspice.sourceforge.io/docs/ngspice-html-manual/manual.xhtml#magicparlabel-6996

The reverse-bias breakdown voltage (BV) has changed from 400 to 1100. 
The saturation current (also "dark" current in reverse bias, IS) is also 
different. Differences in N (the denominator in the exponential 
relationship) also contribute to slight differences in forward current.

Avalanche breakdown in reverse bias happens when the applied electric 
field is so strong that the thermally generated carriers smack into 
stuff in the semiconductor, freeing more carriers that in turn smack 
into other stuff in the semiconductor, and so on (hence "avalanche" 
breakdown). When there are a lot of carriers, current is free to flow 
through the device, leading to excessive heat and eventual device 
failure if the current is not stopped.

The breakdown voltage of a PN junction is primarily a function of the 
doping concentrations on either side of the junction. Hence, all the 
parts in the family are probably more or less identical, except for the 
doping concentration on one side of the junction.

Anything to add, Al?

Regards,
Kevin