How to compute diode resistance ?

[boguslaw]

I'd like to ask if my thought are correct. Diode has a voltage drop across terminals so I assume it may be treated as a resistor (probably non-linear). Can I compute resistance of such diode from Ohm law taking voltage drop and current or there is another, simple way ?

[boguslaw]

ok.I found it in datasheet sorry for disturbing

[mikrovolt]

1. In a closed system:
A simple calculation may not be very accurate as V and I characteristics vary with different diodes at different conditions in a closed system. If you could get your diode to give similar results as figure 4 and 6 such as the following datasheet your electrical characteristics data should be permissable within an acceptable standard for peer review. You would be able to accurately state the forward voltage drop or Vf of your diode. Because the datasheet is concidered a standard for each manufacturer today fake parts were sold on ebay and forums get strange reports from oddball parts.

https://www.fairchildsemi.com/datasheets/1N/1N914.pdf

2. In an open system:
One example of diodes used in an open system comes up in the subject of crystal radio.
The author uses spread sheet and does not recommend Ohm's law be used. He is sorting material by what works.
See Crystal Galena and Pyrite Diodes picture discription.

kjs crystal radio, diode test

I use simulation software and build models and equivalent subcircuits from observation and experimentation.
In this way you get both datasheet and open systems approach by observation. It starts with basic model.
Having the ability to interchange models should lead to better improved models at least agree with the math.
Really the same approach but the style by hand by mathcad or simulation.
It is nice when the equivalent circuit works out to be simple often times it grows and adding linear equation or
simulataneous equations and the algebra is reduced to most simplified equation.

LTspice Tutorial: Part 4