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I want to know about the forward voltage \$V_{f}\$ parameter of a diode device, given an I-V charateristic curve and in ambient temperature. What is the criteria to define the \$V_{f}\$ for any diode? How can I define it if I work with this current expression \$i_D = I_s (\exp^{v_D/V_{th}}-1)\$? Sometimes I see the value of this parameter like \$V_{f}=0.7\ \mbox{V}\$ for some type of diode, but how can I calculate given any \$i_D\$ expression?

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    \$\begingroup\$ Welcome to EE.SE. By Von I assume you mean the forward voltage drop. By criteria I assume you mean ambient temperature and forward current. Give us a few clues please. \$\endgroup\$ – Sparky256 Sep 23 '18 at 0:54
  • \$\begingroup\$ Hi @Sparky256 , thanks for your time, and sorry for my english. I edited the post. I mean about, given a I-V curve of the diode, how can I define the \$V_{on}\$? What is the criteria to build this parameter? \$\endgroup\$ – Alan Mejia Sep 23 '18 at 2:34
  • \$\begingroup\$ Read this answer: electronics.stackexchange.com/a/120612/27943 \$\endgroup\$ – nidhin Oct 19 '18 at 18:09
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If this is a small signal silicon diode, then use Vf=0.7V @ 1mA

But reducing the current by a log scale also reduces the forward voltage on a linear scale up to 5 decades down. Above this, the bulk resistance limits the minimum resistance and thus voltage rise with the current before its power limit.

For Power diodes, the internal bulk resistance limits the rise in voltage where they are rated for Vf at Idc(max).

For specific diode VI graphs, one needs a part number or datasheet below and above 1 mA. There are several non-ideal factors but common curves are available on the web.

For Engineering details

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