4 ms·
The description of forward current and the graph are completely wrong. The graph shows approximately linear current above 600 mV, and the text says "When the th
by kens 11mo ago
The description of forward current and the graph are completely wrong. The graph shows approximately linear current above 600 mV, and the text says "When the threshold is cleared, the diode admits current that’s roughly proportional to the “excess” applied voltage, an ohmic behavior that’s a consequence of the resistance of the material itself".
The current through a diode is exponential with voltage, not "proportional". The graph shows 1.6V applied to a diode yielding 250 mA. In reality, this isn't possible since you'd get a huge current and destroy the diode.
See the Shockley diode equation: https://en.wikipedia.org/wiki/Shockley_diode_equation https://en.wikipedia.org/wiki/Shockley_diode_equation
I'm surprised that nobody has mentioned that the article is messed up, so am I missing something here?
- manwe150 11mo agoThe Wikipedia equation there mentions the formula ignores the contribution of the internal resistance, which would make it proportional. It seems the article assumes that resistance is a significant contribution (possibly even just from their voltage source) while you assume it is not, for any given particular diode being evaluated or measured, either could be right
- bombela 11mo agoWikipedia says: > Internal resistance causes "leveling off" of a real diode's I–V curve at high forward bias. The Shockley equation doesn't model this, but adding a resistance in series will. For small diodes and all LEDs as far as I know, it will level alright. Leaving behind a cute little smoldering crater where the now vaporized diode used to be. https://www.onsemi.com/download/data-sheet/pdf/1n4001-d.pdf https://www.onsemi.com/download/data-sheet/pdf/1n4001-d.pdf Take this very generic diode here. When mounted as instructed for the highest heat dissipation, it should gain 50°C per Watt. The flattening of the Current-Voltage curves starts at around 1A. As the diode heats up, the resistance lowers. Extending the limits. Maximum before damage is 150°C. Minus 25°C ambient leaves us 125°C. Divided by 50°C/W gives us 2.5W. Around 2.8A-3A at 0.8V-0.9V forward voltage. But the curve is barely proportional at 5A. You might also notice that the datasheet doesn't provide numbers beyond that point. Presumably because the diode left the room then.
- SAI_Peregrinus 11mo agoIn practical diodes it's much more likely to be a minimal contribution.