Timeline for What is a precise definiton of "cut-in" voltage as applied to diodes?
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| when toggle format | what | by | license | comment | |
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| Apr 25 at 17:26 | comment | added | 比尔盖子 | The "knee" on all exponential curves is an illusion - If you label your axis using a different order of magnitude, the knee shifts accordingly. The knee's location has no mathematical significance. But for practical purposes, the X axis is always in milliamps or amps, not in gigaamps, so the "knee" of a diode curve is around 0.7 V consistently. | |
| Apr 25 at 15:18 | history | edited | JRE | CC BY-SA 4.0 |
added 16 characters in body; edited title
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| Apr 25 at 15:13 | answer | added | Neil_UK | timeline score: 1 | |
| Apr 25 at 14:32 | comment | added | periblepsis | Regardless, the knee moves only tiny distances in terms of the voltage -- stepping only a small bit by \$\Delta V\$. Suppose \$\Delta V=100\:\text{mV}\$ (as in the 1N4148 diode case.) So if 10 mA matters to you but 1 mA matters less then perhaps the knee occurs at 630 mV. If 10 uA matters to you but 1 uA matters less, then the knee occurs at 330 mV. It works like that. But since the voltage only changes a little, it's common to see 330 mV as not so different from 630 mV. And to just say that the knee occurs somewhere around that region. | |
| Apr 25 at 14:21 | review | Close votes | |||
| Apr 27 at 22:05 | |||||
| Apr 25 at 14:09 | comment | added | periblepsis | The knee occurs where you decide things matter and where they don't matter. (With multiples of 10 piling up fast, there is most definitely a knee somewhere.) Of course, it's really still everywhere just the same self-similar exponential equation. | |
| Apr 25 at 14:07 | comment | added | periblepsis | Another way to look at this is that for every \$\Delta V\$ change in voltage there is a \$10\times\$ change in current. Step by \$\Delta V\$ and you go from 1 nA to 10 nA. And you don't care. Step again by \$\Delta V\$ and you go from 10 nA to 100 nA. And you don't care. Step again by \$\Delta V\$ and you go from 100 nA to 1 uA. And you don't care. Etc. But step by \$\Delta V\$ and you go from 10 uA to 100 uA. And now you start to care. Another \$\Delta V\$ and you are into milliamps. Etc. It doesn't take long before it really matters a lot. So going from 100 mA to 1 A really matters!! | |
| Apr 25 at 14:02 | comment | added | periblepsis | Exponential curves look linear when examined close enough. And everywhere. Meaning that if you look closely enough at 10 mA it looks linear and if you look closely enough at 1 nA it looks just as linear (but different slope.) The issue is that we generally don't care about 1 nA. But do care about 10 mA. So if you take a step back and look at many orders of magnitude, then there is a place where the change in current for changes in voltage we care about yield almost crazy changes in current. And before that point, almost negligible changes. That's the knee. | |
| S Apr 25 at 13:55 | review | First questions | |||
| Apr 25 at 14:16 | |||||
| S Apr 25 at 13:55 | history | asked | Qwe Boss | CC BY-SA 4.0 |