Diode knee voltage.

[Jimbz]

Hello everybody, small question:
What is a diode knee voltage ? And what is diode forward drop ?
As far as I figure, the knee voltage is the minimum voltage required for the diode to allow conducting the smallest bit of current ?
And forward voltage drop is the value to fully make the depletion zone disappear ?

[IanB]

How about this?

https://www.google.com/search?q=diode+knee+voltage&tbm=isch

[Dave]

As far as I figure, the knee voltage is the minimum voltage required for the diode to allow conducting the smallest bit of current ?

Nope. Diodes conduct anywhere above 0 volts (and below for that matter). It's just that the function of current with respect to voltage is exponential, so the current below the knee voltage will be very small.

[TimFox]

As the previous poster stated, diodes conduct at all voltages.  The I vs. V curve goes continuously through the origin (0,0) with a finite slope.
In the forward bias direction, the current increases exponentially (very fast) with voltage, so there is no well-defined "knee".
In the reverse bias direction, as the voltage goes negative the negative current saturates at a low "leakage" level, but increases abruptly at a well-defined knee voltage, becoming a Zener diode.
For on-purpose "Zener" diodes with knees greater than about 5 V, the diodes are actually "avalanche" diodes and the current increases much faster above the knee than with true Zener diodes at, say, 3.3 V knee.
By the way, if you are measuring current for a diode in a glass case (e.g., 1N4148), you may see current at zero voltage due to photocurrent induced by room lighting.