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Hi Yair, There is no typical leakage for a schottky diode. It depends and the technology and a trade-off between forward voltage drop and leakage/reverse current. In general you can state that the logarithm of the reverse current is proportional the reverse voltage over some wider voltage range for a power rectifier. That would then correspond to a formula: Ir = Io*exp(c*Vr) with parameters Io and c depending on the power rectifier being used. At a higher voltage the leakage current will be higher and the dynamic resistance will be lower. Leakage current already starts to increase from relatively low reverse voltages and keeps on increase up to the rated voltage. You cannot assume leakage current will remain ‘low’ by taking a higher voltage rated part. The characteristics of a power rectifier are extremely dependent on temperature. At a higher temperature the leakage current will be much higher and the dynamic resistance will be much lower. Best Regards, Joris Lemahieu Application Engineer ON Semiconductor +32 55 33 29 49 From: Yair Darshan [mailto:YDarshan@xxxxxxxxxxxxx] Hi Joris, Few questions/
During 802.3af/at the 28uA came from the calculations shown in darshan_01_0518.pdf attached on page 18. It is based on a diode with minimum equivalent leakge resistor of 1Mohm. In real life, PDs that where using Schottky, pass the backfeed
test. If you look at the calculation, asymmetry of 10:1 between diodes where taken. Regards Yair From: Joris Lemahieu [mailto:Joris.Lemahieu@xxxxxxxxxx]
EXTERNAL EMAIL Hi all, I believe we are on the right track with the updates represented in the ‘yseboodt_01_0518_backfeed_baseline’. The only concern I still have is with a “3-Pair PSE” trying to detect a single-signature PD (just for a single port system). I have the impression the (schottky) diode reverse leakage has not always been taken into account properly: either just neglected or represented as being a resistor (without additional current source in parallel). See my presentation in attachment. My concern is that a PD with real (schottky) diode bridges might become non-compliant to the 3bt standard and that a “3-Pair PSE” would be allowed not being able to detect a PDs with real (schottky) diode bridges anymore, due to hard to meet leakage current requirements. As such I do not have any problem with that, but do we really want to go that far? Next to my presentation, I also attached a spice schematic file for those that would like make simulations. FYI, the name “3-Pair PSE” is short for
“a 4-pair capable PSE providing power in 2-pair mode, whereby two pairs are connected to the positive VPSE, and one pair is connected to
the negative VPSE“. Best Regards, Joris Lemahieu Application Engineer ON Semiconductor +32 55 33 29 49 To unsubscribe from the STDS-802-3-4PPOE list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-4PPOE&A=1 To unsubscribe from the STDS-802-3-4PPOE list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-4PPOE&A=1 |