On Thu, 2011-04-28 at 16:27 +0800, Adam Wang wrote: > Surely that zener has probably been ageing enough to have such high > 40mA reversed leakage current after my extremely high > consumption(66.8°C) on it. :-)
That zener is rated to 200°C so 66°C should not do any damage. On the other hand, because of the tolerances, the zener voltage can be as low as 4.85V for the 5.1V which might explain the current you have measured at 5V. > Use a bigger [email protected] is not a bad idea though to lower consumption > while 5.25V or 6V inputs. I repeat: 6V input is NOT SUPPORTED and we should NOT DO ANYTHING to make the device perform correctly at this voltage. However, we should not have any regression due to the protection circuit when operating in the supported voltage range (4.75V to 5.25V). The 5.1V zener does not meet this condition because it dissipates about 2W (probably heavily depending on process variations and temperature so this is heading for trouble) when operating at 5.25V, and 200mW on 5.0V. The 5.6V zener should solve this problem. > But don't forget that reviewing a 12V input result, there's 11 seconds > remaining there when even using 5.1V. Of course we don't know if > consumer usb device has over-protective parts on it even we insist on > a [email protected] Zener. Certainly, USB devices (as well as our PTH04000W regulator which is rated for 5.5V maximum) have a **LOT** more chance of surviving 5.6V for 11 seconds than they have of surviving 12V for an undetermined time. So the protection circuit would still be useful with a 5.6V zener. S. _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode Twitter: www.twitter.com/milkymistvj Ideas? http://milkymist.uservoice.com
