On 3/7/2010 8:16 PM, Bil Herd wrote: > Hi Jim > > One school of thought is that the expansion port is fused against shorts by virtue of the fuse in the main power supply. > I think the Cardco cart expander and FOTIOS' FXB-3 put a fuse on the expansion board as a way to make it easier to replace a fuse without opening the unit. > shorts, they don't do well at trying to just tell if your pulling too much current as they are too gross for that kind of discrimination. > I was considering the use of PTCs, not a regular fuse. > I also don't recommend a fuse on the regulated side of a supply, at that point you don't want any resistive components in series with the high current spike supply rails, you will drop voltage across the fuse element. > I am OK with that, but I have noticed that other designs put the fuse there. A PTC has a small resistance (.003 ohm) under normal load. > But otherwise if you wanted to figure a ballpark, take the power supply spec in A or W and subtract the measured amount that the main board is using. The expansion port budget that is what will be left. > I'm torn. Many of the designs include a fuse, though I agree it is unneeded. Jim Message was sent through the cbm-hackers mailing listReceived on 2010-03-08 04:00:04
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