On Tue, 5 Jul 2016 16:00:05 -0400, you wrote: >On Mon, Jul 4, 2016 at 9:14 PM, 'Morgaine' via BeagleBoard ><[email protected]> wrote: >> John Syne writes: >>> >>> > a power supply that is spec’d at 4A should not shutdown when it sees a >>> > 4A load, but rather, it should current limit at 4A. If the power supply is >>> > spec’d at 4A, then 4A should not be treated as a short circuit. >> >> >> That's impossible. You can't recommend that fundamental electrical laws be >> overridden. :P >> >> If a PSU current limits at 4A, it can do so only by reducing its output >> voltage. This may then drop below specification for its load and this can >> have very bad consequences such as non-stop rebooting. There is no way for >> the voltage to be maintained above its minimum spec while still providing a >> current limit. > >Yes, but remember that the problem here is a startup inrush current, >which would be handled properly by current limiting. After all, that's >what the 2A current supply is doing: essentially, it soft-starts, >providing limited current charging the input caps, while ramping up >the voltage. Once the caps are charged and the supply voltage >stabilizes at the nominal value, the system progresses to boot.
Your discussion makes the assumption that the power supply provided or specified is current limited at the maximum output current. I (without looking at PS specs) have no such assurance. *with* such limiting, behavior is one way. Without that limiting, behavior is quite something else. I don't remember (particularly...) that the power supply specification mentioned current limiting. I thought that I had read only a voltage tolerance. People on this forum have mentioned using a particular supply (not model number, simply rating). The normal problem I have seen was the current supply rating, so that the BBB could boot as well as have sufficient power to drive such things as hard drives. It seems to me that this does not address the *maximum* current of the supply, nor does it specify what kind of supply is expected to supply that maximum. If this current capacity (as in surge current or current limiting) is a difficulty, then perhaps it needs to be addressed. I have not seen (nor particularly searched for....) such limitations. *if* they are important, then they need to be mentioned. If they are not, then perhaps that needs to be mentioned as well. Harvey -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/a3honbps1s8gtaspjnfhphdnfdo76n8cfv%404ax.com. For more options, visit https://groups.google.com/d/optout.
