[sdiy] Re: Bypass caps

[harrybissell]

LOL... of course the common term is "foldback current limiting" :^P

(confusin... ain't it ? :^)

but the jist of it is... to limit current you need to drop voltage. These things

latch, and don't try to self restart

H^) harry

James Patchell wrote:

> Power One Supply don't current limit...they fold back.  This is because
> those things are generally pretty beefy....A power supply with a standard
> current limit will eventually charge capacitors up.  On the LM723, it seems
> like I remember you can set it up to either current limit or fold back....I
> just checked the data sheet...and yes, you can make either a fold back or
> standard current limit regulator with it.
>
> The LM78xx regulators only have current limit.
>
> At 03:39 PM 12/6/2005 -0800, Harry Bissell Jr wrote:
> >No it does not. I'm using the standard "PowerOne" type supply...
> >if it gets an overcurrent, it shuts down the output and remains latched
> >off until power is reset.
> >
> >If you power off, then on again quickly, it will start because the caps
> >are not 'all the way' discharged and the current spike is less...
> >
> >that is still ugly...
> >
> >H^) harry
> >
> >Seb Francis <seb at burnit.co.uk> wrote:
> >>surely having a current limiting PSU (e.g. with an LM 723) would just
> >>bring the voltage up as the caps charged?
> >>
> >>seb
> >>
> >>
> >>Harry Bissell Jr wrote:
> >>
> >> > Just for the record (and noobs)
> >> >
> >> > another solution is to either
> >> >
> >> > Power one half the rack, then after a time delay
> >> > of a second or so... power the other half using a relay.
> >> >
> >> > ~or~
> >> >
> >> > Power the whole system through some series resistors that limit the
> >> > inrush current, then short across those resistors after a one second
> >> > delay.
> >> >
> >> > This is how I did my system... but the 'brute force' larger supply is
> >> > a valid option
> >> > too. Its more size and weight, less complexity.
> >> >
> >> > Engineering... ~make the choice~
> >> >
> >> > H^) harry
> >> >
> >> > */Tim Daugard /* wrote:
> >> >
> >> > From: "harrybissell"
> >> > .
> >> > >
> >> > What price failure ? More time is wasted by NOT using sufficient
> >> > bypass caps than is saved by not designing them in (in small
> >> > production runs). It is really hard to OVERDO the caps, unless the
> >> > power supply is unable to start because of the peak current :^P
> >> > >
> >> >
> >> > Which happens, my system reached the point where the power supply was
> >> > ad! equete for steady stae use, but couldn't power up the system. I had
> >> > to unplug one row of modules from the power chain until the system
> >> > powered up. When all the other modules had charge their caps, the last
> >> > chain got pluged in. I finally solved that problem by putting in an
> >> > upgraded power supply - two modules wide with 3X the current
> >> > capability.
> >> >
> >> > Tim Daugard
> >> > AG4GZ 30.4078N 86.6227W Alt: 12 feet above MSL
> >> > http://home.sprintmail.com/~daugard/synth.htm
> >> >
> >> >
> >> >
> >> >
>
>          -Jim
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>
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