Re: Cheap/generic PSUs - any good? (was: Low power socket A)

From: Tony (tony_roe_at_tpg.com.au)
Date: 10/03/04 

Date: Mon, 04 Oct 2004 07:41:52 +1000

On Sun, 03 Oct 2004 14:20:22 -0500, David Maynard <dNOTmayn@ev1.net>
wrote:

>Mike wrote:
>
>> In article <10lej1o8vmhp834@corp.supernews.com>,
>> David Maynard <dNOTmayn@ev1.net> wrote:
>>
>>
>>>>Died taking out numerous components. Returned for replacement.
>>>
>>>No offense but your analysis of what caused the failure is, shall we say, a
>>>bit abbreviated. One thing that sticks out is how did it 'take out numerous
>>>components' if there was no load on it?
>>
>>
>> It is abbreviated, it took a while to figure out what components had failed
>> etc. and then tell the supplier about it.
>>
>> The fault took out numerous components because that is in the nature of
>> some SMPS designs when there is no load, and that's why it was returned.
>
>Sorry, but I still don't know what that means: "the nature of?"
>
>You mean components in the PSU? not other components it was (not) connected to.
>
>> If
>> it had been a simple blown fuse, then it'd be a patch it and use it fix.
>> As it was, there were a number of semiconductors failed, looking at the
>> replacement cost (plus risk of repeat performance failure), it was easier
>> to just return it.
>>
>>
>>>Once the output is clamped the story is over: it's shutdown; no
>>>'on-off-on-off-on-off...'. OCP doesn't release till input power is removed.
>>
>>
>> Depends on design, surely?
>
>It is, of course, always possible to do it wrong but, to use your term, it
>is 'in the nature of' <g> the situation itself. Consider designing one that
>'resets' automatically. It would ALWAYS oscillate (on a fault) since the
>clamp, by definition, will put the output back into the 'safe' area causing
>removal of the clamp which will then let the output go back to fault which
>will cause a trip which...
>
>I can't imagine why anyone would think that is 'desirable' operation (it
>isn't as if this is a pole power line where we're burning off tree branches
>with breaker reclosures) and, with that as (not) a criteria, there's just
>no 'right way' to make one that resets as a result of it's own clamp action.
>
>> I've seen other PSUs keep tripping and restarting
>> when overloaded or "under" loaded.
>
>Sounds like a logic error in the design then, or some odd and unforeseen
>anomaly was causing it.

Every packaged PSU module we have used has worked that way - Our
product goes into industrial sites, and it is an unfortunate fact of
life that accidental human-induced faults do happen occasionally, and
in those cases we do want the SMPS to keep trying to bring up the
line, as long as there is no damage. If it needed power removed before
power would be restored, THAT would be a "logic error" and a major
PITA for our customers.

Tony (remove the "_" to reply by email)

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