Doug,
To answer your question of which is better:
The primary concern should have been the temperature of the windings
to see if the insulation (between primary and secondary?) would have
exceeded the allowable limits and thus possibly break down.
A (much lesser) secondary concern would have been the risk of a fire
starting either in the transformer or in other components due to the
heating of the transformer.
Glenn Lesmeister
-----Original Message-----
From: dmck...@paragon-networks.com
[SMTP:dmck...@paragon-networks.com]
Sent: Tuesday, September 16, 1997 5:35 PM
To: IEEE Product Safety Technical Committee -
Subject: Re: EN 60950 and component heating
Hi Kevin,
I had a rather bad experience between UL and CSA in
the older days when there wasn't so much discussion
and agreement between them. I had set up an MOU
between them with UL as the test location.
Went like this ...
Switching power supply. Has a transformer.
Must do abnormals on it. UL does the abnormals.
Temp probe on the *windings* of the transformer.
CSA said, "No way. Since the real concern is
the PCB flaming from over temps
from the transformer, we want the
probes on the *bobbin*."
UL said, "No way. Since the real concern is
what generates the heat, we want the
the probes on the *windings*."
To this day, I can't say absolutely which way
is the better.
Guess I didn't help you much either.
Regards, Doug
> From: Kevin Harris <harr...@dscltd.com>
> To: EMC-PSTC (E-mail) <emc-p...@ieee.org>
> Subject: EN 60950 and component heating
> Date: Monday, September 15, 1997 6:14 PM
>
> Hello All,
>
> In testing some product for excessive temperatures I have come up
> against the following problem. Consider a diode (part of a bridge
> rectifier circuit) and the PCB underneath the component. If one
measures
> the temperature of the diode it does not come close to the
specification
> for the part. However if we place a thermocouple on the pad where
the
> diode is attached to the PCB and we consider that as a temperature
> measurement for the PCB material itself ,then the temperature
obtained
> is above the board manufacturers spec of 110 C (when we take into
> account our maximum permissible ambient temperature of 49 C). By
the by
> all this is NOT operator accessible if that makes any difference.
>
> Questions.
>
> 1. Is this a valid temperature measurement for the PCB? I'm of two
minds
> on this. It could said that I'm really measuring the diodes
temperature
> and not the PCB. On the other hand the diode pad does touch the PCB
