Lack of space on a cheap signal line protector PCB (surge filter/diverter)
is one excuse I've made for using track fuses.
On a side note: thermal fuses fail *short circuit* (never open due to
ambient heat) after being subject to 3kA 8/20uSec pulses!!!
-----Original Message-----
From: van de Werken, Matthew (DEM, PH)
[mailto:[EMAIL PROTECTED]]
Sent: Friday, 15 June 2001 12:35 PM
To: 'Protel EDA Forum'
Subject: Re: [PEDA] AW: Spiral trace construction?
> -----Original Message-----
> From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
> Sent: Friday, 15 June 2001 12:28
> To: "Protel EDA Forumm"@bastion.qld.csiro.au;
> [EMAIL PROTECTED]
> Subject: Re: [PEDA] AW: Spiral trace construction?
>
>
> At 01:15 PM 6/14/01 -0500, David Cary wrote:
> >In my case, I
> >finally got enough documentation to prove that PWB traces
> varied in resistance
> >far more than the 1% we wanted in our current-sense
> resistor. (Mostly due to
> >variations in the tin plating over copper, I hear).
>
<snip>
>
> That might be usable as a sense resistor, even for accurate
> measurements,
> if it could be trimmed or calibrated. The variation of
> resistance with
> temperature would need to be considered. There might be
> applications where
> this would make sense.
>
Maybe it would be feasible to set-on-test a system whereby the sense
resistor section is tapped off one of several places on the sense trace (or
one of several pads is joined):
Sense track:
++++========||||||=========|=========+++++
|||||| |
pads--------^
That way, you could choose which point at build time is the ideal spot. This
wouldn't be ideal, but it would make it easier to allow for variations in
manufacturing.
> Using thin track as fuse is a well-known bad idea, precisely
> because of the
> problems noted above plus a few, though, again, even bad
> ideas can have
> their day.
>
I can't think of a single good use of using a track as a fuse - if the
"fuse" blows, you basically have to toss the board. Surely it would be
(marginally) better to use a low-ohm resistor as a fuse?? Of course, the
ideal situation is to use a fuse as a fuse, but as we all know we don't
always live in the ideal world...
Cheers,
MvdW
> [EMAIL PROTECTED]
> Abdulrahman Lomax
> P.O. Box 690
> El Verano, CA 95433
>
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