[SI-LIST] Re: Can a thin PCB trace be used as a reliable fuse

Hi Tilak,

I have thought about this myself in the past - the PCB lends itself to
many such things, like built in resistances, capacitances, inductances,
even batteries - but see some problems other than those already =
mentioned:

1. PCB manufacturing tolerances - particularly in the case of tracks
   on the outer layers, plating will vary from area to area, and
   board to board, so that even the current threshold will not be
   100% predictable. Also tracks on inner layers will have different
   temperature characteristics, obviously.
2. Performance of PCB 'fuse' - will this really meet your _specifc_
   performance needs, not just current threshold?
3. Perhaps worst of all - environment: you would be depending upon the
   destruction through heat of a copper trace. The environmental effect
   upon exactly what current in a specific situation would be needed,
   would be considerable, unless you can guarantee a very small window
   of operating temperatures.

It could be possible to use a different process, such as carbon printing
(usually used for coating the contacts on keyboards, for example), to
'print' a certain resistance onto the board. This may solve problem 1,
perhaps part or all of problem 2, but you still have problem 3 to deal
with - unless you build in the 'extra feature' of air conditioning ;-)

The suggestion that you may find a 'real' component small enough is
definitely worth chasing - the 'Littelfuse' range includes some pretty
small fuses (the internet is 'worth its weight in gold' in this respect =
-
go google it).
____________________________________
Sol Tatlow, M.Eng. (Oxon)
ProDesign Electronic & CAD Layout GmbH
Product Developer
Albert-Mayer-Str. 16
D-83052 Bruckmuehl
Phone: +49 (0) 8062-808-302
Fax:   +49 (0) 8062-808-333
Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx
www.prodesign-europe.com
____________________________________=20

-----Urspr=FCngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
Im Auftrag von Gaitonde, Tilak
Gesendet: Mittwoch, 25. August 2004 12:17
An: Si-List
Betreff: [SI-LIST] Can a thin PCB trace be used as a reliable fuse


Hi Masters,

This is really not an SI related query, but comes under electronics =
design.=20
My query is this. Can a thin PCB trace be used as a reliable fuse. I =
have a
real estate problem on my PCB & require 4 fuses with current threshold =
of
6A. I searched for the components & found they too huge to use on the =
PCB.
So thought I can use trace as fuse!!=20
If it is possible is there any paper that has this explained?=20

Please help.

Thanks,

Tilak
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