I agree. You should use a real fuse if you need it to blow at a reasonably
accurate current. We do use PCB fusible tracks, but only to restrict the
area where the PCB track melts. That is useful for when the customer
replaces a fuse with a wad of aluminum foil or a soldered-on wire, without
determining the real reason for the blown fuse. When they apply power
again, the PCB fusible track melts, they send it back to us for repair, and
we replace the melted track with a soldered-in picofuse. So what we have
is a footprint for a picofuse, with a fusible track between the 2 pads.
Once the track is blown, a picofuse is soldered in to repair it. Zero
production cost, and it allows the board to be repaired even after customer
abuse. And they do abuse...
Best regards,
Ivan Baggett
Bagotronix Inc.
website: www.bagotronix.com
Brad Velander wrote:
Bob,
If you have not already found it, check out WWW.ULTRACAD.COM
Doug Brooks has studied and written several articles on this subject.
>From my own personal experience many many years ago, the fusible link is not
very reliable. It is only good as an absolute disaster stopping link that may blow
at 3 amps or may not blow until you reach 10 amps (we were trying to make it a 3
amp link). It may hang in there for 3 minutes at 8 amps as well. So don't expect
any fine tunability, too many variables and variances for great accuracy.
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
#14 - 1925 Kirschner Road,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Butcher, Bob [mailto:[EMAIL PROTECTED]
Sent: Friday, November 04, 2005 9:30 AM
To: [email protected]
Subject: [PEDA] How do I design a fusible link into a PCB?
I want to add a narrow circuit trace to a PCB design to act as a fuse.
It should operate with 1 Amp of current continuously and open if the
current exceeds a higher value (2-5 Amp). This project is very cost
sensitive and a 15 cent fuse may be too much. I have the guidelines for
conductor heating vs cross section, and it appears the conductor would
need to be less than 10 mils wide on a 1 Oz copper board. Does anyone
have experience with this subject?
Bob Butcher
[EMAIL PROTECTED]
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