There is a reason why fuses cost as much as they do:
1) Their fusing current vs time (what is called I-squared-T curves) is well defined, repeatable across the population and consistent, even with temperature changes.
2) Their clearing current capacity...don't confuse the fusing current with clearing current. Once that a fuse opens, an arc will form. If your power source has enough energy capability, this arc will not dissipate on its own, but it has to be quenched. True, give it enough time and it will quench on its own, but not after having burned something up.
As I explained, my personal experience was with a cheap Chinese CFL. It cost me US$1 each back in the late 1990s which was a bargain.
I was working on my computer at home, when something shorted inside the CFL. A loud bang, and lots of acrid smoke started coming out from the light fixture. Fortunately, I was there and knew exactly what to do, turn off the light switch.
Had the room been alone or with my wife there, she would just have panicked and ran.
When I performed an autopsy on the unit, I found the brown paper phenolic PCB, which I don't think meets UL94-V flammability ratings, had an almost 1 cm wide burnt area.
I removed and threw away all the lamps I had purchased.
In over 30 years I have never seen a PCB trace used as a fuse, I would never do it and all designers I know would never do it...
Basic thoughts, a fuse is deigned to do a job, they are tested and certified, a PCB trace used as a fuse is not tested so you are relying on an untested and unreliable PCB trace to fuse to prevent damage due to some high current incident...
Not a good idea.
I've seen traces used as fuses, but only in cheap, throwaway Chinese products.
In the particular instance, it was an inexpensive CFL.
The only reason not to use a fuse is because you intend the product to be disposable. And save a few pennies.
I would be very cautious of this statement. It may well be true if the circuit is still working to some extent that it can limit the current itself draws, but there are many failure scenarios that are external to the circuit (for a silly example: someone sticking a screwdriver across the power regulator input terminals) where the current can be way above the designed maximum.Modern designs tend to self-limit (current) and hence fuses are slowly becoming redundant- less and less instruments now depend on fuses for protection.
Modern designs tend to self-limit (current) and hence fuses are slowly becoming redundant- less and less instruments now depend on fuses for protection.
Which particular standards say that a PCB trace cannot be used as a fuse ??
Standard no, section no please?
Many branded (very respectable American and European) TV brands (CRT type, older models) I have seen used paper phenolic PCB boards.
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