Description of why a fuse blows

[johnnydiaz]

I have always heard that if a fuse violently blows its due to a mosfet or bridge rectifier. Can someone explain this in detail. Why would the mosfet or bridge rectifier fail and how does the fuse blow up? Sorry for the newbie question.

Thanks,
Johnny

[370forlife]

Re: Description of why a fuse blows

If a fuse blows, it is because something is drawing more power through the fuse than what it is capable of carrying.

I.E. in a power supply a MOSFET on the primary acting as a primary switcher. For some reason, the MOSFET blows up, shorting itself out. This short tries to pull more current through the fuse than what the fuse is rated for and the metal filament in the fuse gets so hot that it melts itself and cuts the power.

[twbranch]

Re: Description of why a fuse blows

Wow a pretty good explanation! Now can you explain how a transistor works?...hahaha! Not trying to hijack just some people can't explain it and that was a good explanation of simple component in my opinion!

[370forlife]

Re: Description of why a fuse blows

http://www.youtube.com/watch?v=-td7YT-Pums

This is a pretty good video.

[ben7]

Re: Description of why a fuse blows

Basically, the larger the short circuit is, the faster/more violent the fuse will blow, because the immense current heats up the fuse link very fast. Sometimes so fast that the fuse link actually vaporizes in plasma, which expands violently, causing the fuse glass to shatter!

You can make a fuse link glow by giving it just enough current, not enough to make it melt in two.

Fuse link - the wire inside the fuse which melts and interrupts the circuit.

[mariushm]

Re: Description of why a fuse blows

I personally have a hard time remaining with some knowledge from those Make videos where that Colin guy appears.

The videos are somewhat empty in actual information and in a way, I almost can't stand him (he pauses a lot in the videos as if he just said or is about to say something intelligent, it's annoying to me)

I found these to be better to understand what transistors are (well, the most common transistors) :

SparkFun According to Pete 7-5-11: Diodes and Transistors

a very easy to follow explanation of diodes and the common transistors, with simple words :

http://www.youtube.com/watch?v=w9cd7B5QRRo

Tutorial: How to design a transistor circuit that controls low-power devices

http://www.youtube.com/watch?v=8DMZSxS-xVc

a "hands-on" practical example where the guy explains and does the math to show you how to use a transistor to turn on and off something

Some more technical videos about the operating modes of a transistor (linear mode, cut-off mode, saturation mode)

Introduction, explanations : http://www.youtube.com/watch?v=HVECDUeJRw8
Saturation mode: http://www.youtube.com/watch?v=MSYHjMMgQd4
Cut-off mode: http://www.youtube.com/watch?v=61sBLBr-_OA

[tmiha71]

Re: Description of why a fuse blows

For some reason, the MOSFET blows up, shorting itself out.

Energy needed to blow fuse is for few orders of magnitude lower than energy needed to blow (explode) MOSFET (fuse WILL always blow /explode/ first, compared to MOSFET, will preserve MOSFET )...
Explosion usually breaks connection, so if MOSFET blows /breaks connection/ fuse can survive dissaster...

It'll be better to say, "..., the MOSFET did not close, when it had to, current rised,..."

But, if MOSFET is blown...
Reasons for blown (exploded) MOSFET are :
- excessive voltage (above rating)
- excessive current (above rating)...

And this (excessive) energy CAN NOT came through fuse (purpose of fuse)...

If it did not came through fuse, that speaks of some unwanted effects (LC circuit) which are pretty STRONG...