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What alternatives are there to polyfuses?

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Plecto

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Hi. I need a way to protect my amplifier against over-current conditions. Are there semiconductors that can break the circuit at a set current and auto reset after a set time? If so, what are they called?
 

Also called "Fusible resistors".
We looked into them before but they come with a very wide tolerance on the 'actioning current', and also they have considerable delay till acting, so they arent that great.
Your better off doing your own current clamp with eg a FET and a BJT. or FET and comparator....or fet switch and a current monitor like one of the diodes.com ones.
 

Hi;
"Load switch" term is also used for similar semiconductor cct.
 

I've done some more research. Will a fast acting SMD fuse blow before a TO-220 transitor blows? If I can't rely on that I'm not sure what to do. A current limitert will work, but if a fault happens, the current limiter will dissipate a huge amount of heat which again. This will make it do thermal shutdown cycling, which is not good for this particular project. What other options are?
 

Will a fast acting SMD fuse blow before a TO-220 transistor blows?
A very unspecific question, unfortunately. What's the transistor operating point, what's the load (short or overload)? You need to look at transistor SOA curves and fuse characteristics.

Does the amplifier use current limiting, possibly with fold-back characteristic?

A current limiter will work, but if a fault happens, the current limiter will dissipate a huge amount of heat which again. This will make it do thermal shutdown cycling, which is not good for this particular project.

Why "not good"? Too lazy to design it?
 

You originally ask for a self-resetting "fuse". Polyfuse
in ICs is not that, it's a fuse kind of fuse.

There are chips that try to act like circuit breakers.

There are many power driver type parts which have
built in current limiting (some plateau, some foldback,
some timeout and reset). Many ways to implement
current limiting, depending on what you really need
to happen.
 

Coordinating the protection of a fuse's I2t curves with a transistor's SOA requires lots of work.
On one hand, you don't want nuisance tripping when playing loud levels. On the other, you want the semiconductors to be protected.

But even then, it is far easier with a fuse than with a Polyfuse. Not only polyfuse's trip current highly dependent on the ambient temperature, with each tripping event their characteristics start to shift.


OT: that is the reason, when the first solid-state power amps were introduced, that vacuum-tube enthusiasts would sneer at them.
If you overload a vacuum-tube amp, you have a long time before major damage occurs, and then a fuse protection was very simple to implement.
 

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