Fuse in small power supply needed?

[Lee Leduc]

Here is a typical 3 terminal regulator based dual power supply schematic that can be found on the net. It's used to power Op Amp breadboard circuits.

Is a Fuse required in the low voltage winding of the wall transformer or is it optional?

 

[Benta]

Is a Fuse required in the low voltage winding of the wall transformer or is it optional?

No, it's optional (and not really needed, small wall-wart transformers are usually short-circuit proof).

Primary side fusing is mandatory for fire protection, but I expect the wall-wart has this.

[danadak]

I may have been around too long but nervous about quality of wall warts
coming out of far east. I would advise a fuse. I have had more than one
melt plastic due to faults not properly addressed.


Regards  Dana.

[Lee Leduc]

I found a site with an article entitled "Engineering with wall plug-in power supplies and AC adapters". It mentions internal fuses.

https://www.powerstream.com/Wall-mount-FAQ.htm

"Internal fuses
Those wall plug-in power supplies certified by safety agencies are required to have an internal fuse to protect against fire if there is a short circuit. They are almost always soldered-in glass tube type fuses, and are almost never user replaceable. They are protecting the primary side of the transformer, so are typically rated at 240 volts. Don't get confused by this rating, even a 110 volt input wall mount transformer will use a fuse rated at 240 volts. The current rating is typically two to three times the rated input current."