If I was building a power supply for a circuit (just a simple mains voltage -> transformer -> bridge rectifier -> filter capacitor -> linear regulator), where would be the best place to put an on/off switch? Part of me would say on the low voltage side for safety, but a lot of circuits seem to put it on the primary side of the transformer (which makes some sense as this stops the transformer being energised). Also, if it is on the primary side, should it be on the live/hot side or the neutral side ( or does it not make a difference?)
Cheers!

 

In the "live" side of the mains power.

 

I put a toggle switch in the Line side (Blk wire in the US) in the transformer primary. I also add a fuse holder downstream of the switch.

Leaving the transformer primary energized 24/7 wastes power, makes heat, makes acoustic noise.

 

Switch the high side of the mains and then as mentioned a fuse is a nice touch (actually good practice).

While switching the low side sounds lucrative it really isn't safe. Matter of fact it can be dangerous and would be poor practice to switch the low side.

Ron

 

And of course if powering off of a 13a socket, you could fuse it appropriately there in the plug.
Max.

 

fuse it appropriately there in the plug.

I have a 20 inch fan with the fuse in the plug, but I consider it a form of sabotage. Hide the fuse so ignorant people can't figure out why the fan won't run...then buy a new fan.

Anyway, if you find a 20 inch fan, you might find a power plug with a fuse hidden inside it.

 

OP is from UK.
In the UK this is normal installation practice of 13 amp outlets the plug of which are fitted with a independant fuse for each appliance the plug is fitted to.
The reason being that the plug circuit is fed from a 30amp breaker.
Max.

 

I have a 20 inch fan with the fuse in the plug, but I consider it a form of sabotage. Hide the fuse so ignorant people can't figure out why the fan won't run...then buy a new fan.

Anyway, if you find a 20 inch fan, you might find a power plug with a fuse hidden inside it.

The same with some Christmas lights, not that anyone fixes them anymore..

 

In the UK this is normal installation practice of the plug of which are fitted with a independant fuse for each appliance.

Yeabbut..do they hide the fuse so most people have no clue it's there?
Your statement seems to say everybody knows about the fuse. Is it usually replaceable?

 

Everybody should know about it by now, its been that way for >60yrs!
It is a simple replaceable fuse.

Max.

 

My fan only has a molded plastic plug with no hint anything unusual is in there. No way to dismantle it. No extra bumps. Just a note in the Users Guide, which most people immediately toss in the bin.