Why AC to DC are transformer based, mostly?

[_]

well in fact one of my projects that i wanted to operate from 240VAC, i wanted to be light-weighted and cheap and plus the circuit needed like a few tens of mA, so i decided to stick with a voltage divider, and then full bridge rectifier, and then voltage regulator.

it worked exactly as expected as in theory, but the amounts of heat that it generate were way above what expected, after one hour of operating the circuit, some plastic parts of the circuit melted.
also the circuit was extremly un-safe to operate, there was no protection what so ever.

do not implement any AC> DC converter without a step down transformer (unless its SMPS), unless your circuit consumes less than 1mA and you know exactly what you are doing, and even though you are puting your life at risk, so don't do it anyway.

 

[Naveed Alam]

There are non-transformer AC->DC adaptors, but I dont see them much around...

Why every mobile/etc. uses charger with a transformer inside? just a couple of resistors +diodes would not be enough?

at least for mobile chargers with small sizes, and small ratings.. it seems impossible to do it without using voltage down converter transformers..
as u said u saw non-transformer ac-dc devices; then it must be huge and rating must be hight

Regards

 

[rituparnasaikia]

Can be used a BUCk converter with the efficiency of more than 90% but it will be costly so the transformer.
In place of these capacitors and diodes can be used but its not that safe.

 

[tamerakshar]

if you don't use a ransformer the circuit outputs won't be isolated from mains (electric shock hazards),the output voltage is relative bitween the output pins;i mean none of the out pins is really ground.
it acts like virtual relative ground to the other pin.
i mean none of the pins have a zero voltage reading.
actually its a safety criterion fellaz.
TeE ThE EdE

 

[rami.masadeh]

i think that it used for safty,and for step down the voltage, it is better than used capacitor and resisters because the loss in these