switchmode AC adapters

[Jamie Morken]

Hi all,

The newer AC adapters for printers/laptops etc seem to be a lot lighter and
higher power output than older AC adapters. Is this due to them being
switching powersupplies instead of 60Hz stepdown transformer based? Also to
make a switchmode 120VAC to ~12VDC isolated power supply requires quite a
few components: input diodes, mosfet half-bridge, HF transformer, output
diodes, and the control circuitry. Do the switchmode AC adapters implement
this type of design or are they using a simpler/different design?

cheers,
Jamie Morken

 

[Joerg]

Hi Jamie,

Yes, these are switchers. The size reduction of the transformer saves
more money than the extra parts in there. Then there is shipping weight.
Just imagine how much half a Dollar savings in freight charges means.

When you open one you'd be surprised. Often there are no fancy FETs,
they use whatever is lowest in cost. Every component gets turned around
and around to see whether another penny can be squeezed.

Believe it or not, it is actually fun to design with a rock solid cost
target. You get used to it really fast.

Regards, Joerg