# basic question about "switching power supplies"

Discussion in 'Electronic Basics' started by [email protected], Jun 8, 2006.

1. ### Guest

hi all - sorry if this is trival but not found much useful info....

I have many devices whos power supplies have such info as 50-60hz and
110-240V printed on them (eh mobile phone charger, mp3 player). Am I
correct in saying that this essentailly means the device will be fine
in pretty much any country where the frequency and voltage are within
those ranges without anything other that a travel plug adapter?

I understand the above is called a "Switching power supply".

If thats the case, are step up/step down transformers only ever
required for devices that have adapters/supplies that say (for example)
60hz, 240v - i.e. linear PSUs?

I know it sounds simple but I just want to check before I go and blow
anything up accidentally

thanks!

Gav

2. ### Pooh BearGuest

They are indeed. You could actually make a 'conventional' psu that does this but
it's exceedingly rare.
Transformers are need for fixed voltage devices used other than their home
territory. The 50/60 Hz issue is rarely a problem but can sometimes be for 60 Hz
devices used on 50Hz.
Sensible.

Graham

3. ### Rich GriseGuest

Not to worry - that's what sci.electronics.basics is _for_.

And yes, as Pooh Bear said, all of your guesses are right.

Cheers!
Rich

4. ### Guest

Hey guys!! thanks very much for the responses - very helpful!

Gav

5. ### Dr Engelbert BuxbaumGuest

Yes, that is the idea. A switching power supply rectifies the input
voltage (so you are independent of grid frequency) and then generates a
high frequency (several 10 to several 100 kHz), high voltage AC which is
fed into a transformer. Because of that high frequency, this transformer
and the capacitors that smooth the rectified output voltage can be quite
small. The circuit that generates the AC is controlled by the output
voltage, so that can be independent of the input voltage over a fairly
wide range.

The important thing is to never open a switching power supply unless you
really know what you are doing. There are capacitors inside charged with
several hundred Volt DC that can bite you long after the device has been
separated from the grid.