basic question about "switching power supplies"

Jun 08, 2006 4 Replies
G

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



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P

Yes.

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

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R

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

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G

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

Gav

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D

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.

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