Quote:
Originally Posted by Lynx-lynx
Are the transformers still required for wall charging?
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What do you mean by that question?
To charge a reader or a phone or any piece of small electronics nowadays you usually require 5V Direct Current, usually written 5V DC.
Socket on the wall has Alternating Current AC, usually 230V or 110V nowadays.
In the "Goode Olde Dayes" you needed a transformer, a rectifier (four diodes) and a capacitor to smooth the current out. In a typical transformer, running of the mains with 50 or 60Hz frequency you had to have a number of windings in a primary and secondary coil in the same ratio as the input output voltage. Sometimes you had transformers that had a switch attached that allowed you to select output voltage by engaging additional windings in secondary. Sometimes you had a switch between 110 and 230V that would select two different primary windings. (220V would use the whole primary, 110V position would use just half the windings).
Nowadays, we have switching supplies. They contain a transformer too, but the transformer is much smaller and we do not switch between different number of windings to select (or regulate) output voltage. The primary of that transformer is fed by electronics that rectifies and smoothes the input voltage and then feeds a high-frequency pulses. The output of the transformer is measured and the feedback is used by that switching circuit to make the pulses that feed the primary wider of narrower. The result is that the modern power supplies are much, much lighter and can produce exact 5V (or any other arbitrary value) even with widely changing input. That is why you need just a simple wall socket interface and the power source for your mobile phone of a reader or a notebook can work with any mains voltage and frequency in the world. The transformer inside can be much, much smaller (reducing the amount of iron for core and amount of ever-more-expensive copper). You can see the difference best with the new "inverter" welders. Old ones were difficult to lift by a strong man, new ones are unbelievably light. The transformer can be smaller, because it works on much higher frequency.