Modern cellphone chargers are much lighter and less bulky than they used to be. I assume that this is because they no longer use a transformer with a metal core to step the voltage down. So how do they work?
鈥� The two replies published previously (Last Word, 21 April 2007) on the reduction in size of chargers contained factual inaccuracies. The size of a transformer is only inversely proportional to the frequency of the electricity supplying it if the flux density remains the same.
Second, ferrite is not iron filings glued together; it is a ceramic material where iron is combined with one of several metals 鈥� usually manganese or nickel.
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In addition, the transformer cores made of iron filings glued together are called 鈥渋ron powder鈥� and, finally, the transformer in a 鈥渟witched-mode鈥� supply is rarely torus-shaped.
Ian Benton, Ashton-in-Makerfield, Lancashire, UK
