Posted by electro on November 05, 2019 at 14:13:42 from (204.116.78.143):
In Reply to: Question for JohnT posted by moonlite37 on November 05, 2019 at 04:16:06:
Just a few comments:
As others have said, switch mode power supplies have been around much longer than me, first as mechanical vibrators with either electrical or mechanical rectification, then with solid state devices. They are not new but offer some advantages over linear power supplies and are now very common with the advent of inexpensive components.
The few wall wart power supplies I have unpotted were all just transformers and rectifiers. I am sure there are some that use a switched mode power supply but I expect most are just older linear supplies.
I doubt there are any grid power lines using "millions of volts" AC current. Most are going to be 500K or less although there are a few DC lines that may reach a 1000K but I do not know if there are any in the US. There are some lower voltage DC lines in the US.
I have not seen any real studies that link 60 cycle magnetic fields from living under a power line to any forms of cancer. I would be interested to see any real peer reviewed studies that show that connection. A lawyer advertising on TV does not count as a medical expert.
The skin effect is real for 60 cycle current. Depending on the material the wire is made from the skin depth can be 3/8 of an inch or less. For high currents that depth becomes a problem. Power substations used to use hollow conductors at one time and maybe still do because of the skin effect at 60 cycles.
As Mark said, voltage doubler circuits were common at one time and were used instead of transformers in some low end radios and TVs. The basic circuit, a Cockroft Walton multiplier, was used to supply several millions of volts to early linear accelerators used for atomic research using essentially nothing more than diodes and capacitors.
With the advent of inexpensive power MOSFETs and IGBTs, these power supplies are very common and for good reason, they work well in a lot of applications.
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