Randall R Schulz wrote:
On Thursday 14 February 2008 12:26, James Knott wrote:
...
Quite so. I was just replying to that transformer comment. With switching supplies, transformers are often not used on the input. The incoming AC is rectified, filtered and the resulting DC is used to power the switching regulator that provides the desired output ...
Yowsa!
What about the isolation provided by a transformer on the input? How do these things get UL (or other regulatory agency) approval?
I guess you've forgotten about those old 5 tube AC-DC radios, that ran directly off line power, without any power transformer whatsoever. It's entirely possible to design and build a safe power supply, without using any transformer, provided there's appropriate electrical isolation between the supply, exposed metal parts and the load. As mentioned in another note, switching power supplies have a transformer that's used to covert the high frequency oscillator power to a lower voltage. The fact that there's a rectifier and capacitors ahead of the transformer doesn't make it unsafe. All that required is proper isolation techniques be used. Don't forget, a line frequency transformer, that can handle a few hundred watts, will be large and heavy. -- Use OpenOffice.org http://www.openoffice.org -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org