13 Nov
2004
13 Nov
'04
6:36 p.m.
what you want to google for is "ferroresonant power supplies"
http://www.mcitransformer.com/i_notes.html
for example
A ferroresonant power supply is very similar to an unregulated power supply except for the
characteristics of the ferroresonant transformer.
The ferroresonant transformer will supply a constant output voltage over a wide variation
of the transformer input voltage. The problems with using a ferroresonant power supply
include that it is very sensitive to slight changes in line frequency and would not be
switchable from 50 Hz to 60 Hz, and that the transformers dissipate more heat than
conventional transformers. These power supplies are heavier and will have more audible
noise from the transformer resonance than regulated linear power supplies.