Ferroresonant Transformers—Voltage Regulation by Magnetism

Here is more about ferroresonant constant-voltage transformers. Back in the day, many people called these “Sola transformers” after the company that dominated the market for them. Not only do they provide a constant voltage output for an input voltage range around 40% of nominal, they provide excellent surge suppression both due to the inductive momentum of the primary but also because they inherently re-generate the waveform in the secondary winding(s).