A constant voltage transformer, commonly called a CVT, is a ferroresonant transformer that maintains a nearly constant AC output voltage even when the incoming supply voltage varies.
Unlike an ordinary transformer, which primarily changes or isolates voltage, a CVT combines transformer windings, a magnetic core, and a resonant capacitor circuit. This arrangement provides voltage regulation, electrical isolation, and power conditioning within a single unit.
The primary and secondary windings are physically and electrically separated. This galvanic isolation helps prevent high-frequency interference, spikes, and disturbances present on the incoming mains supply from reaching the connected equipment. It can also prevent electrical noise generated by the load from traveling back into the supply network.