Electronetics has extensive experience designing and building CVT transformers
for a variety of applications and regulation profiles as tight as  ±3% over
wide line and load variations.
These highly specialized transformers are designed to enhance and control characteristics that are normally minimized. CVTs require highly controlled leakage inductance (the inductance that prevents any primary voltage from transferring to the secondary) in order to isolate the secondary from the primary. The leakage inductance is electrically connected to a capacitor that forms a resonant tank circuit causing the secondary portion of the magnetic core to saturate. Saturation, something to be avoided in other transformer designs, is exploited to force a maximum limit on the secondary voltage.
Electronetics designs CVT transformers for a wide variety of applications with regulation profiles as tight as ±3% with an input voltage variation as much as ±15%. The pros and cons of CVTs with this capability are:
Pros:
Good output regulation with no active circuitry
High reliability
Excellent primary to secondary isolation
Improved power factor on the primary even when the secondary is rectified and filtered
Excellent tolerance to continued short-circuit on the secondary
Cons:
Can be audibly noisy
Large size relative to power output
Requires separate resonating capacitor
Does not tolerate surge loads
Lower efficiency due to more core material and saturating part of the core
