Buck-Boost Transformers are small single phase transformers designed to reduce (buck) or raise (boost) line voltage from 5-20%. The most common example is boosting 208 volts to 230 volts, usually to operate a 230 volt motor such as an air-conditioner compressor, from a 208 volt supply line.
Buck-Boost Transformers are an economical way to correct a potentially very serious problem. Anytime a line voltage change in the 5-20% range is required, a Buck-Boost Transformer should be considered as your first line of defense.