The MB3873 is a pulse frequency modulation (PFM) type multi-resonance AC/DC converter IC providing soft switching functions in a more compact, higher-efficiency, low-noise package. Since this product allows reduced number of the components and reduced size of the transformer, it is also compatible with the miniaturization of AC adaptor. The product retains the multi-resonance for the non-load, over-load and load short-circuit over the wide range of input voltage, making it the appropriate IC for the small-sized AC adaptor.