What is dc dc converter?

AC stands Alternating Current, a type of electricity that changes constantly from one polarity to another(like what you get from the wall outlets). DC stands for Direct Current, a type of electricity that maintains its polarity all the time(like what you get from a battery). AN AC/DC converter is something that turns outlet-type electricity into battery type electricity.
RECTIFIER s can convert ac to dc.the different types of rectifiers are halfwave,full wave,bridge rectifier.by connecting capactor to all of the above mentioned ckts efficiency can be enhanced.