Patent ID: 8779722

Claim:
A two-stage charge equalization apparatus for a battery string having two or more battery cells connected in series, comprising: a two-stage DC-DC converter including a first DC-DC converter which is inputted with a total voltage of the battery string and outputs a voltage lower than the voltage inputted; and a second DC-DC converter which is inputted with an output of the first DC-DC converter and outputs a charge current for charging a particular battery cell, wherein the battery string is divided into one or more battery modules having a plurality of battery cells connected in series and the second DC-DC converter is provided for each battery module; a current conversion switch module which forms a path of the charge current between the battery module and the second DC-DC converter to allow the charge current to be applied to the particular battery cell composing the battery module and controls an application direction of the charge current; and a microprocessor which determines a battery cell to be charged of a low-charged battery cell and controls the current conversion switch module to allow the charge current to be applied to the battery cell to be charged.