Apparatus and method for diagnosis of cell balancing circuit using flying capacitor

PURPOSE: A breakdown diagnosis apparatus of a cell balancing circuit and a method thereof are provided to prevent the malfunction of a battery pack due to over discharge by easily diagnosing the malfunction about a cell balancing circuit. CONSTITUTION: A floating capacitor(C1,C2) is connected to the voltage sensing line and charges the voltage of each battery cell. A cell voltage sensing circuit(20) senses the charging voltage of the floating capacitor corresponding to each battery cell through the voltage sensing line. A cell balancing circuit(30A,30B) is connected to both ends of the floating capacitor and discharges the floating capacitor. A controller(40) distinguishes the malfunction of the balancing circuit based on the charging voltage of the sensed floating capacitor.