This paper presents a standalone analog active balancing circuit designed for series-connected Lithium-ion cells, which can be used together with an automotive battery management system (BMS). A very important parameter of the charging circuit, especially when it’s used for plug-in hybrid electric vehicles (PHEVs) or electric vehicles (EVs) is its efficiency, which affects both the capacity of the battery pack and its lifespan. Our proposed design is simple, derived from a boost converter and can be used either as a fully analog standalone circuit or it can be interconnected with microcontrollers or processors. In addition to this, another advantage over some different approaches is the ability of balancing the series-connected lithium-ion batteries during both charging phase and discharging phase, increasing their available capacity and preventing uneven and overdischarging for different cells. The proposed architecture was tested and validated using both simulation software and practical hardware implementation revealing that the obtained results were very similar to the initial expectations and calculations.

Keywords: Active balancing circuit, Battery management system, Boost converter, Charging circuit, Lithium-ion cells, Plug-in hybrid electric vehicles