A high efficiency low cost direct battery balancing circuit using a multi-winding transformer with reduced switch count

This paper presents a simple circuit for balancing battery cells. The circuit is composed of one low voltage MOSFET for each battery cell and a multi-winding transformer for a group of battery cells. Only one identical gate drive signal for all the MOSFETs is needed to control the balance current. Energy can be directly transferred from higher voltage cells to lower voltage cells. The balancing circuit can achieve ideal balance results as long as the multi-winding transformer has ideal symmetry. Other circuit components´ asymmetry would only affect the balance speed. Simulation results are given to show the effectiveness. A circuit for balancing a four-cell battery group is tested. The experiment shows the energy transfer efficiency is up to 93% between cell energy transfers.