On a Design of Adjustable Passive Balancing Circuit Using PWM Technique for Li-Ion Battery

For the conventional passive balancing circuit in Li-Ion battery packs, one constant bleeding resistor and one switch are used for draining excess energy of one battery cell. Using the PWM (Pulse-Width-Modulation) switching technique for controlling the switch, one can vary the drained power by adjusting the duty cycle and switching frequency. This paper studies the design constraints of the passive balancing circuit for being used with the PWM switching technique. Normally, the bleeding power for the unity duty cycle must be set first as high as possible. Bleeding power can be varied by adjusting the PWM duty cycle. For draining high power or current, the MOSFET switch could run into the linear region causing the excessive losses on the MOSFET. The experiments are carried out to demonstrate the behaviors of the passive balancing circuits. As the study results, guidelines and recommendations are given for optimal designs of high power PWM passive balancing circuit.