The Li-Ion rechargeable battery is managed so that it will not occur over-charged or over-discharged status. On the battery management system, there is a primary protection circuit and also the secondary protection circuit that would back up when the primary protection circuit fails. By the double protection circuit, BMS has redundancy and secures safety.

A state in which the primary protection circuit fails is an obvious abnormal and must make disable the battery pack to prevent any risk of danger.

 

The standard circuit scheme of the secondary protection circuit uses a secondary-level voltage monitor IC and a fuse, called three-terminal fuses, signal fuses, and fusing registers. When the voltage exceeds the threshold value of the predetermined voltage and is held for a certain period of time or longer, the fuse cut off the power path and prevent overcharging and over-voltage (See the figure below)

 

 

 

The double protection circuit on BMS is already standard for the notebook PCs, Energy Storage Systems, the large stationary battery systems, UPSs, the electric bicycle, etc. to ensure safety.

In recent years, many rechargeable battery products have the double protection circuit in order to meet the requirements of the safety standards.
Uchihashi  -   Three Terminal Fuse

１．Fuse off the power path physically in overvoltage status

２．Large current and high voltage rating, no required parallel use of the fuse

３．High Reliability and Durability in the battery management systems