The reason why lithium battery packs need protection is determined by their own characteristics. Since the material of the lithium battery pack itself determines that it cannot be overcharged, overdischarged, overcurrent, short-circuited and ultra-high temperature charging and discharging, the lithium battery pack always appears with a delicate protective board and a current safety device. 

   The protection function of lithium battery packs is usually completed by the protection circuit board and current devices such as PTC. The protection board is composed of electronic circuits, which accurately monitors the voltage of the cell and the current of the charging and discharging circuit at an environment of -40℃ to +85℃, and controls the on and off of the current circuit in a timely manner; PTC prevents harsh damage to the battery in a high-temperature environment. 

   The ordinary lithium battery pack protection board usually includes control IC, MOS switch, resistor, capacitor and auxiliary devices FUSE, PTC, NTC, ID, memory, etc. The control IC controls the MOS switch to conduct under normal circumstances, so that the battery cell is turned on with the external circuit. When the battery cell voltage or circuit current exceeds the specified value, it immediately controls the MOS switch to turn off to protect the safety of the battery cell.

    Under normal circumstances of the protection board, Vdd is high level, Vss, VM is low level, DO and CO are high levels. When any parameter of Vdd, Vss, VM is converted, the level of the DO or CO terminal will change.

https://www.custom-battery-packs.com：Custom Battery Packs  Battery Packs  Custom Batteries