How to improve the safety and reliability of battery pack
from：Pengwei New Energy published_at：2018-05-26 20:08:24 pv：1923
The protection of lithium ion rechargeable batteries must have the following 3 protective functions: 1. overcharge monitoring. To prevent battery deterioration, ignition and breakage, and ensure safety. 2. monitoring. Prevent battery deterioration and ensure battery life. 3. overcurrent monitoring. Prevent FET from damage, short circuit protection and ensure safety during handling. The protection circuit is used to realize the above three protection functions to improve the safety and reliability of the battery pack.
The function of overcharge protection is to prohibit the charger from continuing to charge when it reaches a voltage (hereinafter referred to as overcharge detection voltage), that is, to turn the overcharged FET into a turn off state, stop the flow of the charging current, and set the charge FET gate in the battery package to the off state to stop the charging. However, after overcharge detection, it must be guaranteed that the load can be discharged. By improving the error of overcharge detection voltage, on the one hand, the safety of the battery is improved (preventing the increase of internal pressure). On the other hand, the high capacity demand is required to improve its accuracy. In addition, overcharge detection is corresponding to pulse charging and misoperation due to noise, so delay time is required. The current protection IC can use the external capacitance to set the delay time freely.
The over discharge protection function stops the discharge of the load when the battery and voltage are low. The gate of the battery pack controlled FET is turned off and its discharge is forbidden. This process is just contrary to the action of overcharge detection. Since the battery voltage can not be lowered below the over detection voltage, it is necessary to require minimal protection current consumption at IC. Secondly, a lot of over put detection circuits have delay time.
The overcurrent protection function is to stop the discharge of the load when consuming large current. The purpose of this function is to protect the battery and FET to ensure the safety of the battery pack in the working state. Overcurrent detection means that the connection resistance of FET is treated as induction resistance, and the state of voltage is monitored. If the voltage is higher than the set voltage (overcurrent detection voltage), the discharge is stopped immediately. The delay time must be set for overcurrent detection. If there is no delay time, the overcurrent will be detected when the current suddenly flows in, and the discharge will stop. Therefore, the recent protection of IC can be divided into two different situations: short circuit and sudden current inflow. After overcurrent detection, the battery pack will be restored to normal after being separated from the load, and it can be recharged or discharged.