Basic knowledge of lithium battery protection board

Date:2019-04-01 16:57
1、 Composition of protective plate
The reason why lithium batteries (rechargeable) need protection is determined by their own characteristics. Due to the material of the lithium battery itself, it cannot be overcharged, discharged, overcurrent, short circuited, or charged or discharged at ultra-high temperatures. Therefore, the lithium battery components always appear with a delicate protective plate and a current protector. The protection function of lithium batteries is usually completed by the cooperation of the protection circuit board and PTC. The protection board is composed of electronic circuits, which accurately monitor the voltage of the battery cell and the current of the charging and discharging circuit at all times in an environment of -40 ℃ to+85 ℃, and control the on-off of the current circuit in real-time; PTC prevents severe damage to the battery in high-temperature environments.

The protection board usually includes control ICs, MOS switches, resistors, capacitors, and auxiliary devices such as NTC and ID memory. Among them, the control IC controls the conduction of the MOS switch under all normal conditions, allowing the cell to communicate with the external circuit. When the cell voltage or circuit current exceeds the specified value, it immediately (tens of milliseconds) controls the MOS switch to turn off, protecting the safety of the cell. NTC is the abbreviation for Negative temperature coefficient, which means negative temperature coefficient. When the ambient temperature rises, its resistance value decreases, and the use of electrical or charging equipment responds in a timely manner and controls internal interruptions to stop charging and discharging. ID memory is often a single line interface memory, which stands for Identification and stores information such as battery type and production date. It can limit the traceability and application of products.

2、 The main function of the protective board
Generally, it is required that the Control (IC) detects the voltage of the control cell and the working current and voltage of the charging and discharging circuit between -25 ℃ and 85 ℃. Under all normal circumstances, the C-MOS switch transistor is turned on, so that the cell and the protection circuit board are in normal working conditions. When the cell voltage or working current in the circuit exceeds the preset value of the comparison circuit in the control IC, the CMOS is turned off within 15-30ms (different control ICs and C-MOS have different response times), Close the discharge or charging circuit of the battery cell to ensure the safety of the user and the battery cell.

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