The composition and main function of the battery protection circuit board BMS

This article mainly introduces the composition of the lithium battery protection board, the main function and working principle of the battery management system protection board.

Application range of lithium battery management system

* Lithium ion rechargeable battery

* Polymer lithium ion rechargeable battery

* Lithium iron phosphate rechargeable battery

Why do we say that the lithium battery must be used together with the lithium battery protection board BMS?

The reason why the rechargeable lithium battery needs protection is determined by its own characteristics. Since the material of the lithium battery itself determines that it cannot be overcharged, overdischarged, overcurrent, short circuited, and ultra-high temperature charging and discharging, the lithium battery will always be used with a well-designed protection board. The protection board is composed of electronic circuits, which can accurately monitor the voltage of the battery cell and the current of the charging and discharging circuit under the environment of -40℃ to +85℃, and control the on and off of the current circuit immediately; PTC prevents the battery from occurring in a high temperature environment Bad damage.

The composition of the battery protection board BMS

The protection board usually includes control IC, MOS switch, resistor, capacitor and auxiliary device NTC, ID memory and so on. Among them, the control IC controls the MOS switch to turn on under all normal conditions to make the cell communicate with the external circuit. When the cell voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off (tens of milliseconds). Protect the safety of batteries. NTC is the abbreviation of Negative temperature coefficient, which means negative temperature coefficient. When the ambient temperature rises, its resistance decreases. The electrical equipment or charging equipment is used to respond in time and control internal interruptions to stop charging and discharging. ID memory is often a single-wire interface memory. ID is the abbreviation of Identification, which means identification, and stores information such as battery type and production date. Can play a role in product traceability and application restrictions.

The main function of the protection board

Generally, it is required that Control (IC) detect the voltage of the control cell and the working current and voltage of the charging and discharging circuit at -25℃～85℃. Under all normal conditions, the C-MOS switch tube is turned on, so that the cell and the protection circuit board are in contact with each other. Normal working state, and when the cell voltage or the working current in the loop 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) , That is, close the battery discharge or charging circuit to ensure the safety of the user and the battery.

The working principle diagram of the protection board:

As shown in the picture, the IC is powered by a battery, and the voltage is between 2v and 5v to ensure reliable operation.

1. Overcharge protection and overcharge protection recovery

When the battery is charged and the voltage exceeds the set value VC (4.25-4.35V, the specific overcharge protection voltage depends on the IC), VD1 flips to make Cout low, T1 ends, and charging stops. When the battery voltage drops to VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on the IC), when Cout becomes high, T1 is turned on and charging continues, VCR must be a fixed value less than VC to prevent frequent jumps.

2. Over-discharge protection and over-discharge protection recovery

When the battery voltage drops to the set value VD (2.3-2.5V, the specific overcharge protection voltage depends on the IC) due to discharge, VD2 reverses, after a short time delay, Dout becomes low level and T2 ends. Discharge stops. When the battery is placed in charge, the internal OR gate is flipped to make T2 turn on again to prepare for the next discharge.

3. Over current and short circuit protection

When the charging and discharging loop current of the circuit exceeds the set value or is short-circuited, the short-circuit detection circuit acts to turn off the MOS tube and the current is cut off.