The working principle and process of lithium battery protection board

by:CTECHi     2021-07-16

The finished lithium battery consists of two main parts, the lithium battery core and the protection board. Many people don't know the role of lithium battery protection board. Lithium battery protection board, as the name suggests, is used to protect lithium batteries. The role of lithium battery protection board is to protect the battery from over-discharge, over-charge, over-current, and output short-circuit protection.

The circuit and parameters of the lithium battery protection board are different according to the IC, voltage, etc., and the commonly used protection ICs are 8261, DW01+, CS213, GEM5018, etc., among which Seiko’s The 8261 series has better accuracy, and of course the price is more expensive. The latter are all made in Taiwan, and DW01+ and CS213 are basically used in the domestic secondary market. The working process of the lithium battery protection board can be divided into the following points:

The working principle diagram of the lithium battery protection board

1. The method of activating the protection board: When the protection board P+ and P- are not in the protection state, you can short-circuit B- and P- to activate the protection board. At this time, Dout and Cout will be in low level (the two ports of the protection IC are high level protection, low power Normal state) state to open two MOS switches.

2. Charging: P+ and P- are respectively connected to the positive and negative poles of the charger, and the charging current passes through two MOSs to charge the cell. At this time, the VDD and VSS of the IC are both the power supply and the power supply. Core voltage detection terminal (via R1). As the charging progresses, the cell voltage gradually increases. When it reaches the protection IC threshold voltage (usually 4.30V, usually referred to as the overcharge protection voltage), Cout will immediately output a high level to turn off the corresponding MOS. The charging circuit is also disconnected. After the overcharge protection, the cell voltage will drop. When it drops to the IC threshold voltage (usually 4.10V, usually called the overcharge protection recovery voltage), Cout returns to a low level and opens the MOS switch .

3. Discharge: Similarly, when the battery is discharged, the VDD and VSS of the IC will also detect the cell voltage. When the cell voltage drops to the IC threshold voltage (usually 2.40V, usually called over Discharge protection voltage), Dout will immediately output high level corresponding to that MOS is turned off, and the discharge circuit is disconnected. After over-discharge protection, the cell voltage will rise, when it rises to the IC threshold voltage (usually 3.00V, usually called When the voltage is restored for over-discharge protection), Dout returns to a low-level state to open the MOS switch.

4. Overcurrent, short circuit: When the main circuit current is large during the discharge process (refer to the design parameters of the protection board for details), because the MOS saturation conduction also has internal resistance, the current is flowing through B -, between P-, there will be a voltage drop at both ends of the MOS. V- and VSS (through R2) of the protection IC will detect the voltage at both ends of the MOS at any time. When the voltage rises to the IC protection threshold (usually 0.15V, called discharge) Over-current detection voltage), Dout will immediately output a high level and the corresponding MOS will be turned off, and the discharge circuit will be disconnected.

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