The need for protection for rechargeable lithium-ion batteries stems from their inherent characteristics. Because the materials used in lithium-ion batteries dictate that they cannot be overcharged, over-discharged, over-currented, short-circuited, or charged and discharged at excessively high temperatures, lithium battery components are always accompanied by a sophisticated protection board and a current fuse.
The protection function of lithium-ion batteries is usually accomplished by the protection circuit board and current devices such as PTC. The protection circuit board is composed of electronic circuits that accurately monitors the voltage of the cell and the current of the charging and discharging circuit at all times in an environment ranging from -40℃ to +85℃, and controls the opening and closing of the current circuit in a timely manner. The PTC prevents the battery from being severely damaged in high-temperature environments.
The purpose of a power lithium-ion battery protection board is to protect the battery from damage caused by overcharging, over-discharging, and high current, and to perform battery voltage equalization when fully charged. To protect the lifespan of the lithium-ion battery pack, it is recommended that the battery charging voltage never exceed 3.6V, meaning the protection voltage of the lithium-ion battery protection board should not exceed 3.6V. The equalization voltage is recommended to be 3.4V-3.5V, and the battery discharge protection voltage is generally above 2.5V.
When the battery cell discharges through an external load, the battery cell voltage will gradually decrease. At the same time, the DW01 will monitor the battery cell voltage in real time through resistor R1. When the battery cell voltage drops to about 2.3V, the DW01 will consider that the battery cell voltage is in an over-discharge voltage state and immediately disconnect the output voltage of pin 1, making the voltage of pin 1 0V. The switching transistor in the 8205A will turn off because there is no voltage at pin 5.
At this time, the connection between the B- pin of the battery cell and the P- pin of the protection board is disconnected. That is, the discharge circuit of the battery cell is cut off, and the battery cell will stop discharging. The protection board remains in an over-discharge state.
