Lithium battery protection circuit -Lithium - Ion Battery Equipment

The principle of lithium battery protection circuit -Lithium - Ion Battery Equipment

The principle of lithium-ion battery protection circuit

The reason why the lithium-ion battery (rechargeable) needs to be protected is determined by its own characteristics. Since the material of the lithium-ion battery itself determines that it cannot be overcharged, overdischarged, overcurrent, short-circuited and ultra-high temperature charge and discharge, the lithium-ion battery components will always appear with a delicate protection board and a current fuse. The protection function of lithium-ion batteries is usually completed by the protection circuit board and current devices such as PTC. The protection board is composed of electronic circuits, which can accurately monitor the voltage of the battery cells and the charging and discharging circuit at all times in the environment of -40°C to +85°C. The current can be controlled in time, and the on-off of the current loop can be controlled in time; the PTC can prevent the battery from being badly damaged in a high temperature environment.(Lithium - Ion Battery Equipment)

Ordinary lithium-ion battery protection boards usually include control ICs, MOS switches, resistors, capacitors and auxiliary devices FUSE, PTC, NTC, ID, memory, etc. Among them, the control IC controls the MOS switch to turn on when everything is normal, so that the cell is connected to the external circuit, and when the cell voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off to protect the battery cell. Safety.

1. Lithium-ion battery charging

The maximum charge termination voltage of a single-cell lithium-ion battery is 4.2V, and it cannot be overcharged, otherwise the battery will be scrapped due to the loss of too much lithium ions in the positive electrode. When charging the lithium-ion battery, a dedicated constant-current and constant-voltage charger should be used. First, the constant-current charge until the voltage at both ends of the lithium-ion battery is 4.2V, and then switch to the constant-voltage charging mode; when the constant-voltage charging current drops to 100mA should stop charging.

The charging current (mA) can be 0.1 to 1.5 times the battery capacity. For example, for a 1350mAh lithium-ion battery, the charging current can be controlled between 135mA and 2025mA. The conventional charging current can be selected at about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours.

2. Discharge of lithium-ion batteries

Due to the internal structure of the lithium-ion battery, the lithium ions cannot all move to the positive electrode during discharge, and a part of the lithium ions must be retained at the negative electrode to ensure that the lithium ions can be smoothly inserted into the channel during the next charging. Otherwise, battery life will be shortened. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to strictly limit the minimum discharge termination voltage, that is to say, the lithium ion battery cannot be overdischarged.

The discharge termination voltage of a single-cell lithium-ion battery is usually 3.0V, and the minimum cannot be lower than 2.5V. The length of battery discharge time is related to battery capacity and discharge current. Battery discharge time (hours) = battery capacity/discharge current, and the lithium-ion battery discharge current (mA) should not exceed 3 times the battery capacity, for example: 1000mAh lithium-ion battery, the discharge current should be strictly controlled within 3A, otherwise will damage the battery.



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