CR2032 button cell.Implementing battery chargers using lithium-ion technology

　　The use of lithium-ion technology to implement a battery charger is provided to you by electronic enthusiasts. In this article, we will give an example of how to use lithium-ion technology to implement a battery charger. Lithium-ion battery chargers usually use a constant current (CC) - constant voltage (CV) charging curve. The charging process will go through several different stages to ensure that the battery capacity is full

　　In this article, we will provide an example of how to implement a battery charger using lithium-ion technology. Lithium-ion battery chargers usually use a constant current (CC) constant voltage (CV) charging curve. The charging process goes through several different stages, ensuring the battery is fully charged while complying with specific safety rules. The CC-CV curve includes the following stages:

　　1.Precharge

　　2.Activate

　　3.Constant current

　　4.Constant voltage

　　Charging begins with a pre-charge phase to check whether the battery is in good condition. In this stage, a small amount of current of 5% to 15% of the battery capacity is usually provided to the battery. If the battery voltage rises above 2.8V, the battery is considered to be in good condition and can enter the activation stage. During this phase, the same current is supplied to the battery, but for a longer period of time. When the battery voltage rises above 3V, fast charging is started and a constant current equal to or lower than the battery capacity is provided. The constant current phase ends when the battery voltage rises to the full charge voltage (4.2V) or when a timeout occurs (whichever occurs first). When the battery voltage reaches the full charging voltage, charging enters the constant voltage stage and the battery voltage remains constant. To do this, the charging current must decrease over time. The charging process at this stage takes the longest time compared to other charging stages. During this process, when the charging current drops below the "end current" limit, usually 2% of the battery capacity, the battery is fully charged and the charging process ends. Please note that each stage of the charging process has a time limit, which is an important safety feature.

　　In order to implement this charging profile, the battery voltage and charging current must be known at all times. Also, check the temperature of the battery. Because batteries tend to get hot when charging. If the temperature exceeds the specified limit of the battery, it may cause damage to the battery.

　　In terms of battery charger implementation, users have two options. One is to use a specialized battery charger IC, and the other is to use a more general microcontroller. The first solution solves the problem quickly, but has limited configurability and user interface options (LED indicators). The second option uses a microcontroller, which takes slightly longer to design, but provides configurability options and can integrate other functions, such as battery state of charge (SOC) calculation and communication interface to the host in the system. The device sends information, etc. In addition, the microcontroller cannot provide the power circuitry necessary for the charger, and an external BJT or MOSFET is required. However, the cost of these power components is much lower than that of microcontrollers or specialized charger ICs.

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