no. 7 alkaline battery.The importance of lithium battery charging circuit and protection circuit design

　　The importance of lithium battery charging circuit and protection circuit design. In the design of circuits using lithium batteries as power sources, increasingly complex mixed-signal systems are required to be integrated into a small-area chip, which inevitably raises low-voltage and low-power consumption issues for digital and analog circuits. Therefore, the design of lithium battery charging circuit and protection circuit is very important.

　　The necessity of lithium battery protection circuit

　　Due to the high energy density of lithium batteries, in the overcharged state, the energy will be excess when the battery temperature rises, so the electrolyte decomposes to produce gas, which can easily increase the internal pressure and cause the risk of spontaneous combustion or rupture; conversely, in the overdischarged state, The decomposition of the electrolyte causes the battery characteristics and durability to deteriorate, reducing the number of recharges and shortening the battery life. Therefore, the protection of lithium batteries is very important. Lithium battery applications must have battery protection chips to prevent battery overcharge, overdischarge and overcurrent.

　　To sum up, the design of lithium battery protection circuit is very important. We require lithium battery power protection chips to be able to achieve the following most basic functions: overcharge protection, over-discharge protection, over-current protection and short-circuit protection. From the above application requirements of lithium batteries, it can be seen that in order to improve the service life of lithium batteries and ensure the safe use of batteries.

　　Lithium battery protection circuit needs to have the following functions

　　(1) If the charging voltage exceeds the maximum allowed value of the battery, a battery discharge circuit can be provided.

　　(2) If the discharge voltage is lower than the minimum allowed value of the battery, a battery charging circuit can be provided. The battery is disconnected from the external circuit, and the battery is disconnected from the external circuit.

　　(3) If the charge and discharge current of the lithium battery is greater than the limit value, cut off the connection between the battery and the external circuit.

　　(4) When the lithium battery returns to normal state, the protection circuit should be able to release the protection state accordingly so that the battery can continue to work normally.

　　Things to note when designing lithium battery circuits

　　▲Overcharging and over-discharging lithium batteries will affect the life of the battery.

　　▲Pay attention to the charging voltage and charging current of the lithium battery. Then choose the appropriate charging chip.

　　▲Be careful to prevent overcharging, over-discharging, short-circuit protection and other problems of lithium batteries.

　　▲After design, a lot of testing is required.

　　Design of lithium battery charging circuit management

　　When a lithium battery is charged, the potential applied to the two poles of the battery forces the compound in the positive electrode to release lithium ions and embed them in the carbon in which the negative electrode molecules are arranged in a lamellar structure. During discharge, lithium ions are precipitated from the carbon in the lamellar structure and recombine with the compound of the positive electrode. The movement of lithium ions creates an electric current. Although the principle is very simple, in actual industrial production, there are many more practical issues that need to be considered: the material of the positive electrode needs additives to maintain the activity of multiple charges and discharges, and the material of the negative electrode needs to be designed at the molecular structure level to accommodate more More lithium ions; the electrolyte filled between the positive and negative electrodes, in addition to maintaining stability, also needs to have good conductivity and reduce the internal resistance of the battery.

　　When the lithium battery is in deep discharge, the charger must be required to have a precharge process so that the battery can meet the conditions for fast charging; then, according to the fast charging speed recommended by the lithium battery manufacturer, which is generally 1C, the charger performs a constant charge on the battery. During constant current charging, the battery voltage rises slowly; once the battery voltage reaches the set termination voltage, constant current charging is terminated, the charging current rapidly decays, and charging enters the full charge process.

　　When we design products that require the use of lithium batteries, we need to design a protection circuit for the lithium battery. Only on this basis can we design the charging circuit. Lithium batteries require overvoltage charging protection, overvoltage discharge protection, overcurrent discharge protection, short circuit protection, etc. Therefore, when we design a lithium battery protection circuit, we must at least achieve the above protection functions.

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