First, let the lithium battery drop to 3.3V through the step-down chip, then supply power to the microcontroller and Bluetooth module, and plan to rise to 7V to carry a load.

　　Result: The Bluetooth module does not work and cannot be searched. With Bluetooth removed, the MCU and the load work normally. When the microcontroller is removed, Bluetooth and the load work normally. When a group of power supplies are separately supplied without voltage reduction, all three will work normally.

　　Note: xc6206 for step-down and fd6291 for step-up.

　　2. Voltage rise and drop of lithium battery

　　Next, we will analyze the causes of the above problems, find out the common problems of the pressure rise and fall of the lithium pool, and learn together.

　　The single voltage of lithium ion battery has a certain range, for example, the normal working voltage range of lithium iron phosphate battery is 2.5V-3.65V, and the normal working voltage range of lithium manganate and ternary battery is 3V-4.2V.

　　In the application of lithium ion battery, when the total voltage is 60V or below, the battery protection board is required. Above 60V, the battery management system (BMS) is required. The function of these two devices is to protect the battery.

　　Note that the voltage of the battery pack cannot be adjusted at will after the number of strings of the battery pack is determined. That is, the voltage change of the battery pack can only be changed within the normal working voltage range: when charging, it rises from the lower voltage limit to the upper voltage limit. When power is used, it drops from the upper voltage limit to the lower voltage limit.

　　I understand this problem. If you want to increase or decrease the pressure range of lithium battery, you can adjust it at will.

　　The best solution: a set of batteries, a suitable inverter, and a DC voltage regulator can meet the pressure rise and drop requirements of lithium batteries.

　　Note: This method is rarely used in practical applications. Unless the AC power supply used is often cut off, or the solar or wind energy is used to charge the battery pack, this method of boosting and reducing voltage will be considered.

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