Analyze the design of online charging and discharging management circuit for lithium batteries

Design of online charge and discharge management circuit for lithium batteries 1 Characteristics of lithium batteries In recent years, the rapid development of portable electronic products has led to the upgrading of battery technology. During the period, lithium batteries continued to emerge with the characteristics of high energy density, high internal resistance, high battery voltage, high cycle times, and low self-discharge rate, and became the mainstream of the market. According to statistics, in the field of notebook computers and mobile phones, the market share of lithium batteries is 80% and 60% respectively. According to Japan’s Yano Institute of Economic Research, lithium batteries are rapidly replacing traditional nickel-chromium and nickel-metal hydride batteries with an annual increase rate of 53.33%. Although the lithium battery has the above advantages and a good future direction, it is a relatively high circuit maintenance requirement. During the application process, the phenomenon of excessively high charges should be strictly prevented. Overdischarge and discharge current should not be too large. Generally, Said that the discharge rate should not exceed 0.2c. The charging process of the lithium battery is shown in Figure 1. During the charging cycle, the voltage and temperature of the lithium battery must be tested before charging to determine whether it can be charged. If the battery voltage or temperature exceeds the manufacturer's permitted schedule, charging is prohibited. Allowable charging voltage planning is: 2.5v~4.2v per battery; temperature method: 2.5℃~50℃. When the battery is in a deep discharge state, the charger must be pre-charged so that the battery can meet the conditions for fast charging; then, according to the fast charging speed recommended by the battery manufacturer, generally 1C, the charger is charged at a constant current, and the battery voltage is slow rise. When the battery voltage reaches the set intermittent voltage (generally 4.1v or 4.2v), the constant current charging is interrupted, the charging current decays rapidly, and the charging enters the full charging process. In the process of fully charging, the charging current gradually decays until the charging rate drops below C/10 or the charging time is over, then turn to the top to stop charging. When charging at the top, the charger uses very little charging current to supplement the battery's energy. After charging at the top for a while, turn off charging. Generally speaking, the lower limit of the safety voltage of lithium batteries is 2.4v, and the charging voltage required by the error accuracy is not accurate, but it must be equipped with an appropriate over-discharge delay time in order to coordinate the maximum load of the power and the maintenance requirements of over-discharge. When the battery is discharging, and the battery voltage is lower than the over-discharge sustaining voltage, the battery discharge should be turned off to prevent the occurrence of battery over-discharge. When the discharge current is too large, the maintenance circuit should close the battery to discharge, showing the over-discharge current maintenance function. The size of the maintenance current can be set according to the size of the load. It is worth noting that the maintenance circuit cannot malfunction due to the short-period high current load demand. The maintenance circuit must provide different over-discharge current maintenance delay times to improve the stability of operation. In addition, the maintenance function of all lithium battery packs can also perform internal pressure maintenance through the safety threshold of the battery, and high temperature maintenance through the thermistor of the external circuit. 2. On-line charging and discharging processing circuit structure As the maintenance circuit requirements of lithium batteries are relatively high, when planning the charging and discharging circuit, various possible situations should be fully considered and maintenance should be carried out to ensure the safe operation of the battery. In the actual planning, the lithium battery should be used in unattended musical instruments for a long time, and the charging and discharging circuit should actively monitor the conditions of the lithium battery, external power supply and load, and make corresponding actions to ensure the load for a long period of time. Stable operation of time and safe and effective operation of lithium battery. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Are lead-acid batteries and UPS lithium batteries charged in the same way?