Why does USB take too long to charge the mobile phone lithium-ion battery?

There are two ways for the charger to charge the mobile phone: cradle charging and direct charging. Dock charging is to remove the battery and charge it on the charger, which matches with the direct charge, that is, connect the charger to the mobile phone to charge immediately. USB charging refers to the use of electrical equipment with USB sockets to charge mobile phones. At this stage, it refers to PCs and laptops. Generally, USB charging takes much longer time than charger charging. In order to better show the difference between USB charging and DC charging, we must first grasp the basic principles of lithium-ion battery charging. The charging method of lithium ion battery is the current limiter constant current power supply, which generally goes through three charging links: (1), pre-charging, the working voltage is lower than 3V at this time; (2), constant current power charging, the working voltage is 3V Then, it enters the rapid charging link. At this time, the amount of current is large, and the constant current power supply continues to charge until the working voltage rises to 4.2V; (3) Constant current source charging, when the working voltage rises to 4.2V, change to low power Flow charging, while the working voltage of 4.2V will not change. Generally, the amount of current at this time is 1/10 of the constant current power supply link. Customized charging and direct charging methods for lithium-ion battery production will each cause a certain impact on lithium-ion batteries and mobile phones, and a certain level of harm will occur in the long-term. The USB output current is smaller than the above-mentioned two, which is why the USB charging time is longer than the two. This kind of small current meter is now a constant current power supply and a constant current source link. The purpose of constant current source charging is to compensate for the volume damage caused by the life of the lithium-ion battery after the lithium-ion battery is fully charged. At this stage, the USB output voltage on the computer is 9V, the output current is 1000mA, and the charger charging current is 100mA. Since the USB output current is small, the current in the constant current source link becomes even smaller. Therefore, it takes longer to charge with USB. Among them, the more important thing is the long time spent in the constant current source. If you can’t wait to complete the entire process of charging the phone with USB as soon as possible, it seems a bit unsatisfactory because there is still a part of the supplementary battery that has not been charged in. This is actually a current flow problem rather than other problems such as power failure that customers are worried about. 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: What is the difference between lithium ion battery and lithium iron phosphate battery