Charger to the phone charging in two ways: cradle and direct charge. Cradle is to remove the lithium-ion battery charger in the charge, with the corresponding direct charge, that is, the charger directly connected to the phone charging. USB charging refers to the use of USB interface, electrical equipment, mobile phone charging, the current special PC and notebook computers. Usually, USB charging charge time than the charger to be much longer, in order to explain the difference between USB charging and DC charging, first understand the principle of lithium battery charging.
(1), pre-charge, this time the voltage is less than 3V; (2), constant current charging, the voltage reaches 3V, into the fast charging stage, this is the charge of the lithium battery is limited to constant current, generally after three charging stage: (3), constant voltage charging, when the voltage rose to 4.2V, the small current charge, and the voltage of 4.2V unchanged. The current is constant, the constant current charge continues to voltage up to 4.2V; Typically, the current at this time is 1/10 of the constant current stage.
Cradle and direct charge method will be on the lithium battery and mobile phone caused a certain impact, long-term will form a certain degree of damage. And the USB output current is smaller than the above two, which is the USB charging time longer than the two reasons, this small current performance in the constant current and constant voltage stage. The purpose of constant voltage charging is to add lithium-ion battery after full charge due to self-discharge caused by the loss of capacity.
At present, the computer's USB output voltage is 5V, the output current is 500mA, and the charger charging current is 1000mA. Because the USB output current is small, its current in the constant voltage stage is even smaller.
Therefore, with USB charging feel longer, which is more important is spent in the constant pressure stage of a long time. If you can not wait and put the USB to the phone charging the end of the process, because there is still part of the supplementary charge did not charge into it, it seems a bit full of full look. This is actually the current problem rather than consumers worry about leakage and so on other issues. However, the "full" problem is not affected, even if there is no constant voltage charging process, this time the battery at least 90% of the capacity, for lithium batteries, as long as the charge and over discharge, ready to charge , Which is the difference between it and nickel-metal hydride batteries.