Lithium-ion Battery Charging Battery Solution
1 Overview of lithium ion battery and USB interface
Lithium ion (Li-ion) battery, referred to as lithium battery <http://bbs.dianyuan.com/tech/battery>, is gradually popular in recent years, the use of a new type of battery, with small size, light weight, large capacity ( High energy density), low self-discharge and no memory effect, but at the same time it also has some fatal flaws: the charging, discharge requirements are harsh, can not overcharge and over discharge, or likely to cause irreversible damage, Short circuit, overcharge and other extreme cases may also explode, dangerous.Battery Solution
General lithium battery single standard voltage of 316 ~ 317V, charging, the general requirements of the use of limiting current limit method, the first constant current charge, the current must be charged current according to national standards for low magnification charge is 0.2C (arbitration charge The maximum voltage of not more than 1C; and the battery voltage with the charging process gradually increased, when the battery voltage reaches the termination voltage of 412 ± 0105V, the constant current charge should be constant current (about 011C) charge, this state is generally Called trickle charge state. The charging current is reduced gradually to 0101C as the charging process continues to decrease according to the degree of saturation of the batteries.Battery Solution
USB interface Chinese meaning is "universal serial bus." It is a new application in the field of PC interface technology. USB uses a 4-pin plug as a standard plug to connect to an external device. In this 4-pin plug, there are two pins for the data communication line, while the outside of the two pins for the external device to provide power. In accordance with the USB specification, each USB interface should be able to provide 500mA of current output; USB host or powered by the hub to provide the USB interface, connected to the external terminal of the minimum available voltage of 4.5V, driven by the USB bus hub can provide Of the minimum should be 4.35 V. It is worth noting that although the USB specification defines the maximum current limit of not more than 015A, but in fact the USB port output current is often more than a few amps.
From the above analysis can be seen, the use of USB interface for lithium battery charging, the current should be sufficient, the key is how to control the size of the current. In addition, the use of a minimum voltage of 4.35V USB interface to the typical requirements of 4.2V lithium battery charging, the voltage is only a small margin, which makes the charge circuit voltage drop becomes extremely important, is the design of the difficulties.
2, based on the PC USB interface charging circuit design
Some of the "USB charging lines" on the market are internal circuits. The main principle is to use the resistance limit the maximum current, the use of diode voltage drop (about 0.7V) USB interface 5V output voltage down to about 4.2V and then charge the lithium battery. This circuit has the advantages of simplicity and low cost, but the drawback is obvious: the charging current and the charging voltage vary depending on the USB interface and the battery state, basically can not grasp, in many cases the battery is likely to be filled (Charging voltage of less than 4.2V), and sometimes it may overcharge and damage the battery. This circuit for some of the internal protection circuit with a perfect lithium battery is acceptable, and the ordinary lithium battery is a certain risk.Battery Solution