DS

The following post explains a very simple yet safe Li-Ion battery charger circuit using just a single IC LP2951. Unlike lead acid batteries one good thing about the Li-Ion batteries is that they can be charged at 1C rate initially. It means the charging current may be as high as the rated AH of the battery at the onset. The design presented in this article can be used for charging a single 3.7V Li-ion cell or a standard cell phone battery externally at a relatively slower rate. The diagram depicts a configuration which was used for charging a Li-Ion cell of a portable stereo unit. The charging specification of the circuit may be summarized as under: Maximum charging current = 150mA Full charge volt = 4.2V +/- 0.025V Charge Current = set at current limit charge mode.    In the given circuit the IC LP2951 becomes the main active component which has been specifically chosen because it is capable of delivering an output voltage that's very stable over temperature. The...

The LP2951 regulator is manufactured by National Semiconductors. The choice of values is from an application note "Battery Charging", written by Chester Simpson. Diode D1 can be any diode from the 1N00x series, whichever is conveniently available. It functions as a blocking diode, to prevent a back flow of current from the battery into the LP2951 when the input voltage is disconnected. Charging current is about 100+mA, which is the internally-limited maximum current of the LP2951. For those wondering, this is compatible with just about any single-cell li-ion battery since li-ion can generally accept a charging current of up to about 1c (i.e. charging current in mA equivalent to their capacity in mAh, so a 1100mAh li-ion cell can be charged at up to 1100mA and so on). A lower charging current just brings about a correspondingly longer charge time. IMHO 100mA is quite low, low enough that the circuit can be used for an overnight charger for many typical single-cell li-ion batte...