simple Li-Ion Battery Charger Circuit Using IC LP2951

How to make a simple Li-Ion Battery Charger Circuit Using IC LP2951

By : Alok kumar

Today's post explains a very simple yet safe Li-Ion battery charger circuit using just a single IC LP2951. Unlike lead acid batteries the one good thing about the Li-Ion batteries is that they can be charged at 1C rate (simply fast charging) initially. It means the battery's charging current can be as high as the rated AH (Ampere*Hour) of the li-ion battery at the onset. The design presented in this post 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 above diagram depicts a configuration which was used for charging a Li-Ion battery of a portable stereo unit. The charging specification of the circuit us as under:

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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 is the only main active component which has been specifically chosen because it is capable of delivering an output voltage that is very stable over temperature variation.

The device also features an in-built current regulation system which limits the output from producing current above the 160mA mark.

Furthermore the IC is entirely short circuit proof and incorporates a thermal shut down facility.

The resistor values are precisely selected such that the IC generates an exact 4.2V at its output where the cellphon battery is connected.The trimmer is added for refining the voltage in case if any discrepancy with the resistor tolerance and ratings.Initially when the particular discharged cell phon battery has a voltage level that is below the 4.2V, the IC generates maximum current to the cell phon battery which is around 160mA. This initial current uplift charges the cell phon battery rapidly so that it attains the full charge rated value of 4.2V at an earliest.

Once the terminal voltage of the Li-Ion battery reaches the 4.2V mark, the IC LP2951 instantly restricts the current so that the battery can longer exceed the 4.2 V level. The above process highlights the IC's constant voltage regulation capability during the charging cycle of the li-ion battery.

The high value resistors included in the circuit ensures the "OFF" current drain of the battery to below 2mA, here the 330pF capacitor stabilizes the circuit from unwanted noises produced at the high-impedance feedback node. Here the diode across the output is for preventing the back flow of the battery current into the IC in the absence of input voltage.

For any further querrys please comment in below the comment section. Thank you for reading.