li ion charger circuit - Li-Ion Battery Charger Circuit Using IC LP2951

Li-Ion Battery Charger Circuit Using IC LP2951

The following post explains a very simple yet safe Li-Ion battery charger circuit using just a single IC LP2951.

Difference between Lead Acid and Li-Ion Battery

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.

How the Circuit Works

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 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 shown resistor values are precisely selected such that the IC generates an exact 4.2V at its output where the cell is connected.

The trimmer is added for refining the voltage in case there's any discrepancy with the resistor tolerance and ratings.

Initially when the particular discharged cell has a voltage level that's below the 4.2V, the IC  generates maximum current to the cell which is around 160mA as discussed above.

This initial current uplift charges the cell rapidly so that it attains the full charge rated value of 4.2V at an earliest.

Once the terminal voltage of the Li-Ion cell reaches the 4.2V mark, the IC LP2951 instantly inhibits the current so that the battery can longer exceed the 4.2 V level.

The above process highlights the ICs constant voltage regulation capability during the charging cycle.

The big value resistors included in the circuit ensures the "OFF" current drain of the battery to below 2mA, the 330pF capacitor stabilizes the circuit from unwanted noises created at the high-impedance feedback node.

The diode at the output is obviously for preventing the back flow of the battery voltage into the IC in the absence of input voltage.

courtesy -

Li-Ion Battery Charger Circuit Using IC LP2951


33 thoughts on “Li-Ion Battery Charger Circuit Using IC LP2951

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Nice Shearing,

    Meanwhile I'm looking for Li-Ion battery charter which can be charge 3 or 4 Cell together. Please share if you have anything like this.

    Thanks / Regards

  3. Hi sir i m from Pakistan.
    I have rechargeable cell who used in laptop battery.
    I want to use them in portable mobile charger. Who charge all cell phone like iphone htc lg samsung etc.
    Please suggest a simplest circuit for this purpose. Circuit must be run by 7.5 volts and made without ic 7805 or any else, because it produce too much heat.

    • Hi,

      7805 is simplest option, otherwise you will have to incorporate complicated SMPS design.

      A PWM circuit can be used but it will require precise adjustments, which might look difficult for a newbie

  4. Do you have a circuit for 3.7v Li-ion battery charger using a solar panel, or can I use this circuit to use a solar panel (what v and amp) as a 6v power supply? Since it is a tricle charger, maybe 4 hours sunlight is not enough to fully charge the battery? And there should be some regulator to cut off the overcharge the battery as Li-ion is more finiky than Ni-mah, isn't it? Need help please, thank you.

  5. If I couldnt model the li-ion phone battery charging circuit using the LM3622 as I couldnt find the model on pspice, I will try this one… Is it tested on pspice?

    • again, it's referred from a reputed manufacturers datasheet, stimulative testing may not be required.

      yes you can use it with a NOKiA phone. it should charge the battery within a couple of hours.

  6. Hi Sir,

    I bought a solar panel phone battery charger, I want to use the circuit inside and charge the cellphone battery from another external source (magnet moving inside a coil) it will produce an equivalent input voltage (around 5.5) will that work? and please if you have a circuit that charges a cellphone battery from a solar panel can you provide me with a link.

    many thanks

  7. Hi swagatam Sir,

    I am very new in electronic field started just 2 months back as a hobby of course. Getting inspiration from my wife she has a diploma in electronics ( i am a diploma in mechanical engg. so not much knowledge about electronics). We have just finished our IR Remote switch project which was posted in your blog .
    Now We are looking for a safe charger with auto cut off facility. So can you suggest some changes in this circuit for auto cut off facility
    And 2nd one can we use AC source with 9 volt transformer safely in this circuit

    Waiting for your reply eagerly. Thanks in advance

    • DearDinesh,

      Connect in this way:

      IN———>I———^^^^——–OUT, this will be off when charging.

      OUT———>I———^^^^——–Ground, this will ON when charging.

      The shown resistors can be 10k 1/4 watt.

  8. Hi there,

    btw, this is a great sharing and i appreciate it very much.
    this circuit construction is similar to my project and i wonder how do get to each of the values shown in the circuit so that i could made few adjustments to mine as per requirement.

    really appreciate if you could help here. tqvm!

    • Hi thanks!,

      The shown circuit above has an in-built current limiter which will not allow more than 160mA for the battery so this cannot be changed, as far as the voltage is concerned it may be changed to different levels by varying the attached pot.

      You may refer to the given link of the original datasheet for getting more info regarding the same and for other customized variations.

    • thank you for your reply..

      currently im doing the simulation for the circuit using LT spice. By any chance do you know how to model the li-on battery in the software so that i can obtain the charging and discharging characteristic of the battery?

  9. Hello , Dear Swagatam,
    I'm Hamza from Lebanon, i'm an electronics hobbyist , I would like to know if you have a circuit design that equalize the charging of lithium ion batteries connected in series so that none of them reaches a voltage above 4.2 v while the other cells are still charging, and also a circuit design that also equalizes the draw from these bateries so that the voltage across them stays close while discharging
    Thank you, Regards

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