A question about LI-ION battery's charge phase

As we know,there are 3 phases of charging the Li-ion battery,
which is precharge,constant-current,constant-voltage.
I have some difficulty understanding the constant-voltage phase.

For example,if we want to charge 1 pack li-ion 4.2v battery, 500ma current is used in the constant-current phase,after the voltage of the battery rise to 4.2v,in the
constant-voltage phase,the voltage of the battery keeps 4.2v,the current decrease gradually from 500ma to the point that the battery can tape off.

My question is why the battery's voltage can keep constant when there is still
constant current charging the battery and if I want to design such a circuit,
what should I do to realize the constant-voltage phase.

ps:Attachment is the figure of 3 phase of Li- ion battery chargeing

newhand said:

My question is why the battery's voltage can keep constant when there is still
constant current charging the battery and if I want to design such a circuit,
what should I do to realize the constant-voltage phase.

Click to expand...

Hello newhand,

In the constant voltage phase the current isn’t constant. The charge controller is switching from constant current to constant current when the voltage reaches 4.2V (4.1V). The constant voltage can be achieved with a very simple voltage controller. But be aware of designing such a circuits by yourself. Li-Ion batteries are very sensitive in overvoltage (max +0.5%)! The easiest way and probably the cheapest way is to take a special charger IC (for example from Maxim, TI, …). There are a lot of these charger circuits on the market. If you define your requirements I think you will find the correct IC.

Bye,
cube007

thanks for your advice,cube007,^_^

Hello newhand,

You are new at this forum. Please don’t post only for thanking someone. Use the “Helped me bottom” () instead.


Bye,
cube007

i know its some kind of fast charge and slow charge, and the latter will consume very small current and the voltage will stable no change or will decrease

Allow me to add:

Could someone help me with some more information
about preconditioning phase?

thanks in advance!