# Li-Ion Battery Charging using current controller

For a single Li-Ion battery cell charging process, one needs to do a CCCV cycle, in which first the li ion cell is charged using a constant current (of rating 1C normally), and when a specified voltage (4.2V) is reached, the battery is charged in a CV constant voltage cycle where the battery of the voltage is kept constant until the charging current falls to a specified value (normally 0.1C).

If i am charging my battery cell using a buck converter (a buck converter taking a PWM input from a micro-controller which is continuously monitoring battery's currnet, voltage and temperature), and i have designed a current controller for my buck converter to charge the battery, i will force some amount of current into the battery cell during the CC cycle by varying the duty cycle of the PWM (the amount of current would be increased and decreased by varying increasing and decreasing the duty cycle of my PWM respectively). When the battery cell Voltage reaches 4.2V, i have to now apply CV cycle to continue the charging process.

My question is regarding this Constant Voltage cycle. And the question is that would i apply the constant voltage cycle the same way i was applying the CC cycle? except now i would consider the battery voltage to be controlled, and against it i would be decreasing my PWM duty cycle in a way that the this voltage remains constant, and as a result of decreasing my PWM cycle my charging current would be continuously decreasing until it reaches a pont where i stop the charging. Am i right ? I mean to ask if the current control method would be enough for both the CC and CV method ? Which means ultimately in the CV cycle also, i would be controlling the current by decreasing it continuously, in such a way that my battery cell voltage doesnt go above 4.2V, am i right about it ?

Thankyou!

• Do you have some sort of over-voltage protection? I just imagined your software failing, PWM is still on and the battery explodes (literally). Oct 8, 2015 at 15:15
• Proposed method is fine as long as you do what you say. See answer below for more comment. As @Arsenal says - be sure your software never allows bad results worsst case. If batteries are valuable a separate hardware emergency overvoltage detector / alarm / shutdown is easy and cheap and may be worth doing. Oct 9, 2015 at 9:00