14: Protection circuit Part 2

Stopping discharging during over discharging

When the voltage of the lithium-ion battery becomes lower than a certain level, the coating base material of the negative electrode becomes ions, and ions in an electrolyte solution precipitate.
Precipitation on the positive electrode will affect capacity reduction and can cause the function of the positive electrode to decrease.

In addition, when ions are eluted in an electrolyte solution, iron is more likely to be ionized than copper (ionization tendency is large), so copper precipitates as a metal and iron elutes into an electrolyte solution as ions, and it can cause melting of a can and make a hole.
If the over discharged battery is left, holes will be made in the battery and an electrolyte solution will come out.

Since an electrolyte solution is conductive and combustible, there is a risk of electrolyte being ignited if it is charged while it is attached to a printed circuit board and so on.
Even boards that conform to safety standards may burn.
It is necessary to make sure that it does not fall below the voltage where serious cell deterioration occurs.

However, as can be seen from the discharge characteristic curve, the voltage suddenly drops from 3V or less.
Especially when discharging below around 2.3V, voltage drop occurs in a short time.
For this reason, the function to monitor the voltage of each cell and stop discharging below the set voltage is necessary.

Since the protection circuit can normally charge even in the over discharge protection state, it is necessary to set the voltage of the lithium-ion battery above the set voltage in order to release the protection state.

Caution must be taken because the method of release is different depending on the IC type of the protection circuit.

However, as there are some problems with the batteries with over discharge protection state, we recommend a method to release by charging instead of automatically releasing through voltage recovery.

A slight delay is set for over discharge protection operation, but it is not as common as overcharge protection.

<<Back

Next>>

Back to Index>>