How to protect rechargeable batteries

April 14, 2021

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Over current and short-circuit current

For unknown reason (or discharge is the cathode metal by accident) cause over current or short circuit, in order to ensure safety, must immediately stop discharge.

For over current protection IC principle, when the discharge current is too large, or short circuit occurs, protection IC will activate a short circuit current protection, over current at this time of testing is to power MOSFET Rds (on) as inductive impedance to monitor its voltage drop, if is higher than set by the over-current detection voltage is stop discharging, in the same way, over-current detection must also be equipped with delay time in case when the breaking current is flowing into produce false action.

Usually after the over current to produce, if can remove overcurrent factors (e.g., immediately and load out), will return to its normal state, charge and discharge can be normal again.


Overcharge protection

Overcharge protection IC principle is: when the external charger for lithium battery, in order to prevent due to temperature rise caused by internal pressure rise, need to terminate the charging status. At this point, the protection of IC to detect the battery voltage, when arrived at 4.25 V (assuming the battery overcharge point of 4.25 V) that activate the overcharge protection, cutting the power MOSFET from open to, and stop charging.

In addition, you must pay attention to because of the noise generated by the excessive charging detection misoperation, lest judge for protection. Therefore, we need to set the delay time and delay time can not be shorter than the duration of the noise.