Lithium battery overprotection principle, the working principle of lithium battery protection board. The safety of lithium-ion battery-powered equipment is currently the most important concern, so its protection is very important. Lithium battery protection plate can protect the lithium battery to prevent overcharge, over discharge or short circuit caused by the high current discharge.
Lithium battery overprotection principle
Lithium-ion battery protection circuit is composed of a protection IC and two power MOSFETs, where the protection IC monitors the battery voltage, when there is an overcharge and discharge state to switch to the external power MOSFET to protect the battery, the function of the protection IC overcharge protection, overdischarge protection and overcurrent / short circuit protection.
I. Overcharge protection
The principle of the overcharge protection IC is: when the external charger is charging the lithium battery, in order to prevent the rise in internal pressure caused by the temperature rise, the charging state needs to be terminated. At this time, the protection IC needs to detect the battery voltage, when it reaches 4.25V (assuming that the battery overcharge point is 4.25V) is activated overcharge protection, the power MOSFET from open to cut off, and then cut off the charge.
In addition, attention must be paid to overcharge detection malfunctions due to noise, so that overcharge protection is not determined. Therefore, a delay time needs to be set, and the delay time cannot be shorter than the duration of the noise.
II. Over-discharge protection
In the case of over-discharge, the electrolyte decomposes and leads to the deterioration of the Li-ion battery characteristics and the reduction of the charging times. The use of lithium battery protection IC can avoid the phenomenon of over-discharge and realize the battery protection function.
Over-discharge protection IC principle: In order to prevent the over-discharge state of the lithium battery, assuming that the lithium battery is connected to the load, when the lithium battery voltage is lower than its over-discharge voltage detection point (assumed to be 2.3V) will activate the over-discharge protection, so that the power MOSFET from open to cut off and cut off the discharge, in order to avoid the over-discharge phenomenon of the lithium battery, and keep the battery in a low quiescent current standby mode. At this time, the current is only 0.1μA.
The working principle of lithium battery protection board
The principle of lithium battery protection board as a safety protection device for lithium battery cells, both in the normal operating current range of the device, can work reliably, but also when the battery is accidentally short-circuit or overcurrent can quickly act, so that the battery cells are protected. Under the normal condition of Li-ion battery protection board principle, Vdd is high level, Vss, VM is low level, DO, CO is high level, when Vdd, Vss, VM any one parameter change, DO or CO side level will change.
Lithium battery protection board according to the use of IC, voltage and other different circuits and parameters vary, the protection board has two core components: a protection IC, which is a precise comparator to obtain reliable protection parameters; the other is a MOSFET string in the main charge and discharge circuit as a high-speed switch, the implementation of the protection action.
We use the lithium battery is actually composed of several small internal lithium batteries connected in parallel in one piece. In the gap between the internal lithium battery has a few pieces of plastic like the plate will be separated from them. These small plastic-like plate is actually the lithium battery protection plate. In fact, the lithium battery protection plate is not made of plastic.
Lithium battery protection plate can protect the lithium battery why?
1. lithium-ion battery voltage to 4.2V, if you continue to charge, the positive structure will partially collapse, permanent loss of capacity, if you continue to charge, easy to produce dendrites, piercing the diaphragm, resulting in a short circuit of the positive and negative electrodes of the cell, which will lead to combustion and explosion;
2. Li-ion battery in the voltage as low as 2.4V, part of the material will be passively damaged, if continue to discharge, will cause both capacity loss, more will cause loss of life. General deep discharge to 2.75V will cut off, and 3V to 2.75V only 3%, so generally do 3V protection;
3. Li-ion is more active, if the temperature is too high, will greatly reduce the life of the battery;
4. The current will also have an impact on the battery cell, such as excessive current when discharging, the positive and negative electrode reaction timing chaos, easily lead to similar to the overcharge voltage, dendrites, resulting in scrap.
Based on the above four points, the protection board needs to do charge and discharge voltage protection, current protection, temperature protection, etc.; do the above points protection board can naturally produce protection for lithium batteries.
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