The working principle of the lithium battery protection board and the composition of the protection board
The working principle of the lithium battery protection board and the composition of the protection board. The lithium battery protection board can effectively prevent the lithium battery from overcharging, overdischarging and short circuit of the internal circuit. Secondly, we talked about the lithium battery protection board also has the function of protecting the battery and avoiding battery overcharging. When the external power supply continues to charge the battery quickly, the lithium battery protection board will have a protective effect. This is exactly the principle that the lithium battery protection board protects the battery from overcharging.
Working principle of lithium battery protection board
1. Overcharge protection and overcharge protection recovery
When the lithium battery is charged and the voltage exceeds the set value VC (4.25-4.35V, the specific overcharge protection voltage depends on the IC), VD1 flips to make Cout low, T1 ends, and charging stops. When the battery voltage drops to When VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on IC), Cout changes to high level, T1 is turned on and charging continues, VCR must be a fixed value less than VC to prevent frequent jumps.
2. Over-discharge protection and over-discharge protection recovery
When the lithium battery voltage drops to the set value VD (2.3-2.5V, the specific overcharge protection voltage depends on the IC) due to discharge, VD2 reverses, after a short time delay, Dout becomes low and T2 ends , Discharge stops, when the battery is placed in charge, the internal OR gate is flipped to make T2 turn on again to prepare for the next discharge.
3. Over current and short circuit protection
When the charging and discharging loop current of the circuit exceeds the set value or is short-circuited, the short-circuit detection circuit acts to turn off the MOS tube and the current is cut off.
Due to the chemical characteristics of lithium batteries, during normal use, the internal chemical positive reaction of the mutual conversion of electric energy and chemical energy, but under certain conditions, such as overcharging, overdischarging and overcurrent will cause the internal battery A chemical side reaction occurs. When the side reaction is intensified, it will seriously affect the performance and service life of the battery, and may produce a large amount of gas, which will cause the internal pressure of the battery to rapidly increase and then explode, causing safety problems. Therefore, all lithium batteries need a protection The circuit is used to effectively monitor the charging and discharging status of the battery, and to shut off the charging and discharging circuits under certain conditions to prevent damage to the battery.
Composition of lithium battery protection board
The reason why the lithium battery needs protection is determined by its own characteristics. Since the material of the lithium battery itself determines that it cannot be overcharged, overdischarged, overcurrent, short circuited, and ultra-high temperature charging and discharging, the lithium battery components of the lithium battery will always appear with a delicate protection board and a current fuse. The protection function of the lithium battery is usually completed by the protection circuit board and PTC. The protection board is composed of electronic circuits. It can accurately monitor the voltage of the battery cell and the current of the charging and discharging circuit under the environment of -40℃ to +85℃. Control the on and off of the current loop; PTC prevents severe damage to the battery in a high temperature environment.
The protection board usually includes control IC, MOS switch, resistor, capacitor and auxiliary device NTC, ID memory and so on. Among them, the control IC controls the MOS switch to turn on under all normal conditions, so that the battery cell communicates with the external circuit, and when the voltage or loop current of the lithium battery cell exceeds the specified value, it immediately controls the MOS switch to turn off (tens of milliseconds). Protect the safety of batteries.
NTC means negative temperature coefficient. When the ambient temperature rises, its resistance decreases, and the use of electrical equipment or charging equipment responds in time and controls internal interruptions to stop charging and discharging. ID memory is often a single-wire interface memory, ID is to store information such as battery type and production date. Can play a role in product traceability and application restrictions.
Lithium battery protection boards have different circuits and parameters depending on the IC, voltage, etc. used. The protection board has two core components: a protection IC, which uses a precise comparator to obtain reliable protection parameters; the other is a series of MOSFETs. Acting as a high-speed switch in the main charging and discharging circuit to perform protection actions.
When the lithium battery is over-discharged, the internal memory content of the lithium battery will undergo a qualitative change. At this time, the lithium battery protection board can sense this, so as to quickly cut off the discharge power supply so that the lithium battery will not discharge all the electricity. This ensures the stability of the internal current of the lithium battery and avoids the over-discharge of the lithium battery.