Basic knowledge of battery protection board
The lithium battery protection board is a protection for the charging and discharging of the series lithium battery pack; when fully charged, it can ensure that the voltage difference between the individual cells is less than the set value (generally ±20mV), and realize the equal charge of the individual cells of the battery pack , Which effectively improves the charging effect in the series charging mode; at the same time, it detects the overvoltage, undervoltage, overcurrent, short circuit, and overtemperature status of each single cell in the battery pack to protect and extend the battery life; undervoltage protection makes every A single-cell battery is used to prevent damage to the battery due to over-discharge.
The finished lithium battery consists of two main parts, lithium battery core and protective plate. The lithium battery core is mainly composed of positive plate, diaphragm, negative plate and electrolyte; positive plate, diaphragm, negative plate are wound or laminated, packaged, and filled with electrolyte , The battery cell is made after packaging. Many people don’t know the role of the lithium battery protection board BMS. The battery management system, as the name suggests, is used to protect the lithium battery. The lithium battery protection board protects the battery Flow, there is output short-circuit protection.
Lithium battery protection board composition
Control ic, 2. Switch tube, plus some microcapacitors and microresistances. The function of controlling ic is to protect the battery. If the protection condition is reached, the mos is controlled to open or close (for example, the battery reaches the protection conditions of overcharge, overdischarge, short circuit, overcurrent, etc.), and the function of the mos tube is the switching function. It is controlled by the control ic.
The reason why lithium battery (rechargeable type) 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, which can accurately monitor the voltage of the battery cell and the current of the charging and discharging circuit under the environment of -40°C to +85°C.
The working principle of the protection board
1. Overcharge protection and overcharge protection recovery
When the 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 go to low level, T1 ends, and charging stops. When the battery voltage drops to VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on the IC), when Cout becomes high, 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 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.