Balanced working principle of lithium iron phosphate battery protection chip and lithium battery protection board
Working principle of lithium iron battery protection chip
The lithium iron phosphate battery circuit has the functions of overcharge protection, overdischarge protection, overcurrent protection and short circuit protection. Only by understanding the working principles of these basic protection chips can we better design lithium iron phosphate battery packs, and even assist the quality part in analyzing abnormal batteries or circuits. The reason why the lithium iron phosphate 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 iron-lithium battery is usually completed by the protection circuit board and current devices such as PTC. The protection board is composed of electronic circuits, which can accurately monitor the voltage of the battery cell and the charging and discharging circuit under the environment of -40℃ to +85℃. It can control the on and off of the current loop in time; PTC prevents severe damage to the battery under high temperature environment.
1. Introduction to the main components in the working principle of the protection chip: IC: It is the core of the protection chip. It first samples the battery voltage and then issues various commands through judgment. MOS tube: It mainly acts as a switch.
2. The protection chip works normally: The MOS tube on the protection chip may be in the off state at the beginning. After the battery is connected to the protection chip, the MOS tube must be triggered first, and the P+ and P- terminals have output voltage. Common trigger methods-use one The wire shorts B- and P-.
3. Protection chip overcharge protection: connect a power supply higher than the battery voltage to P+ and P-, connect the positive pole of the power supply to B+, and connect the negative pole of the power supply to B-. After the power supply is connected, the battery starts to charge, and the current direction is as shown in the figure. The current of I1 shown starts from the positive pole of the power supply and flows through the battery, D1 and MOS2 to the negative pole of the power supply (MOS1 is short-circuited by D1 at this time). The IC uses the capacitor to sample the value of the battery voltage. When the battery voltage reaches 4.25v, the IC Send a command to make pin CO low. At this time, the current starts from the positive pole of the power supply and flows through the battery, D1, and reaches MOS2. As the gate of MOS2 is connected to CO, it is also low. MOS2 is turned off and the entire loop is Turn off, the circuit plays a protective role.
4. Protection chip over-discharge protection: After connecting a suitable load to P+ and P-, the battery starts to discharge its current direction as I2, and the current flows from the positive pole of the battery through the load, D2 and MOS1 to the negative pole of the battery. MOS2 is short-circuited by D2); when the battery is discharged to 2.5v, IC samples and issues a command to turn off MOS1, the circuit is disconnected, and the battery is protected.
5. Overcurrent protection: After connecting a suitable load to P+ and P-, the battery starts to discharge and its current direction is like I2. The current flows from the positive pole of the battery through the load, D2 and MOS1 to the negative pole of the battery. D2 short-circuit); when the load suddenly decreases, the IC samples the voltage generated by the sudden increase in current through the VM pin. At this time, the IC samples and issues a command to turn off MOS1, the circuit is disconnected, and the battery is protected.
6. Short circuit protection: After connecting the empty load to P+ and P-, the lithium iron phosphate battery starts to discharge its current direction is like I2. Short circuit); IC samples the voltage generated by the sudden increase in current through the VM pin. At this time, the IC samples and issues instructions to turn off MOS1, the loop is disconnected, and the battery is protected.
Working principle of balance of lithium battery protection board
The lithium battery protection board is the charge and discharge protection of the series lithium battery pack; when fully charged, it can ensure that the voltage difference between the single cells is less than the set value, so as to realize the equal charge of each single cell of the lithium battery pack and effectively improve The charging effect under the series charging mode is detected; at the same time, the overvoltage, undervoltage, overcurrent, short circuit, and overtemperature status of each single battery in the battery pack are detected to protect and extend the battery life; undervoltage protection enables each single cell Avoid battery damage due to over-discharge during use.
Commonly used equalization charging techniques for the equalization principle of lithium battery protection boards include constant shunt resistance equalization charging, on-off shunt resistance equalization charging, average battery voltage equalization charging, switched capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc.
When charging a group of lithium batteries in series, ensure that each battery is charged in a balanced manner, otherwise the performance and life of the entire group of lithium iron phosphate batteries will be affected during use. The existing single-cell lithium battery protection chips do not have a balanced charge control function. The balanced charge control function of a multi-cell lithium battery protection chip requires an external CPU; it is realized through serial communication with the protection chip, which increases the complexity of the protection circuit. The degree and difficulty of design reduce the efficiency and reliability of the system and increase the power consumption.
According to the needs of the application, the balancing principle of the lithium battery protection board can realize the protection and equalization of the power lithium battery pack of any structure and voltage level after changing the protection chip model and the number of series, the power level of the switching devices and the power consumption components in the circuit .
The above is the balanced working principle of the iron-lithium battery protection chip and the lithium battery protection board. The lithium iron phosphate battery protection board has the function of protecting the battery and avoiding battery overcharging. The protection chip controls the on and off of the shunt discharge branch switching device to achieve balanced charging. This solution is different from the traditional method of achieving balanced charging at the charger end, and reduces the cost of design and application of lithium battery pack chargers.