1. The composition of the protection board of lithium battery
Its characteristics determine the reason why lithium battery (rechargeable) needs protection. The lithium battery material itself determines that it is not allowed over-charged, over-discharged, overcurrent, short-circuited. The lithium battery’s ultra-high temperature charging and discharging lithium battery components will always appear with an exquisite protection board and a current fuse. The protection circuit board and PTC usually complete the protection function of lithium batteries. The protection board is composed of electronic circuits. It can accurately monitor the battery cell’s voltage and the charging and discharging circuit current under the environment of -40℃ to +85℃. Control the current loop on and off; PTC prevents severe damage to the battery in a high-temperature environment.
The protection board usually includes a control IC, MOS switch, resistor, capacitor, and auxiliary device NTC, ID memory, etc. Among them, the control IC controls the MOS switch to turn on under all normal conditions to make the cell communicate with the external circuit. When the cell voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off (tens of milliseconds). Protect the safety of batteries. NTC is the abbreviation of the Negative temperature coefficient, which means a negative temperature coefficient. When the ambient temperature rises, its resistance decreases. The electrical equipment or charging equipment works to respond in time and control internal interruptions to stop charging and discharging. ID memory is often a single-wire interface memory. ID is the abbreviation of Identification, which means Identification, and stores information such as battery type and production date. It can play a role in product traceability and application restrictions.
2. The primary function of the protection board of lithium battery
Generally, Control (IC) detects and controls the cell voltage and the charging and discharging circuit’s working current and voltage at -25℃～85℃. Under all ordinary conditions, the C-MOS switch tube makes the cell and the protection circuit board a normal working state. When the cell voltage or the active current in the loop exceeds the comparison circuit’s preset value in the control IC, the CMOS turned off within 15-30ms. That is, close the battery discharge or charging circuit to ensure the user’s safety and the battery.
Working principle diagram of the protection board of battery:
As shown in the figure, the battery works for the IC, and the voltage is 2V-5V to ensure reliable operation.
As shown in the figure, the battery works for the IC, and the voltage is 2V-5V to ensure reliable operation.
1. Overcharge protection and overcharge protection recovery
When the battery is charging, and the voltage exceeds the set value VC (4.25-4.35V), VD1 flips to make Cout low, T1 ends, and charging stops. When the battery voltage drops to VCR (3.8-4.1V) when Cout becomes high, T1 turns 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) due to discharge, VD2 reverses, after a short time delay, Dout becomes low level and T2 ends. The discharging stops.
3. Over current and short circuit protection
When the charging and discharging loop current of the circuit exceeds the set value or short-circuited, the short-circuit detection circuit operates to turn off the MOS tube, and the wind cut off.
You can read the functions of main components of protection board here.