The principle of 3.7v 18650 battery pack protection board and the four functions of lithium battery protection circuit

　　The principle of 3.7v 18650 battery pack protection board and the four functions of lithium battery protection circuit. The lithium battery protection board is a circuit board composed of electronic components and PCB. Under a certain temperature and humidity environment, it is always ready to monitor the voltage of the battery cell and the current of the charging and returning circuit, and to control the on and off of the current circuit in a timely manner. Let’s talk about the principle of 3.7v 18650 battery pack protection board and the four functions of lithium battery protection circuit.

　　3.7v 18650 battery pack protection function

　　The protection function of the 3.7v 18650 battery pack is usually completed by a protection circuit board and current devices such as PTC. The protection board is composed of electronic circuits and can accurately monitor the voltage and charge and return circuit of the battery core at all times in an environment of -40°C to +85°C. current, and timely control the on-off of the current loop; PTC prevents severe damage to the battery in high-temperature environments.

　　Ordinary lithium battery protection boards usually include control IC, MOS switches, resistors, capacitors and auxiliary devices FUSE, PTC, NTC, ID, memory, etc. Among them, the control IC controls the MOS switch to turn on when everything is normal, so that the battery core is connected to the external circuit. When the battery core voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off to protect the battery core. Safety.

　　When the protection board is normal, Vdd is high level, Vss and VM are low level, DO and CO are high level. When any parameter of Vdd, Vss and VM changes, the level of DO or CO terminal will changes occur.

　　3.7v 18650 battery pack protection board principle

　　The reason why the 3.7v 18650 battery pack needs protection is determined by its own characteristics. Since the material of the 3.7v 18650 battery pack itself determines that it cannot be overcharged, overdischarged, overcurrent, short-circuited, or charged and discharged at ultra-high temperatures, the lithium battery assembly will always appear with a delicate protective board and a current fuse.

　　The protection function of lithium batteries is usually completed by a protection circuit board and current devices such as PTC. The protection board is composed of electronic circuits and can accurately monitor the voltage and charge return circuit of the battery core at all times in an environment of -40°C to +85°C. Current, timely control the on and off of the current loop; PTC prevents severe damage to the battery in high temperature environments.

　　Ordinary lithium battery protection boards usually include control IC, MOS switches, resistors, capacitors and auxiliary devices FUSE, PTC, NTC, ID, memory, etc. Among them, the control IC controls the MOS switch to turn on when everything is normal, so that the battery core is connected to the external circuit. When the battery core voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off to protect the battery core. Safety.

　　Four functions of lithium battery protection circuit

　　1. Overcharge protection

　　The principle of the overcharge protection IC is: when an external charger charges a lithium battery, the charging state needs to be terminated to prevent the internal pressure from rising due to temperature rise. At this time, the protection IC needs to detect the battery voltage. When it reaches 4.25V (assuming the battery overcharge point is 4.25V), the overcharge protection is activated, turning the power MOS from on to off, thereby stopping charging.

　　In addition, you must also pay attention to overcharge detection malfunctions caused by noise to avoid being judged as overcharge protection. Therefore, the delay time needs to be set, and the delay time cannot be shorter than the duration of the noise.

　　2. Over-discharge protection

　　In the case of over-discharge, the electrolyte decomposes, causing battery characteristics to deteriorate and reducing the number of charges. The use of lithium battery protection IC can avoid excessive discharge and realize battery protection function.

　　3. Overcurrent protection

　　Overcurrent or short circuit occurs due to unknown reasons (during discharge or the positive and negative electrodes are accidentally touched by metal objects). To ensure safety, the discharge must be stopped immediately.

　　When the discharge current is too large or a short circuit occurs, the protection IC will activate over (short circuit) current protection. At this time, the over current detection uses the Rds(on) of the power MOSFET as an inductive impedance to monitor the drop in its voltage. If If the overcurrent detection voltage is higher than the predetermined overcurrent detection voltage, the discharge will be stopped. Similarly, the overcurrent detection must also have a delay time to prevent malfunction when a sudden current flows in.

　　4. Short circuit protection

　　Prevent the battery from catching fire and exploding due to careless operation, directly connecting the positive and negative electrodes, and ensure safety during use and transportation.

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