The principle of lithium battery protection board: The circuit and parameters of the lithium battery protection board are different according to the use of IC, voltage, etc.

　　The normal working process of lithium battery protection board is:

　　When the battery voltage is between 2.5V and 4.3V, both pins 1 and 3 of DW01 output high level (equal to the supply voltage), and the voltage of the second pin is 0V. At this time, the voltage of pin 1 and pin 3 of DW01 will be applied to pin 54 of 8205A respectively. The two electronic switches in 8205A are in the conducting state because their G pole is connected to the voltage from DW01, that is, two The electronic switches are all on. At this time, the negative electrode of the battery and the P- terminal of the protection board are equivalent to a direct connection, and the protection board has a voltage output.

　　Overcharge protection board: The protection board must have the ability to prevent the cell voltage from exceeding the preset value. Over-discharge maintenance: The protection board must have the ability to prevent the cell voltage from falling below the preset value.

　　2, current capability

　　(overcurrent protection current, short circuit protection)

　　As a safety protection device for lithium batteries, the protection board must not only work reliably within the normal operating current scale of the equipment, but also be able to act quickly when the battery is accidentally short-circuited or over-current, so that the batteries are protected.

　　3.7v lithium battery protection board schematic diagram

　　3, on-resistance

　　definition: when the charging current is 500mA, the on-resistance of the MOS tube.

　　Due to the high operating frequency of communication equipment, the low bit error rate required for data transmission, and the steep rising and falling edges of the pulse train, the current output capability and voltage stability of the battery are required to be high, so the MOS switch of the protection board is turned on The time resistance should be small. The single-cell battery protection board is usually "70mΩ. If it is too large, it will cause abnormal operation of the communication equipment, such as sudden disconnection of the mobile phone during a call, telephone connection failure, noise, etc.

　　4, self-consumption current

　　definition: IC operating voltage is 3.6V, under no-load conditions, the operating current flowing through the protection IC is generally very small.

　　The self-consumption current of the protection board directly affects the standby time of the battery. Generally, the self-consumption current of the protection board is less than 10 microamps.

　　5, mechanical function, temperature adaptability, antistatic ability

　　The protection board must be able to pass the sensation and impact test of the national standard rules; the protection board can work safely at 40 to 85 degrees, and can withstand the non-touch ESD static test of ±15KV.

　　The protection function of lithium battery is usually completed by the protection circuit board and PTC. The protection board is composed of electronic components. It can accurately monitor the voltage of the battery cell and the current of the charging and discharging circuit under the environment of -40℃～+85℃, and timely Control the on and off of the current loop; the main function of PTC is to protect in high temperature environments and prevent vicious accidents such as burning and explosion of the battery.

　　[Hint] PTC is the abbreviation of PosiTIvetemperaturecoefficient in English, which means positive temperature coefficient resistance (the higher the temperature, the greater the resistance). This component can play the role of over-current protection, that is, to prevent high-temperature discharge of the battery and unsafe high-current charging and discharging. The PTC device is made of high molecular material polymer through a rigorous process, consisting of a polymer resin matrix and conductive particles distributed inside. Under normal conditions, conductive particles form a conductive path in the resin, and the device exhibits low impedance; when there is an overcurrent phenomenon in the circuit, the heat generated by the large current flowing through the PTC causes the volume of the polymer resin matrix to expand, thus Cut off the connection between conductive particles, so as to protect the circuit from overcurrent. When the fault is resolved, the component can automatically return to the initial state to ensure the normal operation of the circuit.

　　1. Charge and discharge requirements for lithium batteries

　　1. Charging the lithium battery

　　The highest end-of-charge voltage of a single-cell lithium battery is 4.2V, and it cannot be overcharged, otherwise the battery will be scrapped due to the loss of too much lithium ions in the positive electrode. When charging the lithium battery, a dedicated constant current and constant voltage charger should be used. First, charge with constant current until the voltage at both ends of the lithium battery is 4.2V, then switch to constant voltage charging mode; when the constant voltage charging current drops to 100mA, Charging should be stopped.

　　The charging current (mA) can be 0.1 to 1.5 times the battery capacity, for example: a 1350mAh lithium battery, the charging current can be controlled between 135mA and 2025mA. The normal charging current can be selected at about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours.webcam factory

　　2. Discharge of lithium battery

　　Due to the internal structure of the lithium battery, all lithium ions cannot move to the positive electrode during discharge, and some lithium ions must be retained in the negative electrode to ensure that lithium ions can be inserted into the channel smoothly during the next charge. Otherwise, the battery life will be shortened. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to strictly limit the minimum discharge termination voltage, which means that the lithium battery cannot be over-discharged. The discharge termination voltage of a single-cell lithium battery is usually 3.0V, and the minimum cannot be lower than 2.5V. The length of battery discharge time is related to battery capacity and discharge current. Battery discharge time (hours) = battery capacity/discharge current, and the lithium battery discharge current (mA) should not exceed 3 times the battery capacity, for example: a 1000mAh lithium battery, the discharge current should be strictly controlled within 3A, otherwise it will The battery is damaged.