The circuit diagram and working principle of lithium battery protection board

Lithium battery protection board principle: The lithium battery protection board has different circuits and parameters depending on the use of IC, voltage, etc.

The normal working process of the lithium battery protection board is:

When the battery voltage is between 2.5V and 4.3V, the first pin and the third pin of DW01 output a high level (equal to the power supply voltage), and the second pin voltage is 0V. At this time, the voltage of the first leg and the third pin of DW01 will be respectively added to the 54th pin of 8205A, and the two electronic switches in 8205A are connected to each other because their G poles are 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-end of the protection plate are equivalent to direct communication, and the protection plate has a voltage output.

Overcharge protection board: It is necessary for the protection board to have the ability to prevent the voltage of the battery from exceeding the default value; over-discharge maintenance: It is necessary for the protection board to have the ability to prevent the voltage of the battery from falling below the default value.

2, current capacity,

(Over current protection current, short circuit protection)

Protection board as lithium batteries, security protection equipment, as well as in the normal operation of equipment within the current size, reliable work, and when the battery was accidentally when a short circuit or over current can rapid action, make the batteries are protected.

3.7 v lithium battery protection board schematic diagram

3, on resistance

Definition: when the charging current is 500 ma, the conduction resistance of MOS tube.

Due to the high work frequency communication equipment, data transmission requirements error rate is low, its rise and fall of the pulse sequence along the steep, so the output current of battery capacity and voltage stability requirement is high, thus protecting plate of MOS tube switch turn-on resistance is smaller, the single section batteries protective plate is usually in the 70 m Ω, such as too much communication equipment operation is not normal, such as mobile phone suddenly break line when call, the phone was disconnected, the phenomenon such as noise.

4, self-consumption current

Definition: The IC operating voltage is 3.6V. Under no-load conditions, the operating current flowing through the protection IC is generally extremely small.

The self-consumption current of the protection board directly affects the standby time of the battery, and the self-consumption current of the regular protection board is usually less than 10 microamperes.

5, mechanical function, temperature adaptability, antistatic ability

Protection board necessary to pass the national standard rules of sensation, impact experiments; Protection board can work safety in 40 to 85 degrees, can withstand the non touch of plus or minus 15kv ESD static test.

Lithium battery protection function is usually performed by protection circuit board and PTC synergy, protective plate is composed of electronic components, in - 40 ℃ ~ + 85 ℃ under the environment of moment accurately monitor batteries voltage and current charge and discharge circuit, and control current circuit on and off; PTC under the environment of high temperature is the main purpose of protection. Prevent the battery combustion, explosion and other malignant accidents.

[Tip] PTC is the abbreviation of English Positive temperature coefficient, meaning that positive temperature coefficient of resistance (the higher the temperature, the greater the resistance).The element can be over-current protection role, that is, to prevent the battery discharge temperature and unsafe large current charge and discharge.PTC devices of macromolecule polymer material, through the strict craft, by the polymer matrix tree vinegar and distribution in the conductive particles inside. Under normal circumstances, the conductive particles constitute a conductive path in the tree vinegar, characterized by low impedance device; When circuits have over-current phenomenon occurs, the large current flows through PTC produce heat to make polymer tree vinegar matrix volume expansion, and thus to cut off the connection between the conductive particles, and over-current protection circuit. When what fault solution, the components can be automatically restored to its original state, guarantee the normal work of the circuit.

A, lithium battery charge and discharge requirements

1. Lithium battery charging

Highest single section of lithium battery charging termination voltage of 4.2 V, can't overcharge, otherwise it will for the anode of lithium ion lost too much and make a battery scrap. When for lithium battery, should adopt the special constant current, constant voltage charger, constant current charging to first on both ends of the lithium battery voltage of 4.2 V, into constant-voltage charging mode; When constant voltage charging current 100 ma, should stop charging.

Charging current (MA) was 0.1 ~ 1.5 times the battery capacity, for example: 1350mah lithium batteries, the charging current can be controlled between 135mA and 2025mA. Conventional charging current can choose at about 0.5 times the battery capacity, charging time is about 2 ~ 3 hours.

2. The discharge of lithium-ion batteries

Due to the internal structure of the lithium battery, lithium ions cannot all move to the positive electrode during discharge, and a part of lithium ions must be retained at the negative electrode to ensure that lithium ions can be smoothly inserted into the channel during the next charging. Otherwise, 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 voltage at the end of discharge, that is, 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 is related to the battery capacity and discharge current. Battery discharge time (hours) = battery capacity / discharge current, and lithium battery discharge current (MA) should not exceed 3 times the battery capacity, for example: 1000mAh lithium battery, the discharge current should be strictly controlled within 3A. Otherwise the battery will be damaged.

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