Schematic diagram of lithium battery protection board

The lithium battery IC (overvoltage protection board is mainly composed of maintenance maintenance) and MOS tube (over-current maintenance), is used to protect lithium battery safety equipment. Lithium battery with large discharge current, low resistance, long life, no memory effect, such as widely used by people, lithium ion batteries in the use of banned overcharge, over discharge, short circuit, otherwise will make battery fire and blast killed defects, so the use of rechargeable lithium batteries have a maintenance board to protect the safety of the batteries.

1, the voltage protection ability

Over charging protection board: it is necessary to prevent the batteries voltage protection board beyond preset abilities over discharge maintenance: it is necessary to prevent the batteries voltage protection plate bottom in default of talents.

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Lithium battery protection board is mainly composed of maintenance IC (overvoltage maintenance) and MOS tube (over-current maintenance), is used to protect the safety of lithium-ion battery batteries equipment.Lithium battery has a large discharge current, low resistance, long life, no memory effect, such as widely used by people, lithium ion battery in the use of banned overcharge, over discharge, short circuit, otherwise will make battery fire and blast killed defects, so the use of rechargeable lithium batteries have a maintenance board to protect the safety of the batteries.

1, the voltage protection ability

Over charging protection board: it is necessary to prevent the batteries voltage protection board beyond preset abilities over discharge maintenance: it is necessary to prevent the batteries voltage protection plate bottom in default of talents.

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, 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, the power flow

Definition: IC work voltage of 3.6 v, a no-load condition, through the protection IC operating current, general minimal.

Protective plate of the power flow directly affect the battery standby time, usually rules to protect board since less than 10 microampere power flow.

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 15 kv ESD static test.

The characteristics of lithium battery charge and discharge protection circuit and working principle

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 PosiTIvetemperaturecoefficient, 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: 1350 mah lithium batteries, the charging current can be controlled between 135 mA and 2025 mA.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 lithium battery and discharging lithium ion can't all to move to the positive, you must retain part of lithium ions in the cathode, in order to make sure the next rechargeable lithium ion can flow in channel.Otherwise, the battery life will be shortened.In order to guarantee the graphite layer after discharge in the left part of the lithium ion, to strictly limit discharge termination of the lowest voltage, that is to say, the lithium battery can't discharge.Single section of lithium battery discharging termination voltage of 3.0 V, usually the lowest not less than 2.5 V.The time of the battery discharge and the battery capacity, the size of the discharge current.Battery discharge time (hours) = battery capacity/discharge current, and lithium battery discharge current (mA) should not be more than 3 times of battery capacity, for example: 1000 mah lithium batteries, the discharge current should be strictly controlled within the 3 a, or you will make a battery damage.

Second, the protection circuit

Protection circuit are usually made of control IC, MOs switch tube, blow out the fuse, components such as resistors, capacitors, as shown in figure 2.Normal circumstances, the control output signal control IC MOs switch tube conduction, batteries and the external circuit conduction, when the batteries voltage or loop current over specified value, it control the MOs tube shut off immediately, in order to protect the safety of the batteries.

Control IC built-in high precision voltage detection circuit and multilevel current detection circuit.Among them, the voltage detection circuit is to test the charging voltage, once reached its setting threshold (typically 3.9 V ~ 4.4 V), immediately enter into the state of over charging protection;2 it is to test the discharge voltage, once reached its setting threshold (typically 2.0 V ~ 3.0 V), immediately enter into the state of over discharge protection.

In this circuit, MOS switch tube use thin TSSOP - 8 or more SOT23-6 packaging form, its appearance is shown in figure 3.Some of these MOS switch tube containing a N channel field effect tube, such as FDMC7680, its (1) ~ (3) the feet for the S pole, G (4) feet, 5 ~ end feet for D, its internal structure as shown in figure 4.Some contain two N channel field effect tube, such as FDW9926A, 8205 a, its pin function related to packaging format, as shown in figure 5.

3.7 v lithium battery protection board schematic diagram

3.7 v lithium battery protection board schematic diagram

3.7 v lithium battery protection board schematic diagram

If prompt 】 【 control IC and MOs switch tube with a small circular concave points, then the pits to pin (1) by the foot;If no concave surface point, the component model label on the left side of the first pin for (1) the foot, the rest of the pin arrangement counterclockwise direction.In addition, when switch to MOS switch tube, need according to the actual line to judge the internal circuit, and thus for the correct replacement.

In addition, some lithium battery protection circuit also equipped with the NTC and ID signal form element.The NTC is the abbreviation of English Negative temperature coefficient, meaning that negative temperature coefficient of resistance.The components in the circuit is mainly overheating protection role, namely when the battery itself or its surroundings at higher temperatures, the NTC components resistance is reduced, use electrical equipment or charging equipment timely response, if the temperature exceeds a certain value, the protection system into the state, stop to charge and discharge.ID is the abbreviation of Identification, that is, the meaning of identification, the identification of components are divided into two kinds: one is the memory, often beast line interface, memory storage battery type, production date and other information;2 it is to identify the resistance, it both has the traceability and the limitation of the application of the product.

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