Lithium battery protection board circuit principle

The lithium battery(rechargeable) are needed to protect, is determined by its own characteristics.Due to the lithium battery material itself determines its cannot be overcharge, discharge, over current, short circuit and charging and discharging, high accordingly lithium battery Li-ion battery components will always follow a delicate protection board and a piece of current fuse.

Lithium battery protection function

Lithium battery protection function is usually performed by protection circuit board and PTC current device coordination, protective plate is composed of electronic circuits, and 40 ℃ to + 85 ℃ under the environment of time accurate monitoring batteries voltage and circuit current and the control current loop in time on and off;PTC under the environment of high temperature prevent severe damage in the battery.

Ordinary li-ion battery protective plate usually include control IC, MOS switch, resistor, capacitor and auxiliary device FUSE, PTC, NTC, ID, memory, etc.Which control IC, in the case of normal MOS switch control, make batteries with the external circuit conduction, and when the batteries voltage loop current or exceed the specified value, it control the MOS switch off immediately, to protect the safety of the batteries.

In protecting plate under the condition of normal, for high level Vdd and Vss, VM as low level, the DO, CO for high level, when the Vdd and Vss, VM any parameter transformation, the level will change on the DO or CO.

The principle of lithium battery protection board

Lithium battery (rechargeable) are needed to protect, is determined by its own characteristics.Materials due to the lithium battery itself determines that it can't be overcharge, discharge, over current, short circuit and ultra high temperature charge and discharge, so the lithium lithium battery components will always follow a delicate protection board and a piece of current protecting device.

Lithium battery protection function is usually performed by protection circuit board and PTC current device coordination, protective plate is composed of electronic circuits, and 40 ℃ to + 85 ℃ under the environment of time accurate monitoring batteries voltage and circuit current and the control current loop in time on and off;PTC under the environment of high temperature prevent severe damage in the battery.

Ordinary li-ion battery protective plate usually include control IC, MOS switch, resistor, capacitor and auxiliary device FUSE, PTC, NTC, ID, memory, etc.Which control IC, in the case of normal MOS switch control, make batteries with the external circuit conduction, and when the batteries voltage loop current or exceed the specified value, it control the MOS switch off immediately, to protect the safety of the batteries.

In protecting plate under the condition of normal, for high level Vdd and Vss, VM as low level, the DO, CO for high level, when the Vdd and Vss, VM any parameter transformation, the level will change on the DO or CO.

: 1, detection of charging voltage in normal condition, Vdd gradually rise to CO comprised high level to low electric voltage between Vdd and VSS at ordinary times.

2, charging lifting voltage: under the charging status, gradually reduced to Vdd CO comprised low level to high voltage electricity at ordinary times between Vdd and VSS.

3, over discharge detection voltage: usually, Vdd gradually reduced to DO comprised high level to low electric voltage between Vdd and VSS at ordinary times.

4, remove over discharge voltage: in the condition of over discharge, Vdd gradually rose to DO comprised low level to high voltage electricity at ordinary times between Vdd and VSS.

5, over-current detection voltage: 1 in normal state, the VM to DO gradually changed from high level to low electric voltage between VM - VSS at ordinary times.

6 2 detection voltage, over current, under normal condition, the VM from the OV rise at a speed of more than 1 ms below 4 ms to DO comprised high level to low electric voltage between VM - VSS at ordinary times.

7, load short began voltage: in normal state, the VM to OV with 1 mu S above 50 mu S speed to DO comprised under high level to low electric voltage between VM - VSS at ordinary times.

8, charger detection voltage: in the condition of over discharge, VM to OV gradually decline to DO changed from low level to a high voltage between electric VM - VSS at ordinary times.

9, usually work consumption current: in normal condition, flow to VDD terminal current (IDD) is the current consumption usually work.

10, consumption over discharge current: in the condition of discharge, through the VDD terminal in the current (IDD) for exile current electricity consumption.

The typical lithium battery protection circuit

Due to the chemical characteristics of lithium-ion batteries, in the process of normal use, its internal chemical positive reaction of mutual transformation between electricity and chemical energy, but under certain conditions, such as the overcharge, overdischarge and overcurrent will cause a chemical reaction of the battery inside, after the side effects increase, will seriously affect the performance and service life of the battery, and can produce a large amount of gas, make the battery internal pressure increased rapidly after the explosion caused by security problems, so all the lithium battery requires a protection circuit, used for battery charge and discharge for effective monitoring, and in some conditions where the broken charger, in order to prevent damage to the battery discharge circuit

Below is a typical lithium battery protection circuit principle diagram.

As shown in the above, the protection circuit consists of two MOSFET (V1, V2) and a control IC (N1) plus some resistance capacity components.Control IC is responsible for monitoring the battery voltage and the loop current, and control the two MOSFET gate, MOSFET switch role in the circuit, respectively controls the charging circuit and discharge circuit of conduction and shutoff, C3 to delay capacitor, the circuit has over charging protection, discharge protection, over current protection and short circuit protection function, its working principle analysis is as follows:

1, the normal state

Circuit under normal conditions for N1 "CO" and "DO" feet high output voltage, both MOSFET in conduction state, the battery can be free to charge and discharge, because of the MOSFET conduction impedance is very small, usually less than 30 milliohm, so its conduction resistance have little impact on the performance of the circuit.Under the state protection circuit for the consumption of current mu A level, usually less than 7 mu A.

2, over charging protection

Lithium ion batteries requirement for constant current/constant voltage charging way, at the beginning of the charge, for the constant current charge, as the charging process, voltage rise to 4.2 v (according to the positive electrode material is different, some battery requires constant pressure value is 4.1 v), to a constant voltage charging until the current more and more small.If the battery in the process of charged, the charger circuit out of control, can make the battery voltage is more than 4.After 2 v to constant current charging, the battery voltage will continue to rise, when the battery voltage charged to more than 4.3 v, the battery's chemical side effects will aggravate, will lead to cell damage or security problems.In the battery with protection circuit, when the control IC detected the battery voltage at 4.28 v (the value is determined by the control IC, IC of different have different values), the "CO" feet turn from high voltage zero voltage, the V2 by conduction to shut off, so as to cut off the charging circuit, the charger can no longer on battery charging, overcharge protection effect.And as a result of the existence of the V2 own body diode VD2, the battery can be discharge by the diode to external load.In the control IC detected the battery voltage is more than 4.28 v between signal off V2, there is a delay time, the length of the delay time is determined by C3, usually set to 1 seconds, in order to avoid the error caused by interference judgment.

3, short circuit protection

In the process of load discharge the battery in, if the large loop current to give U > 0.9 v (the value is determined by the control IC, IC of different have different values), control IC is judged as load short circuit, the "DO" feet turn quickly by high voltage zero voltage, V1 from conduction to shut off, so as to cut off the discharge circuit, short circuit protection.Very short delay time of short circuit protection, usually less than seven microseconds.Its working principle and over current protection, just different judgment method, protect the delay time is different also.In addition to control IC, there is another important element in the circuit, is a MOSFET, it play the role of a switch in the circuit, because it directly through between the battery and the external load, therefore its conduction resistance have an impact on the performance of the battery, was elected with MOSFET is better, the conduction resistance is very small, internal resistance of battery pack is small, load ability is strong, at the time of discharge its consume less electricity.

4, over current protection

Due to the chemical characteristics of lithium ion battery, battery manufacturer specifies its maximum discharge current should not exceed 2 C (C = battery capacity per hour), when the battery more than 2 C discharge current, will result in permanent damage or security problems of the battery.Battery in the process of normal load discharge, discharge current after a series of two MOSFET, due to the conduction impedance MOSFET, will produce a voltage at both ends, the voltage U = I * RDS * 2, RDS for a single MOSFET turn-on, impedance control IC the "V -" on the foot of the testing voltage value, if the load for some reason cause abnormal, make loop current increases, when the large loop current to make U > 0.1 v (the value is determined by the control IC, IC of different have different values), the "DO" feet turn from high voltage zero voltage, V1 from conduction to shut off, thus cutting off the discharge circuit, the current in the circuit is zero, overcurrent protection effect.Detected in control IC over-current occurred between signal off V1, also have a delay time, the length of the delay time is determined by C3, usually for about 13 ms, in order to avoid the error caused by interference judgment.In the process of the control, the over-current detection value size depends not only on the components of the control IC, still depends on the conduction resistance of mosfets, when the greater the MOSFET conduction impedance to the same control IC, the smaller the value of overcurrent protection.

5, over discharge protection

The battery in the process of external load discharge, the voltage will gradually reduce with the discharge process, when the battery voltage drop to 2.5 v, flashing its capacity has been fully, at this time if you let the battery to discharge continue to load will cause permanent damage of the battery.In the process of battery discharge, when the control IC detected the battery voltage is lower than 2.3 v (the value is determined by the control IC, IC of different have different values), the "DO" feet turn from high voltage zero voltage, V1 from conduction to shut off, thus cutting off the discharge circuit, the battery can no longer to discharge the load, over discharge protection effect.And as a result of the existence of V1's own body diode VD1, the charger can through the diode for rechargeable batteries.Due to the over discharge protection in the state of the battery voltage is not able to reduce, therefore requires minimal consumption current protection circuit, the control IC will enter a state of low power consumption, the protection circuit power consumption will be less than zero.1 mu A.In the control IC detected the battery voltage is lower than 2.3 v to signal off V1, also have a delay time, the length of the delay time is determined by C3, usually about 100 milliseconds, in order to avoid the error caused by interference judgment.

In the process of the control, the over-current detection value size depends not only on the components of the control IC, still depends on the conduction resistance of mosfets, when the greater the MOSFET conduction impedance to the same control IC, the smaller the value of overcurrent protection.

5, short circuit protection

Battery on load discharge process, if the large loop current to give U > 0.9 V (the value is determined by the control IC, different IC have different values), control IC is judged as load short circuit, the "DO" foot will quickly at zero voltage by high voltage change, make the T2 by conduction to shut off, so as to cut off the discharge circuit, short circuit protection.Very short delay time of short circuit protection, usually less than seven microseconds.Its working principle and over current protection, just different judgment method, protect the delay time is different also.

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