Lithium battery protection plate principle

The reason why lithium batteries(rechargeable) need protection is determined by their own characteristics. Since the material of the lithium battery itself determines that it can not be overcharged, over-discharged, overflowed, short-circuited, and ultra-high temperature charged and discharged, the lithium battery lithium power assembly will always follow an exquisite protective plate and a current fuse.

The protective function of a lithium battery is usually performed by a protective circuit board and an electric current device such as a PTC. The protective plate is composed of electronic circuits that accurately monitor the voltage of the core and the charge and discharge loop at a time of -40 °C to +85 °C. Current, To control the current circuit in time; PTC prevents poor battery damage in high temperature environments.

Ordinary lithium battery protection panels usually include control ICs, MOS switches, resistors, capacitors and auxiliary devices FUSE, PTC, NTC, ID, memory, etc.. Among them, the control IC controls the MOS switch under all normal conditions, so that the core and the external circuit are turned on, and when the core voltage or loop current exceeds the specified value, it immediately controls the MOS switch off to protect the safety of the core.

Detailed analysis of protective plate principle of lithium battery

Under normal protection conditions, Vdd is high, Vss, VM is low, DO, CO is high, and when Vdd, Vss, VM any one parameter transformation, the level of DO or CO terminal will change.

1, overcharge detection voltage: In the usual state, Vdd gradually increases from high level to low level VDD-VSS voltage.

2, overcharge discharge voltage: Under charging state, Vdd gradually reduced to CO end from low level to high voltage VDD-VSS voltage.

3, over discharge detection voltage: In the usual state, Vdd gradually reduced from high level to low level VDD-VSS voltage.

4, over discharge voltage: In the state of over discharge, Vdd gradually rises to the VDD-VSS voltage when the D end changes from low to high.

5, over current 1 detection voltage: In the normal state, VM gradually rises to DO from high to low voltage VM-VSS voltage.

6, over current 2 detection voltage: In the normal state, VM from OV to the O end at a speed of 1ms or more than 4ms from high to low voltage VM-VSS voltage.

7, load short-circuit detection voltage: In the usual state, VM rises from OV to the O end at a speed of 1 μS or more than 50 μS from high to low VM-VSS voltage.

8, charger detection voltage: In the over-discharge state, VM gradually dropped to DO from low level to high level VM-VSS voltage.

Current is usually consumed when working: In the normal state, the current(IDD) of the VDD terminal is the current consumed when working.

Over-discharge consumes current: In the discharge state, the current(IDD) flowing through the VDD terminal is the over-discharge consumes current.

1, lithium battery charging:

According to the structural characteristics of the lithium battery, the maximum charging termination voltage should be 4.2 V, which can not be overcharged. Otherwise, the battery will be scrapped because the positive lithium ion is taken away too much. Its charge and discharge requirements are high, and special constant current and constant pressure chargers can be used for charging. Usually constant current charging to 4.2 V/section is transferred to constant pressure charging. When the constant pressure charging current is reduced to within 100mA, the charging should be stopped.

Charge current(mA) = 0.1 to 1.5 times

Battery capacity(such as 1350mAh batteries, whose charging current can be controlled between 135 and 2025mA). Conventional charging current can be selected at about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours.

2, the discharge of lithium battery

Due to the internal structure of the lithium battery, lithium ions can not all move to the positive pole during discharge, and some lithium ions must be retained at the negative pole to ensure that lithium ions can be smoothly embedded in the channel at the next charge. Otherwise, the battery life will be shortened accordingly. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to strictly limit the discharge termination minimum voltage, that is, lithium batteries can not be over-discharged. The discharge termination voltage is usually 3.0 V/section and the minimum can not be lower than 2.5 V/section. The battery discharge time is related to the battery capacity and discharge current. Battery discharge time(hours) = battery capacity/discharge current. Lithium battery discharge current(mA) should not exceed 3 times the battery capacity. (For example, a 1000mAH battery, the discharge current should be strictly controlled within 3A) otherwise the battery will be damaged.

3, the protective circuit of lithium battery

It consists of two field effect tubes and a special protection integrated block S-8232. The overcharge control tube FET2 and the over-discharge control tube FET1 are connected in series to the circuit. The protection IC monitors the battery voltage and controls it. When the battery voltage rises to 4.2 V, Over charge protection tube FET1 off, stop charging. In order to prevent erroneous actions, a delay capacitor is generally added to the external circuit. When the battery is in a discharge state, the battery voltage drops to 2.55 V, the over-discharge control tube FET1 shuts down and stops supplying power to the load. Over-current protection is to control the FET1 to stop the discharge to the load when there is a large current flowing through the load. The purpose is to protect the battery and the field effect tube.

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