What's the Principle of Lithium Battery Protection Plate?

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.

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.

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 the 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 a 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 release 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.

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

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

Typical lithium battery Protection Circuit

Due to the chemical properties of lithium batteries, during normal use, the internal chemical reaction of electrical energy and chemical energy is converted into each other, but under certain conditions, If overcharging, over discharge, and over current will lead to chemical side reactions within the battery, this side reaction will seriously affect the performance and service life of the battery, and may produce a large amount of gas. The internal pressure of the battery rapidly increases and causes safety problems. Therefore, all lithium batteries need a protective circuit to effectively monitor the battery's charge and discharge state. And under certain conditions to close the charge and discharge circuit to prevent damage to the battery

The protection loop consists of two MOSFET(V1, V2) and a control IC(N1) plus some blocking components. The control IC is responsible for monitoring the battery voltage and circuit current and controlling the gates of two MOSFET. The MOSFET play a switching role in the circuit and control the steering and closing of the charging and discharge circuits, respectively. C3 is a delay capacitor. The circuit has the functions of overcharge protection, over discharge protection, over current protection and short circuit protection. Its working principle is analyzed as follows:

1, normal state

Under normal conditions, both the "C" and "D" feet of N1 are exported to high voltage, and both MOSFET are in a state of conduction. The battery is free to charge and discharge. Since the switching impedance of the MOSEFT is small, usually less than 30 mm, its conduction resistance has little effect on the performance of the circuit. The current consumed by the protection circuit in this state is μA, which is usually less than 7 μA.

The page contains the contents of the machine translation.