Design And Research Of Integrated Protection Circuit For Lithium Batteries

In recent years,with the development of the new energy automobile industry,the application of lithium battery is expanding in our daily life.Among them,the high-power lithium battery has achieved great development in the past few years.Because of the higher risk of power lithium battery,people put forward higher requirements for lithium battery protection circuit.Lithium battery protection circuit is an indispensable part of the battery,it can limit the battery voltage,current in a safe and reasonable range.its performance will directly affect the life of lithium battery,as well as safety.At present,the protection circuit is developing towards the direction of smaller area,higher voltage resistance and stronger reliability.Therefore,a lithium battery protection circuit with a withstand voltage of 25 V is designed in the paper,and its overvoltage protection voltage is 25 V,undervoltage protection voltage is 20 V,overcurrent protection current is 3A,and static working current is below 30 uA.Inside the circuit,we innovatively designs a series power supply double comparator structure.The comparator has a symmetrically distributed structure and can achieve railto-rail output.With proper bias,the differential amplifier circuit in the two comparators can supply power in series and work independently.Then the structure is simulated and the input and output voltage is analyzed to verify the feasibility of the structure.In order to match the double comparator in series,a symmetrical voltage reference source,a bias circuit and a voltage divider are designed.The total power consumption of the voltage detection circuit is reduced by nearly half.Secondly,a highly sensitive current sampling circuit is designed.It uses the difference between the source voltage of a pair of MOSFET and the voltage of the sampling resistance to compare and determine whether the current is too large.Such a circuit can detect extremely low voltage,thus reducing the resistance and power consumption of the sampling resistance.Next,another pair of MOSFET is used as a comparison to offset the temperature coefficient of the current sampling circuit,making its temperature drift close to zero.Then,the structure of the constant current circuit makes it not affected by the power supply voltage when detecting the current.In addition,the delay circuit of overcurrent protection is designed to solve the problem that overcurrent protection is triggered repeatedly.In order to reduce capacitance and other external components,the delay function is realized by digital circuit.The paper designs a power supply module and a clock module for the digital part.Finally,we integrates the modules of overcurrent detection,overvoltage detection and undervoltage detection.And through the appropriate circuit of their output terminal voltage matching,so that the entire circuit can correctly control the external MOSFET,to achieve the lithium battery protection circuit required functions.