Battery charging and discharging protection device and over-discharge protection method

Abstract

The present invention discloses a battery charge and discharge protection device and an over-discharge protection method to solve the technical problems that the existing battery management cannot guarantee the battery life and has insufficient compatibility. The present invention includes a battery management module, a control module, a switch module, and a voltage divider module. The switch module and the voltage divider module are connected in parallel to form a first node and a second node. The first node is connected to the protected battery, and the second node is connected to the discharge port / charging port. The input end of the battery management module is connected to the battery, and its output end is correspondingly connected to the input end of the control module. The switch module includes a switch control end correspondingly connected to the control module, and the switch module is turned on to short-circuit the voltage divider module. The beneficial effects of the present invention are: strong compatibility, improved battery life, and better prevention of overcharging and over-discharging.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply protection, and in particular to a battery charge and discharge protection device and an over-discharge protection method. Background Art

[0002] Lithium-ion batteries have many advantages such as higher energy density, higher battery voltage, less self-discharge, longer cycle life, and environmental protection. They are widely used in various electronic products. However, compared with lithium iron phosphate batteries, their lifespan (number of cycles) is relatively short, resulting in great waste. Therefore, it is of great significance to improve their service life.

[0003] The 2009 Volume 2 of Science and Technology Information records the "Charging Methods for Extending the Life of Lithium Batteries". The cycle life of lithium batteries can be extended by reducing the charging voltage and selecting the appropriate charging termination current. The 2016 Issue 03 of Automobile Technology discloses the "Effect of Discharge Depth on Battery Service Life". The data analysis shows that when the battery is used under DOD (20%-80%) and SOC (25%-75%) conditions, the increase in the charging AC internal resistance and the discharge AC internal resistance of the battery during the charging and discharging process is small, about 25%. After 500 cycles of charging and discharging, the battery thickness and AC internal resistance only increase by about 3.78% and 2.08%, and the capacity only decays by about 2.8%. However, in order to achieve the above purpose, the existing technology uses a specially designed low-voltage charger, which has poor compatibility, additional costs, and no protection measures against deep discharge. Summary of the invention

[0004] The present invention provides a battery charge and discharge protection device and an over-discharge protection method to solve the technical problems that the existing battery management cannot guarantee the battery life and has insufficient compatibility.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A battery charge and discharge protection device is designed, comprising a battery management module, a control module, a switch module, and a voltage divider module. The switch module and the voltage divider module are connected in parallel to form a first node and a second node. The first node is connected to a protected battery, and the second node is connected to a discharge port / charging port. The input end of the battery management module is connected to the battery, and the output end thereof is correspondingly connected to the input end of the control module. The switch module comprises a switch control end correspondingly connected to the control module, and the voltage divider module can be short-circuited when the switch module is turned on.

[0007] Furthermore, the switch module is an NMOS switch tube Q3, whose drain is connected to the first node, whose source is connected to the second node, and whose gate is the above-mentioned switch control terminal.

[0008] Furthermore, a low-power drive circuit is connected between the control module and the NMOS switch tube Q3 , the output end of the drive circuit is connected to the gate of the NMOS switch tube Q3 , and the input end thereof is connected to the output end of the control module.

[0009] Furthermore, the voltage divider module is a diode, a positive electrode of which is connected to the second node, and a negative electrode of which is connected to the first node.

[0010] Furthermore, the output end of the battery management module is connected to a charging switch and a discharging switch, the charging switch includes a charging control end and a charging path, the discharging switch includes a discharging control end and a discharging path, the charging control end and the discharging control end are connected to the output end of the battery management module, and the charging path and the discharging path are connected and arranged between the battery and the first node.

[0011] Furthermore, the charging switch is a MOS tube Q1, and the discharging switch is a MOS tube Q2.

[0012] Furthermore, the control module includes a USB interface and an SMBUS interface. The USB interface is used to connect to a computer to update the program, and the SMBUS interface outputs battery information, and a charger or a power-consuming device (such as a camera) can read the battery information through the SMBUS.

[0013] A battery over-discharge protection method is also designed, using the above battery charge and discharge protection device, comprising:

[0014] Charge the battery until it reaches the full voltage, then turn off the power and leave it alone. If the battery voltage remains unchanged before and after leaving it alone, this voltage is recorded as 100% voltage. If the battery voltage changes before and after leaving it alone, continue charging and leave it alone until the battery voltage remains unchanged.

[0015] Discharge the battery to the set termination voltage, then cut off the power and leave it alone. If the battery voltage remains unchanged before and after leaving it alone, this voltage is recorded as 0% voltage. If the battery voltage changes before and after leaving it alone, continue discharging and leave it alone until the battery voltage remains unchanged.

[0016] The above charge and discharge cycles are repeated for more than 2 times to correct the internal parameters of the battery management module; when the battery is discharged to the termination voltage, the battery power supply is disconnected to achieve over-discharge protection of the battery.

[0017] Furthermore, the batteries are in groups of 4, and the fully charged voltage of each group is 3.6V.

[0018] Furthermore, during the charging process, the charging voltage is 16.8V, the charging rate is set to 0.2C, the charging current is less than 0.2A, and the standby time after charging is 2h; during the discharging process, the discharge rate is 0.2C, and the standby time after discharging is 5h.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are:

[0020] 1. The present invention is provided with a microcontroller that communicates with the management chip in the battery and a MOS tube and a diode connected to the controller, so as to complete the function of low-voltage charging. The user does not need to replace the charger to achieve the demand for improving the battery life, and has strong compatibility.

[0021] 2. The present invention is based on impedance tracking technology, optimizes the design of fuel gauge parameters, and improves the battery pack 0 capacity voltage threshold and discharge cut-off voltage threshold. While extending the battery life, it can also ensure that the discharge slope of the real-time capacity and percentage in the constant power mode is consistent during the process of discharging the battery pack from 100% to 0%, thereby preventing the serious deviation of the battery pack's power indication caused by a single increase in the discharge cut-off voltage, and preventing the phenomenon of too fast capacity drop at the end of the discharge process, which affects the terminal user's experience, and avoiding abnormal shutdown of the terminal equipment and other malfunctions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The circuit diagram of the battery charging and discharging protection device of the present invention.

[0023] Figure 2 FIG. 4 is a circuit diagram of the intelligent battery management circuit of the present invention.

[0024] Figure 3 FIG. 4 is a circuit diagram of a MOS driving circuit of the present invention. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention are described below in conjunction with the accompanying drawings and examples. However, the following examples are only used to illustrate the present invention in detail and do not limit the scope of the present invention in any way.

[0026] The programs involved or relied upon in the following embodiments are all conventional programs or simple programs in the technical field, and those skilled in the art can make conventional selections or adaptive adjustments according to specific application scenarios.

[0027] The unit modules, parts, structures, mechanisms, sensors and other devices involved in the following embodiments are all conventional commercially available products unless otherwise specified.

[0028] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. The terms "first", "second", etc. involved in the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0029] Embodiment 1: A battery charge and discharge protection device, see Figure 1 , intelligent battery management circuit BQ40Z50, the input end is connected to the battery pack to obtain the voltage and internal resistance of the battery pack, the two output ends above are connected to the charging MOS (Q1) and the discharging MOS (Q2) respectively, the output end on the right is connected to the input end of the microcontroller, the output end of the microcontroller is connected to the input end of the MOS drive circuit, and the output end of the MOS drive circuit is connected to the gate of the main circuit switch Q3. MOS tube Q3 and diode D1 are connected in parallel, the drain of Q3 is connected to the negative electrode of D1 to form the first node, the source of Q3 is connected to the positive electrode of D1 to form the second node, the first node is connected to the source of Q2, and the second node is connected to the power supply port PACK+. The SMBUS communication interface of the microcontroller is connected to the charger or electrical equipment, and outputs the battery information obtained from the intelligent battery management circuit.

[0030] The above-mentioned microcontroller adopts the STM32F103RCT6 single-chip microcomputer, has a low power consumption mode, and has a USB function, and can be connected to a computer USB interface to directly update the program.

[0031] The above Q3 is an NMOS tube IRFH7004, which requires a special NMOS driver LTC7004, see Figure 3 , NMOS has a smaller on-resistance and is more suitable for high current discharge applications. D1 uses a low forward voltage Schottky diode because a suitable forward voltage drop can achieve an ideal full charge voltage, and a low forward voltage drop can reduce heat generation during charging.

[0032] When the battery voltage is too low and needs to be charged, a standard charger is used to start charging. Q3 is normally connected. Since the on-resistance of Q3 is much smaller than that of diode D1, it is equivalent to diode D1 being short-circuited. The microcontroller reads the battery pack information from the intelligent battery management circuit in real time. When the battery pack is charged to the set voltage value, the microcontroller issues an instruction to disconnect Q3 through MOS drive circuit 1 and switch to diode bypass charging. Due to the forward voltage drop of the diode, the voltage applied to the battery pack is relatively reduced after voltage division, thereby reducing the charging voltage. Moreover, the voltage drop of the forward conduction of the diode is a fixed value and does not affect the charging current. If conventional voltage divider devices such as resistors are used, the voltage drop of the resistor changes greatly with the change of the charging current, and the power supply cannot be completed. When the current is 0 when fully charged, the voltage drop across the resistor will also be 0, which will not achieve the purpose of reducing the charging voltage for the battery pack.

[0033] The above intelligent battery management circuit increases the discharge undervoltage protection threshold of the battery pack. When the discharge reaches the set threshold, Q2 is turned off to prevent the battery from over-discharging. By lowering the charge overvoltage protection threshold of the battery pack, when the charge reaches the set threshold, Q1 is turned off to prevent the battery from overcharging.

[0034] Example 2: The battery pack uses 4 groups of lithium-ion batteries in series (cell model is Panasonic NCR18650GA, nominal voltage is 3.6V), Q1 and Q2 use PSMN1R5-30YLC (Vds is 30V, on-resistance is 1.55mΩ), D1 uses PMEG060V100EPD (forward voltage drop is 0.325V at 1A), Q3 uses IRFH7004 (Vds is 40V, on-resistance is 1.1mΩ), PCAK+ charging voltage is 16.8V, the discharge undervoltage protection threshold set by the intelligent battery management circuit is 11V, when the battery voltage is lower than 11V during the discharge process, Q2 is turned off to prevent over-discharge. The charging overvoltage protection threshold is 16.5V, when the battery voltage is higher than 16.5V during the charging process, Q1 is turned off to prevent overcharging. When the intelligent battery management circuit detects that the battery voltage is 16.4V, it indicates that charging is about to be completed. At this time, Q3 is cut off to adopt step-down charging to extend the battery life.

[0035] Before use, the internal configuration parameters of BQ40Z50 need to be corrected. Specifically: A. Use PACK+16.8V for charging, set the charging rate to 0.2C, charge until the current is less than 0.2A, and then put the battery in a standby state for 2 hours. B. Then start discharging, set the discharge rate to 0.2C, stop discharging after discharging to the termination voltage, and then put the battery in a standby state for 5 hours. Steps A and B are collectively called 1 cycle. After the battery has undergone 2 cycles, the internal configuration parameters of BQ40Z50 have been corrected. If the discharge cut-off voltage is simply increased, the battery pack's power indication will have serious deviations, and at the end of the discharge process, the capacity will drop too fast, affecting the experience of the terminal user, and even causing abnormal shutdown of the terminal device and other faults. After adopting the above parameter configuration method, the battery pack's 0 capacity voltage threshold and discharge cut-off voltage threshold are increased. While extending the battery life, it can also ensure that the discharge slope of the real-time capacity and percentage in the constant power mode is consistent during the discharge of the battery pack from 100% to 0%.

[0036] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, those skilled in the art will appreciate that, without departing from the spirit of the present invention, the specific parameters in the above embodiments may be changed to form a plurality of specific embodiments, which are all within the common variation range of the present invention and will not be described in detail herein.

Claims

1. A battery charge and discharge protection device, characterized in that: It includes a battery management module, a control module, a switch module, and a voltage divider module. The switch module and the voltage divider module are connected in parallel to form a first node and a second node. The first node is connected to the protected battery, and the second node is connected to the discharge port / charging port. The input end of the battery management module is connected to the battery, and the output end thereof is correspondingly connected to the input end of the control module. The switch module includes a switch control end correspondingly connected to the control module. When the switch module is turned on, the voltage divider module can be short-circuited. The switch module is an NMOS type switch tube Q3, whose drain is connected to the first node, whose source is connected to the second node, and whose gate is the switch control end; the voltage divider module is a diode, whose anode is connected to the second node, and whose cathode is connected to the first node.

2. The battery charge and discharge protection device according to claim 1, characterized in that: A low-power drive circuit is connected between the control module and the NMOS switch tube Q3 , the output end of the drive circuit is connected to the gate of the NMOS switch tube Q3 , and the input end thereof is connected to the output end of the control module.

3. The battery charge and discharge protection device according to claim 1, characterized in that: The output end of the battery management module is connected to a charging switch and a discharging switch, the charging switch includes a charging control end and a charging path, the discharging switch includes a discharging control end and a discharging path, the charging control end and the discharging control end are connected to the output end of the battery management module, and the charging path and the discharging path are connected and arranged between the battery and the first node.

4. The battery charge and discharge protection device according to claim 3, characterized in that: The charging switch is a MOS tube Q1, and the discharging switch is a MOS tube Q2.

5. The battery charge and discharge protection device according to claim 1, characterized in that: The control module includes a USB interface and an SMBUS interface.

6. A battery over-discharge protection method, relating to the battery charge and discharge protection device according to claim 1, characterized in that: include: Charge the battery, and when the battery reaches the full-charge voltage, turn off the power and leave it until the voltage is stable, measure the battery voltage, and record it as 100% voltage; Discharge the battery to the set termination voltage, turn off the power and leave it until the voltage is stable, measure the battery voltage, and record it as 0% voltage; Repeat the above charge and discharge cycles for more than 2 cycles to correct the internal parameters of the battery management module; Connect the battery management module with corrected parameters to the battery, and when it is detected that the battery is discharged to the termination voltage, disconnect the battery power supply to achieve over-discharge protection.

7. The battery over-discharge protection method according to claim 6, characterized in that: The battery comprises four groups connected in series, and the full-charge voltage of each group of the batteries is 3.6V.

8. The battery over-discharge protection method according to claim 7, characterized in that: During the charging process, the charging voltage is 16.8V, the charging rate is set to 0.2C, the charging current is less than 0.2A, and the standby time after charging is 2h; during the discharging process, the discharge rate is 0.2C, and the standby time after discharge is 5h.

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