Discharge management circuit for parallel lithium batteries

Abstract

The utility model relates to the technical field of lithium battery discharge, and discloses a discharge management circuit for parallel lithium batteries, which comprises discharge units with the same number as the parallel lithium batteries, and each discharge unit comprises a switch tube V1, a triode V2, a triode V3, a resistor R1 and a resistor R2. In actual use, each lithium battery is provided with a discharge unit, when the voltages of the lithium batteries connected in parallel are inconsistent, the high-voltage lithium batteries discharge through the corresponding discharge units, and when the voltages of all the lithium batteries are balanced, all the lithium batteries supply power again. Therefore, the situation that current flows backwards when all the lithium batteries are discharged is avoided; in addition, the whole discharging unit is simple in structure, only one switching tube, two triodes and two resistors are arranged, and compared with a mode that a power management chip is used for discharging balance, the cost is low, and the practical applicability is better.

Description

Technical Field

[0001] This utility model relates to the field of lithium battery discharge technology, specifically to a discharge management circuit for parallel lithium batteries. Background Technology

[0002] Lithium-ion batteries are widely used in various fields due to their high energy density, light weight, long lifespan, low self-discharge rate, rapid charging and discharging capabilities, and high safety. For example, in new energy vehicles, battery packs composed of a large number of lithium-ion batteries serve as the power source, and in some miniaturized devices, two or four lithium-ion batteries connected in parallel are often used for power supply.

[0003] During the use of lithium batteries, due to the difference in initial voltage and internal resistance, current backflow between lithium batteries may occur. This backflow may cause the electrolyte inside the lithium battery to decompose, thereby damaging the positive and negative electrode materials of the lithium battery and shortening the service life of the lithium battery.

[0004] Even worse, in extreme cases, reverse current can cause a short circuit inside the lithium battery, leading to overheating, swelling, or even explosion, resulting in a safety accident. Therefore, it is necessary to perform equal discharge on lithium batteries. Equal discharge can balance the performance of lithium batteries, prevent overcharging or over-discharging, and eliminate internal differences in the battery, thereby improving battery performance.

[0005] In addition, over-discharge protection must be considered when discharging lithium batteries. Over-discharge means that the battery continues to discharge even when the voltage drops below the rated voltage during the discharge process. For example, the rated voltage of an 18650 lithium battery is generally 2.5V. If it continues to discharge below this voltage, it will disrupt the internal chemical balance of the lithium battery, increase the internal resistance of the lithium battery, and significantly reduce the capacity of the lithium battery, thus affecting the working time.

[0006] Currently, most lithium-ion batteries use imported power management chips for discharge management, such as the Texas Instruments TPS82130SLR. For miniaturized devices using a smaller number of lithium-ion batteries, using imported power management chips results in higher costs and requires matching peripheral circuitry, leading to a more complex structure. Furthermore, the import of these chips is subject to policy restrictions, potentially creating a "chip bottleneck." Utility Model Content

[0007] In view of the shortcomings of the background technology, the present invention provides a discharge management circuit for parallel lithium batteries. The technical problem to be solved is that existing miniaturized devices that use a small number of lithium batteries as power sources have high costs and complex structures due to the need to use foreign power management chips for discharge management.

[0008] To solve the above technical problems, this utility model provides the following technical solution: a discharge management circuit for parallel lithium batteries, including a number of discharge units the same as the number of lithium batteries connected in parallel, wherein the discharge unit includes a switch V1, a transistor V2, a transistor V3, a resistor R1, and a resistor R2;

[0009] The first connection terminal of the switching transistor V1 is electrically connected to the output terminal of a lithium battery, and is also electrically connected to the emitter of the transistor V2.

[0010] The second connection terminal of the switching transistor V1 is electrically connected to the emitter of the transistor V3; the base of the transistor V2 is electrically connected to the collector of the transistor V2 and the base of the transistor V3, respectively, and is grounded through resistor R1; the second connection terminals of the switching transistors V1 of all discharge units are electrically connected to each other.

[0011] The third connection terminal of the switching transistor V1 is electrically connected to the collector of the transistor V3 and grounded through resistor R2.

[0012] In one embodiment, both transistors V2 and V3 are PNP type transistors.

[0013] In one embodiment, the switching transistor V1 is a PMOS transistor, with the drain of the PMOS transistor being the first connection terminal of the switching transistor V1, the source of the PMOS transistor being the second connection terminal of the switching transistor V1, and the gate of the PMOS transistor being the third connection terminal of the switching transistor V1.

[0014] In one embodiment, the resistors R1 and R2 have the same resistance value.

[0015] In one embodiment, the present invention further includes an over-discharge protection unit, which is electrically connected to the second connection terminal of the switching transistor and is used to output a low-level control signal when the voltage at the second connection terminal of the switching transistor is lower than the low-voltage threshold.

[0016] In one embodiment, the over-discharge protection unit also outputs a high-level control signal when the voltage at the second connection terminal of the switching transistor is higher than the high-voltage threshold.

[0017] In one embodiment, the over-discharge protection unit includes a comparator chip and a voltage divider branch, the voltage divider branch including a first voltage divider node and a second voltage divider node, the voltage of the first voltage divider node being greater than the voltage of the second voltage divider node;

[0018] The input terminal of the voltage divider branch is electrically connected to the second connection terminal of the switching transistor. The first voltage divider node is electrically connected to the high voltage comparison input pin of the comparator chip. The second voltage divider node is electrically connected to the low voltage input pin of the comparator chip. The output pin of the comparator chip is used to output the control signal.

[0019] In one embodiment, the over-discharge protection unit includes a comparator chip and a voltage divider branch, the voltage divider branch including a first voltage divider node and a second voltage divider node, the voltage of the first voltage divider node being greater than the voltage of the second voltage divider node;

[0020] The input terminal of the voltage divider branch is electrically connected to the second connection terminal of the switching transistor. The first voltage divider node is electrically connected to the low-voltage comparison input pin of the comparator chip. The second voltage divider node is electrically connected to the high-voltage input pin of the comparator chip. The output pin of the comparator chip is used to output the control signal.

[0021] In one embodiment, the voltage divider branch includes resistors R3, R4, and R5 connected in series. One end of resistor R3 is electrically connected to the second connection terminal of the switching transistor, the other end of resistor R3 is electrically connected to terminal 1 of the comparator chip, one end of resistor R3 is electrically connected to terminal 6 of the comparator chip, and the other end of resistor R3 is grounded.

[0022] In one embodiment, the resistance ratio of resistor R3 to resistor R4 is 23:1, and the resistance ratio of resistor R4 to resistor R5 is 1:22.

[0023] The beneficial effects of this utility model compared with the prior art are as follows: In actual use, this utility model sets a discharge unit for each lithium battery. When the voltage of the parallel lithium batteries is inconsistent, the high-voltage lithium battery will discharge first through the corresponding discharge unit. When the voltage of all lithium batteries reaches equilibrium, all lithium batteries will be powered again, thereby avoiding the situation of current backflow when all lithium batteries are discharging.

[0024] In addition, the entire discharge unit has a simple structure, with only one switching transistor, two transistors and two resistors. Compared with using a power management chip for discharge equalization, it is lower in cost and more practically applicable. Attached Figure Description

[0025] Figure 1 This is a circuit diagram of the discharge unit in the embodiment;

[0026] Figure 2 This is a circuit diagram of the over-discharge protection unit in the embodiment. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the present invention, and therefore only show the components relevant to the present invention.

[0028] like Figure 1As shown, a discharge management circuit for parallel lithium batteries includes discharge units in the same number as the number of lithium batteries connected in parallel. Each discharge unit includes a switch V1, a transistor V2, a transistor V3, a resistor R1, and a resistor R2.

[0029] Specifically, when there are two lithium batteries connected in parallel, this utility model includes two discharge units; when there are four lithium batteries connected in parallel, this utility model includes four discharge units; and when there are five lithium batteries connected in parallel, this utility model includes five discharge units.

[0030] In one implementation, the number of discharge units can be set according to actual needs, and there is no limitation here. One of the inventive points of this utility model is to set a separate discharge unit for each lithium battery.

[0031] Specifically, Figure 1 In the middle, the first connection terminal of the switching transistor V1 is used to electrically connect to the output terminal of a lithium battery, and is also electrically connected to the emitter of the transistor V2;

[0032] The second connection terminal of the switching transistor V1 is electrically connected to the emitter of the transistor V3; the base of the transistor V2 is electrically connected to the collector of the transistor V2 and the base of the transistor V3, and is grounded through resistor R1; the second connection terminals of the switching transistors V1 of all discharge units are electrically connected to each other.

[0033] The third terminal of the switching transistor V1 is electrically connected to the collector of the transistor V3 and grounded through resistor R2.

[0034] Taking the balancing of two parallel lithium batteries as an example, the working process of the two discharge units is as follows:

[0035] The two discharge units are designated as the first discharge unit and the second discharge unit, respectively. The lithium battery voltage connected to the first discharge unit is denoted as VL1, and the lithium battery voltage connected to the second discharge unit is denoted as VL2. During actual balancing, if VL1 and VL2 are not equal, the discharge unit with the larger voltage value will discharge first. Specifically, when VL1 is greater than VL2, transistor V2 in the first discharge unit is turned on and transistor V3 is turned off, while transistor V2 in the second discharge unit is turned off and transistor V3 is turned on. This turns off the switching transistor V1 in the second discharge unit, preventing VL2 from flowing back into VL1; the reverse is also true.

[0036] In practical use, this utility model sets up a discharge unit for each lithium battery. When the voltage of the parallel lithium batteries is inconsistent, the higher voltage lithium battery will discharge through the corresponding discharge unit first. When the voltage of all lithium batteries reaches equilibrium, all lithium batteries will be powered again, thereby avoiding the situation of current backflow when all lithium batteries are discharging.

[0037] In addition, the entire discharge unit has a simple structure, with only one switching transistor, two transistors and two resistors. Compared with using a power management chip for discharge equalization, it is lower in cost and more practically applicable.

[0038] Specifically, in this embodiment, both transistors V2 and V3 are PNP type transistors. Furthermore, transistors V2 and V3 can be of the 2SA1036 type. This type of transistor has an RDS of 27mΩ when VGS = -3.7V. For a typical power consumption device of 2Wh, the loss introduced by this circuit is only 0.027Wh, accounting for only 1% of the total power consumption.

[0039] Specifically, in this embodiment, the switching transistor V1 is a PMOS transistor. The drain of the PMOS transistor is the first connection terminal of the switching transistor V1, the source of the PMOS transistor is the second connection terminal of the switching transistor V1, and the gate of the PMOS transistor is the third connection terminal of the switching transistor V1. The type of PMOS transistor can be selected according to actual needs. For example, the type of PMOS transistor can be CJ2333.

[0040] In this embodiment, resistors R1 and R2 have the same resistance value. For example, the resistance value of resistor R1 can be 50KΩ.

[0041] In this embodiment, the present invention further includes an over-discharge protection unit, which is electrically connected to the second connection terminal of the switching transistor. The over-discharge protection unit is used to output a low-level control signal when the voltage at the second connection terminal of the switching transistor is lower than a low-voltage threshold. This control signal can be used as a signal to stop the lithium battery from supplying power; that is, when the control signal is active, the lithium battery stops supplying power, and when there is no control signal, the lithium battery can supply power normally.

[0042] In addition, in this embodiment, the over-discharge protection unit also outputs a high-level control signal when the voltage at the second connection terminal of the switching transistor is higher than the high voltage threshold.

[0043] Specifically, the over-discharge protection unit includes a comparator chip and a voltage divider branch, wherein the comparator chip is a hysteresis comparator chip; the voltage divider branch includes a first voltage divider node and a second voltage divider node, wherein the voltage of the first voltage divider node is greater than the voltage of the second voltage divider node;

[0044] The input terminal of the voltage divider branch is electrically connected to the second connection terminal of the switching transistor. The first voltage divider node is electrically connected to the high voltage comparison input pin of the comparator chip. The second voltage divider node is electrically connected to the low voltage input pin of the comparator chip. The output pin of the comparator chip is used to output control signals.

[0045] In one embodiment, the over-discharge protection unit includes a comparator chip and a voltage divider branch. The voltage divider branch includes a first voltage divider node and a second voltage divider node, wherein the voltage of the first voltage divider node is greater than the voltage of the second voltage divider node.

[0046] The input terminal of the voltage divider branch is electrically connected to the second connection terminal of the switching transistor. The first voltage divider node is electrically connected to the high voltage comparison input pin of the comparator chip. The second voltage divider node is electrically connected to the low voltage input pin of the comparator chip. The output pin of the comparator chip is used to output control signals.

[0047] One implementation circuit diagram of the over-discharge protection unit is as follows: Figure 2 As shown, in Figure 2 In this chip, the model number is CN302. Terminal 6 of the comparator chip is a high-voltage input comparator pin, terminal 1 of the comparator chip is a low-voltage input comparator pin, terminal 5 of the comparator chip is used to output control signals, terminal 2 of the comparator chip is grounded, and terminal 4 of the comparator chip is used to input the working voltage, which is 5V DC voltage.

[0048] exist Figure 2 In the circuit, the voltage divider branch includes resistors R3, R4 and R5 connected in series. One end of resistor R3 is electrically connected to the second connection terminal of the switching transistor, the other end of resistor R3 is electrically connected to the first terminal of the comparator chip, one end of resistor R3 is electrically connected to the sixth terminal of the comparator chip, and the other end of resistor R3 is grounded.

[0049] for Figure 2 The comparison chip shown can achieve over-discharge protection of lithium batteries and eliminate output disorder of back-end circuits caused by voltage instability by setting up and down thresholds.

[0050] When the lithium battery voltage is detected to be lower than the set down threshold, a control signal EN will be output to shut down the back-end power supply circuit, thereby preventing the lithium battery from continuing to discharge after reaching the protection voltage and causing damage.

[0051] When the lithium battery stops discharging, the voltage will rebound and exceed the downlink threshold. Based on the principle of hysteresis comparator, an uplink threshold is set at this time. The backend power supply circuit will only be turned on when the lithium battery voltage is higher than the uplink threshold, thus avoiding the backend power supply circuit being in a state of repeated switching.

[0052] The formulas for calculating the uplink and downlink thresholds are as follows:

[0053] V 上行 =((R20+R21+R22)÷R22)×Vref;

[0054] V 下行 =((R20+R21+R22)÷(R21+R22))×Vref;

[0055] Vref is the internal reference voltage of the comparator chip, typically 1.211V.

[0056] Taking over-discharge protection of 18650 lithium batteries as an example, V 上行 Set to 2.65V, V 下行 Set to 2.5V, we get R3 = 230kΩ, R4 = 10kΩ, and R5 = 200kΩ. At this time, the resistance ratio of R3 to R4 is 23:1, and the resistance ratio of R4 to R5 is 1:22.

[0057] During normal operation, pin 5 of the comparator chip N1 will output a high-level control signal to drive the back-end power supply circuit to work normally.

[0058] When the lithium battery discharge voltage drops to 2.5V, pin 5 will output a low-level control signal to cut off the power supply circuit at the back end, thereby preventing the lithium battery from discharging to a lower voltage and affecting the battery life.

[0059] Based on the above description and inspired by this utility model, those skilled in the art can make various changes and modifications without departing from the technical concept of this utility model. The technical scope of this utility model is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A discharge management circuit for parallel lithium batteries, characterized in that, It includes a number of discharge units that are connected in parallel with the number of lithium batteries. The discharge unit includes a switch V1, a transistor V2, a transistor V3, a resistor R1, and a resistor R2. The first connection terminal of the switching transistor V1 is electrically connected to the output terminal of a lithium battery, and is also electrically connected to the emitter of the transistor V2. The second connection terminal of the switching transistor V1 is electrically connected to the emitter of the transistor V3; the base of the transistor V2 is electrically connected to the collector of the transistor V2 and the base of the transistor V3, respectively, and is grounded through resistor R1; the second connection terminals of the switching transistors V1 of all discharge units are electrically connected to each other. The third connection terminal of the switching transistor V1 is electrically connected to the collector of the transistor V3 and grounded through resistor R2.

2. The discharge management circuit for a parallel lithium battery according to claim 1, characterized in that, Both transistors V2 and V3 are PNP type transistors.

3. The discharge management circuit for a parallel lithium battery according to claim 1, characterized in that, The switching transistor V1 is a PMOS transistor. The drain of the PMOS transistor is the first connection terminal of the switching transistor V1, the source of the PMOS transistor is the second connection terminal of the switching transistor V1, and the gate of the PMOS transistor is the third connection terminal of the switching transistor V1.

4. A discharge management circuit for a parallel lithium battery according to claim 1, characterized in that, The resistors R1 and R2 have the same resistance value.

5. A discharge management circuit for a parallel lithium battery according to any one of claims 1-4, characterized in that, It also includes an over-discharge protection unit, which is electrically connected to the second connection terminal of the switching transistor and is used to output a low-level control signal when the voltage at the second connection terminal of the switching transistor is lower than the low-voltage threshold.

6. A discharge management circuit for a parallel lithium battery according to claim 5, characterized in that, The over-discharge protection unit also outputs a high-level control signal when the voltage at the second connection terminal of the switching transistor is higher than the high-voltage threshold.

7. A discharge management circuit for a parallel lithium battery according to claim 6, characterized in that, The over-discharge protection unit includes a comparator chip and a voltage divider branch. The voltage divider branch includes a first voltage divider node and a second voltage divider node, wherein the voltage of the first voltage divider node is greater than the voltage of the second voltage divider node. The input terminal of the voltage divider branch is electrically connected to the second connection terminal of the switching transistor. The first voltage divider node is electrically connected to the high voltage comparison input pin of the comparator chip. The second voltage divider node is electrically connected to the low voltage input pin of the comparator chip. The output pin of the comparator chip is used to output the control signal.

8. A discharge management circuit for a parallel lithium battery according to claim 7, characterized in that, The comparator chip is model CN302. Terminal 1 of the comparator chip is the low-voltage input comparator pin, terminal 6 of the comparator chip is the high-voltage input comparator pin, terminal 5 of the comparator chip is used to output the control signal, terminal 2 of the comparator chip is grounded, and terminal 4 of the comparator chip is used to input the operating voltage.

9. A discharge management circuit for a parallel lithium battery according to claim 8, characterized in that, The voltage divider branch includes resistors R3, R4, and R5 connected in series. One end of resistor R3 is electrically connected to the second connection terminal of the switching transistor, the other end of resistor R3 is electrically connected to terminal 1 of the comparator chip, one end of resistor R3 is electrically connected to terminal 6 of the comparator chip, and the other end of resistor R3 is grounded.

10. A discharge management circuit for a parallel lithium battery according to claim 9, characterized in that, The resistance ratio of resistor R3 to resistor R4 is 23:1, and the resistance ratio of resistor R4 to resistor R5 is 1:22.

Images