CN221380592U - A self-power-off protection circuit for lithium battery BMS - Google Patents

Abstract

The utility model discloses a self-power-off protection circuit for a lithium battery BMS, including an optical coupler, a power supply, a switch, a first MOS tube, a second MOS tube, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a capacitor, a first diode, a second diode, and a third diode; the input end of the optical coupler is connected to the fault trigger protection pin of the BMS, and the output end of the optical coupler is connected to the gate of the first MOS tube through the third diode; the drain of the second MOS tube is connected to the power input circuit of the BMS. The utility model realizes power-off when the BMS system fails and triggers protection through its own electrical characteristics, avoiding the discharge of a tiny current of the lithium battery due to the power consumption of the BMS itself, and causing over-discharge of the battery under long-term unmanned intervention, thereby improving the operability of the battery, extending its service life, and avoiding battery safety hazards caused by over-discharge.

Description

A self-power-off protection circuit for lithium battery BMS

Technical Field

The utility model relates to the technical field of lithium batteries, in particular to a self-power-off protection circuit for a lithium battery BMS.

Background technique

At present, lithium-ion batteries have been widely used as vehicle-mounted power battery packs in various types of flatbed trucks, electric forklifts, and unmanned guided vehicles (AGVs) due to their excellent charging and discharging characteristics, light weight, maintenance-free, and long service life. However, in actual application, due to improper human management and maintenance, battery packs often over-discharge.

For example, when the AGV vehicle is working, it is not charged in time, causing the low voltage protection to be triggered (when the protection is triggered, the battery capacity is usually below 5%). Although the battery management system (BMS) will actively disconnect the load circuit to avoid further discharge of the battery pack, the BMS circuit is still connected to the battery pack through the switch at this time. Since the power supply of its own circuit components is still maintained by the battery, once there is no intervention for a long time (depending on the battery capacity, usually 3-7 days), the battery cell voltage will be directly pulled down to the over-discharge state. At this time, even if you want to charge, the charging control circuit cannot be started due to the low battery voltage, resulting in failure to charge. Therefore, even if you find a way to charge the battery directly, most chargers will not work because they detect abnormal voltage; even if there is a way to restore the charge, the battery cell will also undergo lithium precipitation due to over-discharge, causing the internal resistance of the battery to increase, seriously damaging its life, and even causing fire and explosion accidents in extreme cases.

Utility Model Content

The purpose of the utility model is to provide a self-power-off protection circuit for a lithium battery BMS, which can disconnect the BMS circuit from the battery when the BMS triggers the protection, so as to avoid continued discharge loss of the lithium battery pack, thereby achieving the goal of not causing over-discharge to the battery pack even if it is shelved for a long time.

The technical solution adopted by the utility model is:

A self-power-off protection circuit for a lithium battery BMS, comprising an optical coupler K1, a power supply, a switch S1, a first MOS tube V5, a second MOS tube V8, a first resistor R75, a second resistor R76, a third resistor R77, a fourth resistor R78, a fifth resistor R89, a capacitor C71, a first diode VD28, a second diode VD29, and a third diode VD32;

The input end of the optical coupler K1 is connected to the fault trigger protection pin of the BMS, the output end of the optical coupler K1 is connected to the gate of the first MOS tube V5 through the third diode VD32, the gate of the first MOS tube V5 is connected to the third resistor R77 and one end of the fourth resistor R78 at the same time, the third resistor R77 and the fourth resistor R78 constitute a voltage divider circuit, wherein the other end of the fourth resistor R78 is grounded, the other end of the third resistor R77 is grounded through the capacitor C71 and the first resistor R75 in sequence, and the other end of the third resistor R77 is connected to the cathode of the first diode VD28, and the anode of the first diode VD28 is grounded; the capacitor The common connection end of C71 and the first resistor R75 is connected to the positive electrode of the power supply through the switch S1, and is also connected to the source of the second MOS tube V8; the drain of the first MOS tube V5 is connected to the gate of the second MOS tube V8 through the fifth resistor R89, the gate of the second MOS tube V8 is respectively connected to one end of the second resistor R76 and the positive electrode of the second diode VD29, and the lead end of the second resistor R76 and the negative electrode of the second diode VD29 are simultaneously connected to the source of the second MOS tube V8; the drain of the second MOS tube V8 is connected to the power input circuit of the BMS.

The RC circuit composed of the first resistor R75 and the capacitor C71 has a value of 10 MΩ and a value of 0.1 uF.

The first MOS tube V5 adopts N-channel small signal MOSFET 2N7000 or VN10KN to control the on and off of the second MOS tube V8.

The second MOS tube V8 adopts a P-channel high-current MOSFET IRF9640PBF, which is used to turn on or off the working power supply of the BMS main circuit.

It also includes a sixth resistor R12 and a seventh resistor R13. The sixth resistor R12 is connected in series between the fault trigger protection pin of the BMS and the input end of the optocoupler K1. The resistor is used as a current limiting resistor to prevent K1 from receiving excessive current shock and improve circuit stability. One end of the seventh resistor R13 is connected to the output end of the optocoupler K1, and the other end is grounded. The resistor is used as a pull-down resistor to clamp the pin to a low level when there is no output at the output end of K1.

The power source is a 24V battery pack, and the second diode VD29 adopts an 8.2V voltage regulator diode.

The utility model is used in series connection at the power input end of the lithium battery pack BMS. After adopting the circuit, even if the power switch of the battery is not turned off normally due to improper daily management, since the first resistor and the voltage-dividing resistor arranged between the positive and negative poles of the power supply at the input end of the circuit constitute an extremely high resistance of more than 10M, its power consumption is lower than the normal self-consumption of the battery cell and can be almost negligible, and the voltage disconnection of the subsequent circuit can be realized. Compared with the existing circuit, the standby time of the battery pack can be greatly extended, the daily use and maintenance are convenient, the safety hazard caused by over-discharge of the battery cell is avoided, the battery failure caused thereby is reduced, and even the cost of replacing the battery is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a circuit diagram of the utility model.

Detailed ways

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

As shown in FIG1 , the utility model includes an optical coupler K1, a power supply, a switch S1, a first MOS tube V5, a second MOS tube V8, a first resistor R75, a second resistor R76, a third resistor R77, a fourth resistor R78, a fifth resistor R89, a capacitor C71, a first diode VD28, a second diode VD29, and a third diode VD32;

The input end of the optical coupler K1 is connected to the fault trigger protection pin of the BMS, the output end of the optical coupler K1 is connected to the gate of the first MOS tube V5 through the third diode VD32, the gate of the first MOS tube V5 is connected to the third resistor R77 and one end of the fourth resistor R78 at the same time, the third resistor R77 and the fourth resistor R78 constitute a voltage divider circuit, wherein the other end of the fourth resistor R78 is grounded, the other end of the third resistor R77 is grounded through the capacitor C71 and the first resistor R75 in sequence, and the other end of the third resistor R77 is connected to the cathode of the first diode VD28, and the anode of the first diode VD28 is grounded; the capacitor The common connection end of C71 and the first resistor R75 is connected to the positive electrode of the power supply through the switch S1, and is also connected to the source of the second MOS tube V8; the drain of the first MOS tube V5 is connected to the gate of the second MOS tube V8 through the fifth resistor R89, the gate of the second MOS tube V8 is respectively connected to one end of the second resistor R76 and the positive electrode of the second diode VD29, and the lead end of the second resistor R76 and the negative electrode of the second diode VD29 are simultaneously connected to the source of the second MOS tube V8; the drain of the second MOS tube V8 is connected to the power input circuit of the BMS;

It also includes a sixth resistor R12 and a seventh resistor R13. The sixth resistor R12 is connected in series between the fault trigger protection pin of the BMS and the input end of the optocoupler K1. The resistor is used as a current limiting resistor to prevent K1 from receiving excessive current shock and improve circuit stability. One end of the seventh resistor R13 is connected to the output end of the optocoupler K1, and the other end is grounded. The resistor is used as a pull-down resistor to clamp the pin to a low level when there is no output at the output end of K1.

In actual use, the RC circuit composed of the first resistor R75 and the capacitor C71, the first resistor R75 has a value of 10MΩ, and the capacitor C71 has a value of 0.1uF. The first MOS tube V5 adopts N-channel small signal MOSFET 2N7000 or VN10KN to control the on and off of the second MOS tube V8. The second MOS tube V8 adopts P-channel high current MOSFETIRF9640PBF to turn on or off the working power supply of the BMS main circuit. The power supply is a 24V battery pack, and the second diode VD29 adopts an 8.2V voltage regulator diode, which can meet the protection of the AGV charging module of the BSM with a single-chip microcomputer model of C8051F041. As shown in the figure, the trigger protection pin of the single-chip microcomputer D1 is connected to the 55 pin.

Specifically, in a 24V battery system: S1 is closed, and the characteristic of capacitor blocking direct current and passing alternating current is utilized. The first capacitor C71 is instantly turned on to add the cell voltage +24V to the 1st pin of the N-channel first MOS tube V5. The 2-3 pins of the first MOS tube V5 are turned on when it is working. The second diode VD29 clamps the 1st pin of the P-channel second MOS tube V8 to 8.2V. The 2-3 pins of the second MOS tube V8 are closed when it is working, and the current is passed to the subsequent circuits, and the voltages required by the BMS circuit and the single-chip computer C8051F041 (D1) are provided through the inductor L1, the power conversion circuit, etc. The circuits connected to other pins on the single-chip computer D1 and the BMS circuits connected to the V8 output pins are omitted in Figure 1.

After the microcontroller D1 works, it pulls the corresponding pin 55 to a high level, triggers the optical coupler AQY210EH (K1), and continuously provides the first MOS tube V5 with a maintenance working voltage, so that the first MOS tube V5 always remains in the on working state. At this time, the subsequent BMS circuit obtains the required voltage and starts working.

When the BMS system fails and needs to trigger protection, the pin 55 of the D1 single-chip computer changes from a high level to a low level. Since the pin 1 of the optocoupler K1 is at a low level, the pin 3 of the optocoupler K1 is immediately pulled low. At this time, the capacitor C71 is in an open circuit state for DC, so the pin 1 of the first MOS tube V5 stops working due to the low level, so the second MOS tube V8 also stops working. Even if the switch S1 is still in a closed state, the input of the power supply of the subsequent BMS circuit is in a no-input voltage state at this time. At this time, since the first resistor R75 is 10M ohms, it means that there is only 2.4uA of power consumption on the resistor, and the capacitor C71 is in an open circuit state under the DC state, so the entire circuit is in a completely power-off state and will not consume power to the battery cell. The first diode VD28 can accelerate the discharge of the capacitor C71, and thus will not affect the next startup of the BMS system.

When it is necessary to restart the power, just open and then close the switch S1, and the entire BMS circuit can work normally.

In summary, the actual working process of this device is divided into three stages:

In the first stage, the BMS circuit is turned on. After the switch S1 is closed, the current instantly passes through the capacitor C71, turning on the first MOS tube V5, and clamping the pin 1 of the second MOS tube V8 to the turn-on voltage through the second diode VD29. At this time, the pins 2 and 3 of the second MOS tube V8 are turned on, and the current can enter the BMS circuit and the single-chip computer D1, providing the required voltages at all levels for the BMS development board and the MCU.

The second stage is the work maintenance stage. When the single-chip computer D1 or MCU is turned on and runs the program, the voltage of the corresponding control pin is pulled high. This pin triggers the optical coupler to continuously supply power to the first MOS tube V5, so that the BMS circuit can continue to work.

The third stage is the important power-off protection stage. When the system fails, the MCU detects that power-off protection is required and pulls down the corresponding pin voltage. At this time, the optocoupler K1 has no output, and the 2nd and 3rd pins of the first MOS tube V5 are broken, so the subsequent BMS circuit components also stop working due to the circuit break.

The utility model is applied to the power input end of the BMS of the lithium battery pack. The circuit is simple and reliable, and the original circuit needs only to be modified slightly. It can be used as long as the circuit is connected in series to the BMS power input end. Moreover, after adopting the circuit, even if the battery power is not normally shut down due to improper daily management, since an extremely high resistance of more than 10M is used between the positive and negative poles of the power supply at the input end of the circuit, its power consumption is lower than the normal self-consumption of the battery cell and can be almost ignored. Compared with before, the standby time of the battery pack can be greatly extended, and daily use and maintenance are convenient, thereby avoiding safety hazards caused by over-discharge of the battery cell, reducing battery failures caused thereby, and even increasing the cost of replacing the battery.

In the description of the present invention, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like, indicating directions and positional relationships based on the directions or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific protection scope of the present invention.

It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or are inherent to these processes, methods, products or apparatuses.

Note that the above are only preferred embodiments of the present invention and the principles of the application technology. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention is described in more detail through the above embodiments, the present invention is not limited to the specific embodiments described herein, and may include more other effective embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (6)

1. A from outage protection circuit for lithium battery BMS, its characterized in that: the circuit comprises an optical coupler K1, a power supply, a switch S1, a first MOS tube V5, a second MOS tube V8, a first resistor R75, a second resistor R76, a third resistor R77, a fourth resistor R78, a fifth resistor R89, a capacitor C71, a first diode VD28, a second diode VD29 and a third diode VD32;

The input end of the optical coupler K1 is connected with a fault triggering protection pin of the BMS, the output end of the optical coupler K1 is connected with a grid electrode of a first MOS tube V5 through a third diode VD32, the grid electrode of the first MOS tube V5 is simultaneously connected with one ends of a third resistor R77 and a fourth resistor R78, the third resistor R77 and the fourth resistor R78 form a voltage dividing circuit, the other end of the fourth resistor R78 is grounded, the other end of the third resistor R77 is sequentially grounded through a capacitor C71 and the first resistor R75, the other end of the third resistor R77 is connected with a negative electrode of a first diode VD28, and the positive electrode of the first diode VD28 is grounded; the common connection end of the capacitor C71 and the first resistor R75 is connected with the positive electrode of the power supply through the switch S1 and is also connected with the source electrode of the second MOS tube V8; the drain electrode of the first MOS tube V5 is connected with the grid electrode of the second MOS tube V8 through a fifth resistor R89, the grid electrode of the second MOS tube V8 is respectively connected with one end of a second resistor R76 and the anode of a second diode VD29, and one end of the second resistor R76 and the cathode of the second diode VD29 are simultaneously connected with the source electrode of the second MOS tube V8; the drain electrode of the second MOS tube V8 is connected with a power input circuit of the BMS.

2. The self-power-off protection circuit for a lithium battery BMS according to claim 1, wherein: and the RC circuit is formed by the first resistor R75 and the capacitor C71, wherein the value of the first resistor R75 is 10MΩ, and the value of the capacitor C71 is 0.1uF.

3. The self-power-off protection circuit for a lithium battery BMS according to claim 1, wherein: the first MOS tube V5 adopts an N-channel small-signal MOSFET 2N7000 or VN10KN to control the on-off of the second MOS tube V8.

4. The self-power-off protection circuit for a lithium battery BMS according to claim 1, wherein: the second MOS tube V8 adopts a P-channel high-current MOSFET IRF9640PBF for switching on or switching off the working power supply of the BMS main loop.

5. The self-power-off protection circuit for a lithium battery BMS according to claim 1, wherein: the device also comprises a sixth resistor R12 and a seventh resistor R13, wherein the sixth resistor R12 is connected in series between a fault triggering protection pin of the BMS and the input end of the optical coupler K1, and is used as a current limiting resistor to prevent the K1 from receiving excessive current impact and improve the circuit stability; one end of the seventh resistor R13 is connected with the output end of the optical coupler K1, the other end of the seventh resistor R13 is grounded, the resistor is used as a pull-down resistor, and the pin is clamped to be at a low level when no output exists at the output end of the K1.

6. The self-power-off protection circuit for a lithium battery BMS according to claim 1, wherein: the power supply is a 24V battery pack, and the second diode VD29 adopts an 8.2V voltage stabilizing diode.