A flexible lithium battery discharge management circuit

Abstract

The utility model discloses a nimble lithium battery discharge management circuit is applicable to single section lithium battery power supply system, and this circuit is used for when adopting the charging chip without power path management function, and the connection state of automatic switching battery and load realizes battery undervoltage protection, reverse current isolation and hysteresis judgment control. This circuit adopts two back-to-back connection's P type MOSFET control battery output path, and through comparator detects battery voltage, and through NPN / PNP triode control MOSFET's on-off state. The structure is automatically cut off battery power supply to load when external power supply is inserted, and can cut off load power supply when battery voltage is lower than the undervoltage threshold of set value, and automatically restore power supply when restoring to hysteresis upper limit. The scheme structure is simple, and parameter nimble adjustable, is applicable to the load protection and path management in various lithium battery systems.

Description

Technical Field

[0001] This utility model relates to the field of power management technology for lithium battery powered devices, specifically a flexible lithium battery discharge management circuit. In particular, it is a lithium battery charge / discharge control circuit implemented using a general-purpose comparator and discrete components, suitable for application scenarios where low-cost charging chips (such as TP4056) lack power path management functionality. Background Technology

[0002] In lithium battery power supply systems built around lithium battery cell charging chips such as TP4056, the following technical bottlenecks are often encountered:

[0003] 1. Lack of power path management function, causing the battery to continuously supply power to the load while charging;

[0004] 2. Lack of undervoltage detection mechanism, which can easily lead to battery over-discharge damage;

[0005] 3. The discharge path is not decoupled from the charging path, and there is a risk of current backflow during external power supply.

[0006] These issues reduce system efficiency and security, hindering the widespread application of this type of chip in harsh environments. Utility Model Content

[0007] The purpose of this invention is to provide a flexible lithium battery discharge management circuit suitable for charging chip scenarios that lack power path management functionality. The circuit includes a power load isolation module, a PMOS control module, a battery undervoltage detection module, an external power supply detection module, and a charging module, enabling functions such as battery undervoltage protection, external power supply insertion detection, and charge / discharge path control.

[0008] To achieve the above objectives, this utility model provides the following technical solution: a flexible lithium battery discharge management circuit, the circuit being used to connect an external power supply VCC, a battery VBAT, and a load RL, and including the following modules:

[0009] Power load isolation module: connected between the external power supply VCC and the load RL;

[0010] PMOS control module: connected between battery VBAT and load RL;

[0011] Battery undervoltage detection module: connected to battery VBAT;

[0012] External power supply detection module: connected to external power supply VCC;

[0013] Charging module: Connected between external power supply VCC and battery VBAT.

[0014] Preferably, the power load isolation module includes:

[0015] Diode D1 has its anode connected to the external power supply VCC and its cathode connected to the load RL.

[0016] Preferably, the PMOS control module includes:

[0017] Two MOSFETs Q1 and Q2 are connected back-to-back; the sources of MOSFETs Q1 and Q2 are connected to the battery VBAT and the load RL, respectively, the two drains are directly connected, and the two gates are connected to the control signal.

[0018] PNP transistor Q3, with its emitter connected to battery VBAT;

[0019] A current-limiting resistor R1 is connected between the collector of the PNP transistor Q3 and the common gate node of the MOS transistors Q1 and Q2.

[0020] Pull-down resistor R2 is connected to the common gate node of MOSFETs Q1 and Q2 and grounded;

[0021] Pull-up resistor R3 is connected at one end to battery VBAT and at the other end to the base of PNP transistor Q3.

[0022] The current-limiting resistor R8 is connected to the base of the PNP transistor Q3;

[0023] The base of the PNP transistor Q3 is connected to the battery VBAT via a pull-up resistor R3, and simultaneously connected to the output terminals of the external power supply detection module and the battery undervoltage detection module via a current-limiting resistor R8.

[0024] Preferably, the battery undervoltage detection module includes:

[0025] Voltage divider resistor R4 is connected to battery VBAT;

[0026] Voltage divider resistor R6 is connected to voltage divider resistor R4 and grounded;

[0027] Comparator U1 has its positive input terminal connected to a detection node consisting of the battery voltage divided by voltage divider resistors R4 and R6, and its negative input terminal connected to an internal reference voltage; the output type is open-drain structure, and the output control signal is sent to the PMOS control module.

[0028] The resistance ratio of the voltage divider resistors R4 and R6 is adjustable;

[0029] The comparator U1 has a fixed hysteresis.

[0030] Preferably, the external power supply detection module includes:

[0031] The current-limiting resistor R5 is connected to the external power supply VCC.

[0032] The NPN transistor Q4 has its collector connected to the PMOS control module, its emitter grounded, and its base connected to the external power supply VCC through the current-limiting resistor R5.

[0033] The grounding resistor R7 is connected between the base of the NPN transistor Q4 and ground.

[0034] Preferably, both MOS transistors Q1 and Q2 are P-type MOS transistors and are connected back-to-back in a source-to-source manner, with their gates sharing the same control potential.

[0035] The PNP transistor Q3 is a small-signal transistor for switching. Its emitter is connected to the battery VBAT, and its base is connected to the collector of the NPN transistor Q4 and the output of the comparator U1 through the current-limiting resistor R8. The collector is connected to the gate of MOSFET Q1 and MOSFET Q2 through the current-limiting resistor R1.

[0036] Preferably, the charging module includes:

[0037] The charging circuit uses a charging chip to charge the battery VBAT via an external power supply VCC; however, the charging chip does not have power path management functionality.

[0038] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0039] This invention proposes a charge / discharge management circuit for a lithium battery power supply system, suitable for charging chip scenarios that lack power path management functionality. The circuit includes a power load isolation module, a PMOS control module, a battery undervoltage detection module, an external power supply detection module, and a charging module, enabling functions such as battery undervoltage protection, external power supply insertion detection, and charge / discharge path control. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the overall structure of the charging and discharging control circuit of this utility model;

[0041] Figure 2 This is a schematic diagram of the overall circuit of this utility model;

[0042] Figure 3 This is a schematic diagram of the power load isolation module of this utility model;

[0043] Figure 4 This is a schematic diagram of the PMOS control module of this utility model;

[0044] Figure 5 This is a schematic diagram of the battery undervoltage detection module of this utility model;

[0045] Figure 6 This is a schematic diagram of the external power supply detection module of this utility model;

[0046] Figure 7 This is a schematic diagram of the charging module of this utility model; Detailed Implementation

[0047] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0048] Please see Figures 1 to 7 This utility model provides a technical solution: a flexible lithium battery discharge management circuit. The circuit is used to connect an external power supply VCC, a battery VBAT, and a load RL, and includes the following modules:

[0049] Power load isolation module: connected between the external power supply VCC and the load RL;

[0050] PMOS control module: connected between battery VBAT and load RL;

[0051] Battery undervoltage detection module: connected to battery VBAT;

[0052] External power supply detection module: connected to external power supply VCC;

[0053] Charging module: Connected between external power supply VCC and battery VBAT.

[0054] The power load isolation module includes:

[0055] Diode D1 has its anode connected to the external power supply VCC and its cathode connected to the load RL.

[0056] The PMOS control module includes:

[0057] Two MOSFETs Q1 and Q2 are connected back-to-back; the sources of MOSFETs Q1 and Q2 are connected to the battery VBAT and the load RL, respectively, the two drains are directly connected, and the two gates are connected to the control signal.

[0058] PNP transistor Q3, with its emitter connected to battery VBAT;

[0059] A current-limiting resistor R1 is connected between the collector of the PNP transistor Q3 and the common gate node of the MOS transistors Q1 and Q2.

[0060] Pull-down resistor R2 is connected to the common gate node of MOSFETs Q1 and Q2 and grounded;

[0061] Pull-up resistor R3 is connected at one end to battery VBAT and at the other end to the base of PNP transistor Q3.

[0062] The current-limiting resistor R8 is connected to the base of the PNP transistor Q3;

[0063] The base of the PNP transistor Q3 is connected to the battery VBAT via a pull-up resistor R3, and simultaneously connected to the output terminals of the external power supply detection module and the battery undervoltage detection module via a current-limiting resistor R8.

[0064] The battery undervoltage detection module includes:

[0065] Voltage divider resistor R4 is connected to battery VBAT;

[0066] Voltage divider resistor R6 is connected to voltage divider resistor R4 and grounded;

[0067] Comparator U1 has its positive input terminal connected to a detection node consisting of the battery voltage divided by voltage divider resistors R4 and R6, and its negative input terminal connected to an internal reference voltage; the output type is open-drain structure, and the output control signal is sent to the PMOS control module.

[0068] The resistance ratio of the voltage divider resistors R4 and R6 is adjustable;

[0069] The comparator U1 has a fixed hysteresis.

[0070] The external power supply detection module includes:

[0071] The current-limiting resistor R5 is connected to the external power supply VCC.

[0072] The NPN transistor Q4 has its collector connected to the PMOS control module, its emitter grounded, and its base connected to the external power supply VCC through the current-limiting resistor R5.

[0073] The grounding resistor R7 is connected between the base of the NPN transistor Q4 and ground.

[0074] Both MOS transistors Q1 and Q2 are P-type MOS transistors and are connected back-to-back in a source-to-source manner, with their gates sharing the same control potential.

[0075] The PNP transistor Q3 is a small-signal transistor for switching. Its emitter is connected to the battery VBAT, and its base is connected to the collector of the NPN transistor Q4 and the output of the comparator U1 through the current-limiting resistor R8. The collector is connected to the gate of MOSFET Q1 and MOSFET Q2 through the current-limiting resistor R1.

[0076] The charging module includes:

[0077] The charging circuit uses a charging chip to charge the battery VBAT via an external power supply VCC; however, the charging chip does not have power path management functionality.

[0078] The functions and working principles of each module in this solution are as follows:

[0079] Power load isolation module: isolates the load from the reverse current of the external power supply VCC, preventing detection errors and battery voltage backflow. Diode D1 is model SS54.

[0080] When the external power supply VCC is plugged in, its voltage is higher than the load voltage. Diode D1 is forward biased and conducts, and current flows from VCC to the load, supplying power to the load.

[0081] When powered solely by the battery, the external power supply VCC is disconnected. At this time, the voltage at the load terminal is higher than the voltage at the VCC port, and diode D1 is reverse biased and cut off, thereby cutting off the path of current flowing from the load terminal to the VCC port, achieving isolation.

[0082] External power supply detection module: detects the insertion status of external power supply VCC and outputs control signals. The NPN transistor Q4 is model S8050.

[0083] When VCC is not inserted: the base of Q4 is pulled to ground (0V) through the pull-down resistor R7, Q4 is reliably cut off, and its collector is in a high-resistance state.

[0084] When VCC is inserted: VCC provides base current to Q4 through current-limiting resistor R5, causing Q4 to saturate and conduct, and its collector voltage is pulled down to close to 0V.

[0085] Battery undervoltage detection module: detects whether the battery voltage is lower than the set undervoltage threshold and outputs a control signal. The comparator U1 is model TLV3011, which integrates a 1.242V reference voltage.

[0086] The minimum discharge voltage of a typical single lithium battery is 2.7V; resistors R4 and R6 divide the battery voltage VBAT to obtain a detection voltage, which is then sent to the positive input of comparator U1.

[0087] The negative input of comparator U1 is connected to the internal reference voltage.

[0088] When VBAT is normal (above 2.7V): the comparator U1 output is in a high-impedance state.

[0089] When VBAT is too low (below 2.7V): the internal MOSFET of comparator U1 is turned on, and the output is pulled low to ground.

[0090] The built-in hysteresis of comparator U1 can prevent the output signal from frequently changing when the battery voltage fluctuates near the threshold.

[0091] PMOS control module: Based on the control signals from the battery undervoltage detection module and the external power supply detection module, it manages the power supply path from the battery to the load; MOSFETs Q1 and Q2 are model IRF7319, and PNP transistor Q3 is model A733.

[0092] Conducting process (battery powered):

[0093] When the external power supply is not plugged in (Q4 is off) and the battery voltage is normal (U1 outputs high impedance state), the base of Q3 is pulled up to VBAT by R3, and Q3 is off.

[0094] At this time, the gate of the PMOS is pulled to ground (0V) through the pull-down resistor R2, Q1 and Q2 are turned on, and the battery supplies power to the load.

[0095] Shutdown process (external power supply or undervoltage):

[0096] When an external power source is plugged in (Q4 is turned on) or the battery is undervoltage (U1 output is pulled low), the base voltage of Q3 is pulled low, and Q3 is turned on.

[0097] After Q3 turns on, it rapidly pulls the gate voltage of the PMOS up to near VBAT through R1. At this point, the PMOS turns off, disconnecting the battery from the load.

[0098] Charging module: Provides normal charging function, charges the battery through external power supply VCC, has no power path management function, and uses the TP4056 charging chip.

[0099] When an external power source VCC is plugged in, the module is activated and charges the battery according to its own charging curve (constant current, constant voltage).

[0100] It should be noted that the initial parameters for each resistor are set as follows:

[0101] R1: 220Ω; R2: 100kΩ; R3: 220Ω; R4: 118kΩ; R5: 10kΩ; R6: 100kΩ: R7: 100kΩ; R8: 10kΩ.

[0102] The working principle of the overall circuit is as follows:

[0103] This flexible lithium battery discharge management circuit, when the external power supply VCC is inserted, pulls the base of Q4 high, turns Q4 on, and then turns on Q3 to pull the gates of the two PMOS transistors high, turning off MOS transistors Q1 and Q2. This achieves complete disconnection between the battery and the load when the external power supply VCC is inserted, with the load being powered entirely by the external power supply VCC, while preventing other charging paths from flowing to the battery. At the same time, because the outputs of comparator U1 and Q4 are both open-collector or open-drain structures, forming a logic similar to an OR gate, when Q4 is turned on, the state of the PMOS transistors is unaffected regardless of the output state of the comparator.

[0104] When the external power supply VCC is disconnected and the battery voltage is higher than the set undervoltage threshold, the comparator releases its output, the PNP transistor Q3 is turned off, and the gates of MOSFETs Q1 and Q2 are pulled down to conduct, allowing the battery to supply power to the load. When the battery voltage drops below 2.7V, the comparator U1 output is pulled low, which in turn pulls down the base of the PNP transistor Q3, turning it on. The gates of MOSFETs Q1 and Q2 are pulled high to VBAT, turning off the MOSFETs and thus cutting off the discharge path, completing the undervoltage protection.

[0105] The circuit structure of this invention does not require the participation of an MCU, the components are universal and the configuration is flexible, and it is suitable for various scenarios that require battery protection and power supply path control, such as Bluetooth headsets, wearable devices, portable terminals, and IoT modules.

[0106] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flexible lithium battery discharge management circuit, characterized in that: The circuit is used to connect the external power supply VCC, the battery VBAT, and the load RL, and includes the following modules: Power load isolation module: connected between the external power supply VCC and the load RL; PMOS control module: connected between battery VBAT and load RL; Battery undervoltage detection module: connected to battery VBAT; External power supply detection module: connected to external power supply VCC; Charging module: Connected between external power supply VCC and battery VBAT.

2. The flexible lithium battery discharge management circuit according to claim 1, characterized in that: The power load isolation module includes: Diode D1 has its anode connected to the external power supply VCC and its cathode connected to the load RL.

3. The flexible lithium battery discharge management circuit according to claim 1, characterized in that: The PMOS control module includes: Two MOSFETs Q1 and Q2 are connected back-to-back; the sources of MOSFETs Q1 and Q2 are connected to the battery VBAT and the load RL, respectively, the two drains are directly connected, and the two gates are connected to the control signal. PNP transistor Q3, with its emitter connected to battery VBAT; A current-limiting resistor R1 is connected between the collector of the PNP transistor Q3 and the common gate node of the MOS transistors Q1 and Q2. Pull-down resistor R2 is connected to the common gate node of MOSFETs Q1 and Q2 and grounded; Pull-up resistor R3 is connected at one end to battery VBAT and at the other end to the base of PNP transistor Q3. The current-limiting resistor R8 is connected to the base of the PNP transistor Q3; The base of the PNP transistor Q3 is connected to the battery VBAT via a pull-up resistor R3, and simultaneously connected to the output terminals of the external power supply detection module and the battery undervoltage detection module via a current-limiting resistor R8.

4. The flexible lithium battery discharge management circuit according to claim 1, characterized in that: The battery undervoltage detection module includes: Voltage divider resistor R4 is connected to battery VBAT; Voltage divider resistor R6 is connected to voltage divider resistor R4 and grounded; Comparator U1 has its positive input terminal connected to a detection node consisting of the battery voltage divided by voltage divider resistors R4 and R6, and its negative input terminal connected to an internal reference voltage; the output type is open-drain structure, and the output control signal is sent to the PMOS control module. The resistance ratio of the voltage divider resistors R4 and R6 is adjustable; The comparator U1 has a fixed hysteresis.

5. The flexible lithium battery discharge management circuit according to claim 1, characterized in that: The external power supply detection module includes: The current-limiting resistor R5 is connected to the external power supply VCC. The NPN transistor Q4 has its collector connected to the PMOS control module, its emitter grounded, and its base connected to the external power supply VCC through the current-limiting resistor R5. The grounding resistor R7 is connected between the base of the NPN transistor Q4 and ground.

6. The flexible lithium battery discharge management circuit according to claim 3, characterized in that: Both MOS transistors Q1 and Q2 are P-type MOS transistors and are connected back-to-back in a source-to-source manner, with their gates sharing the same control potential. The PNP transistor Q3 is a small-signal transistor for switching. Its emitter is connected to the battery VBAT, and its base is connected to the collector of the NPN transistor Q4 and the output of the comparator U1 through the current-limiting resistor R8. The collector is connected to the gate of MOSFET Q1 and MOSFET Q2 through the current-limiting resistor R1.

7. A flexible lithium battery discharge management circuit according to claim 1, characterized in that: The charging module includes: The charging circuit uses a charging chip to charge the battery VBAT via an external power supply VCC; however, the charging chip does not have power path management functionality.

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