An electric energy meter power supply system and a protection circuit for a charging battery thereof

Abstract

This invention relates to a power supply system for an electricity meter and its rechargeable battery protection circuit, belonging to the field of power protection technology. The invention integrates an anti-backflow unit within the step-down conversion module to prevent current from the rechargeable battery from flowing back into the power input module, thereby reducing capacitor ineffective losses. It also integrates a current-limiting unit and a first unidirectional conduction unit within the charging control module. The current-limiting unit restricts the charging current flowing to the rechargeable battery, while the first unidirectional conduction unit ensures that the charging current flows unidirectionally to the rechargeable battery. The current-limiting unit controls the charging current through its own resistance characteristics, avoiding damage to the battery from abnormal current (too high / too low). The first unidirectional conduction unit ensures that the charging current flows unidirectionally to the battery, preventing reverse current from flowing into the circuit during battery discharge, achieving a balance between "efficient charging + battery protection," thereby improving circuit reliability and battery lifespan.

Description

Technical Field

[0001] This invention relates to a power supply system for an electricity meter and its rechargeable battery protection circuit, belonging to the field of power protection technology. Background Technology

[0002] In electronic devices such as three-phase energy meters and communication modules, rechargeable batteries are typically required as backup power sources to meet emergency power needs when the main power supply (e.g., 12V) is interrupted. For example, Chinese patent application CN112636454A discloses a novel energy meter power supply circuit and energy meter. The circuit includes a main power supply module and a backup power supply module. The first output terminal of the main power supply module is connected to the power supply terminal of the energy meter's processing module, the second output terminal of the main power supply module is connected to the charging terminal of the backup power supply module, and the output terminal of the backup power supply module is connected to the power supply terminal of the energy meter's processing module. The main power supply module supplies power to the processing module and charges the backup power supply module; the backup power supply module supplies power to the processing module when the main power supply module is interrupted. However, existing rechargeable battery circuits have the following technical drawbacks: 1. Current backflow problem: After the main power supply (12V) is disconnected, the battery current is easy to backflow to the main power supply pin through the internal MOSFET and parallel diode of the step-down chip, resulting in the unexplained loss of battery power and affecting the backup power supply time; 2. Uncontrolled charging current: The lack of a precise current limiting mechanism means that excessively high charging current (such as exceeding 60mA for fast charging) can shorten battery life, while excessively low current can lead to low charging efficiency. 3. Excessive voltage drop: When using backup power, the forward voltage drop of the diode is too high (e.g., the voltage drop of a conventional diode > 0.7V), which causes a significant decrease in the battery output voltage and affects the normal operation of backend loads such as 5G modules and MCUs; 4. Insufficient output voltage accuracy: The output voltage of the buck module relies on resistor feedback adjustment, but the resistor selection does not take into account error control, which can easily cause the output voltage to exceed the load tolerance range (e.g., >5.5V), leading to load failure. Summary of the Invention

[0003] The purpose of this invention is to provide a power supply system for an electricity meter and its rechargeable battery protection circuit, so as to solve the problems of reverse current in the rechargeable battery and uncontrolled charging current in the current power supply system for electricity meters.

[0004] To solve the above-mentioned technical problems, the present invention provides a rechargeable battery protection circuit for an electricity meter power supply system. The protection circuit includes a step-down converter module, a charging control module, and a rechargeable battery. The input terminal of the step-down converter module is used to connect to an external power source, the output terminal of the step-down converter module is connected to the input terminal of the charging control module, the output terminal of the charging control module is connected to the rechargeable battery to charge the rechargeable battery, and the output terminal of the rechargeable battery is used to connect to an external load to supply power to the external load. The step-down converter module integrates an anti-backflow unit to prevent the current from the rechargeable battery from flowing back to the external power source; the charging control module is equipped with a current limiting unit and a first unidirectional conduction unit. The current limiting unit is used to limit the charging current flowing from the charging control module to the rechargeable battery, and the first unidirectional conduction unit is used to ensure that the charging current flows unidirectionally to the rechargeable battery.

[0005] Furthermore, the buck converter module uses a high-frequency synchronous rectification buck switching mode converter as the core chip. The output pin of the converter is also connected to a feedback regulation module, which is used to regulate the output voltage of the converter so that the converter outputs a stable target voltage.

[0006] Furthermore, the backflow prevention unit employs a first diode, the anode of which is connected to an external power supply, and the cathode of which is connected to the input pin of the converter.

[0007] Furthermore, the current limiting unit adopts a current limiting resistor, the first unidirectional conduction unit adopts a second diode, one end of the current limiting resistor is connected to the output terminal of the buck converter module, the other end of the current limiting resistor is connected to the anode of the second diode, and the cathode of the second diode is connected to the positive terminal of the rechargeable battery.

[0008] Furthermore, the output terminal of the rechargeable battery is connected to an external load through a second unidirectional conduction unit. The second unidirectional conduction unit uses a third diode, the anode of which is connected to the positive terminal of the rechargeable battery, and the cathode of which is connected to the external load, serving as the output terminal of the power supply system.

[0009] Furthermore, the feedback adjustment module includes two feedback resistors connected in series. The output pin of the converter is grounded through the two feedback resistors connected in series, and the connection point of the two feedback resistors connected in series is connected to the feedback pin of the converter.

[0010] Furthermore, the enable pin of the converter is connected to an external power supply via a pull-up resistor.

[0011] Furthermore, the buck converter module also includes a boot circuit unit, which includes a boot resistor and a boot capacitor. One end of the boot resistor is connected to the bootstrap pin of the converter, and the other end of the boot resistor is connected to the output pin of the converter through the boot capacitor.

[0012] Furthermore, the input pins of the converter are connected in parallel with decoupling capacitors, the VCC pins of the converter are connected in parallel with decoupling capacitors, and the AAM pins of the converter are grounded through a resistor.

[0013] The present invention also provides a power supply system for an electricity meter, including a power input module and a rechargeable battery protection circuit. The power input module is used to provide external power to the rechargeable battery protection circuit. The rechargeable battery protection circuit adopts the rechargeable battery protection circuit of the power supply system of the present invention, including a step-down conversion module, a charging control module and a rechargeable battery. The input terminal of the step-down conversion module is connected to the power input module, the output terminal of the step-down conversion module is connected to the input terminal of the charging control module, the output terminal of the charging control module is connected to the rechargeable battery to charge the rechargeable battery, and the output terminal of the rechargeable battery is used to connect to an external load to supply power to the external load. The step-down converter module integrates an anti-backflow unit to prevent the current from the rechargeable battery from flowing back into the power input module; the charging control module is equipped with a current limiting unit and a first unidirectional conduction unit. The current limiting unit is used to limit the charging current flowing from the charging control module to the rechargeable battery, and the first unidirectional conduction unit is used to ensure that the charging current flows unidirectionally to the rechargeable battery.

[0014] Furthermore, the buck converter module uses a high-frequency synchronous rectification buck switching mode converter as the core chip. The output pin of the converter is also connected to a feedback regulation module, which is used to regulate the output voltage of the converter so that the converter outputs a stable target voltage.

[0015] Furthermore, the backflow prevention unit employs a first diode, the anode of which is connected to an external power supply, and the cathode of which is connected to the input pin of the converter.

[0016] Furthermore, the current limiting unit adopts a current limiting resistor, the first unidirectional conduction unit adopts a second diode, one end of the current limiting resistor is connected to the output terminal of the buck converter module, the other end of the current limiting resistor is connected to the anode of the second diode, and the cathode of the second diode is connected to the positive terminal of the rechargeable battery.

[0017] Furthermore, the output terminal of the rechargeable battery is connected to an external load through a second unidirectional conduction unit. The second unidirectional conduction unit uses a third diode, the anode of which is connected to the positive terminal of the rechargeable battery, and the cathode of which is connected to the external load, serving as the output terminal of the power supply system.

[0018] Furthermore, the feedback adjustment module includes two feedback resistors connected in series. The output pin of the converter is grounded through the two feedback resistors connected in series, and the connection point of the two feedback resistors connected in series is connected to the feedback pin of the converter.

[0019] Furthermore, the enable pin of the converter is connected to an external power supply via a pull-up resistor.

[0020] Furthermore, the buck converter module also includes a boot circuit unit, which includes a boot resistor and a boot capacitor. One end of the boot resistor is connected to the bootstrap pin of the converter, and the other end of the boot resistor is connected to the output pin of the converter through the boot capacitor.

[0021] Furthermore, the input pins of the converter are connected in parallel with decoupling capacitors, the VCC pins of the converter are connected in parallel with decoupling capacitors, and the AAM pins of the converter are grounded through a resistor.

[0022] The beneficial effects of this invention are as follows: This invention integrates an anti-backflow unit within the step-down conversion module to prevent current from the rechargeable battery from flowing back into the power input module, thereby reducing capacitor ineffective losses. It also integrates a current-limiting unit and a first unidirectional conduction unit within the charging control module. The current-limiting unit limits the charging current flowing to the rechargeable battery, and the first unidirectional conduction unit ensures that the charging current flows unidirectionally to the rechargeable battery. The current-limiting unit controls the charging current through its own resistance characteristics, avoiding damage to the battery from abnormal current (too high / too low). The first unidirectional conduction unit ensures that the charging current flows unidirectionally to the battery, preventing reverse current flow into the circuit during battery discharge, achieving a balance between "efficient charging + battery protection," thereby improving circuit reliability and battery lifespan. Attached Figure Description

[0023] Figure 1 This is a circuit diagram of the power supply system for the electricity meter of the present invention. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0025] Implementation of Power Supply System for Electricity Meters The power supply system for the electricity meter of this invention includes a power input module, a step-down conversion module, a charging control module, and a battery power supply module (also called a rechargeable battery, generally a nickel-metal hydride battery). The output terminal of the power input module is electrically connected to the input terminal of the step-down conversion module to provide a 12V input voltage to the step-down conversion module. The output terminal of the step-down conversion module is electrically connected to the input terminal of the charging control module. The output terminal of the charging control module is electrically connected to the positive terminal of the rechargeable battery, and the negative terminal of the rechargeable battery is grounded. The positive terminal of the rechargeable battery is also electrically connected to the input terminal of the battery power supply module, and the output terminal of the battery power supply module is used to connect to an external load. The step-down conversion module integrates an anti-backflow unit to prevent current from the rechargeable battery from flowing back to the power input module. The charging control module integrates a current limiting unit and a first unidirectional conduction unit. The current limiting unit limits the charging current flowing to the rechargeable battery, and the first unidirectional conduction unit ensures that the charging current flows unidirectionally to the rechargeable battery. In addition, a feedback adjustment module is provided. The output of the buck converter module is divided into two paths: one path is electrically connected to the input of the feedback adjustment module, and the other path is electrically connected to the input of the charging control module. The feedback adjustment module is used to adjust the output voltage of the buck converter module so that the buck converter module outputs a stable target voltage VCC.

[0026] This invention achieves a complete power supply and charging closed loop through the coordinated connection and functional design of five major modules: power input, step-down conversion, charging control, battery power supply, and feedback regulation. This is accomplished when the main power supply is normal, providing step-down power supply (for the downstream load) and battery charging, as well as backup battery power supply when the main power supply is disconnected. The step-down conversion module's anti-backflow unit blocks the reverse flow of battery current to the main power supply, preventing ineffective battery power loss. The charging control module's current limiting and unidirectional conduction design ensures the correct direction of the charging current and prevents abnormal charging current from affecting battery life. The feedback regulation module stabilizes the step-down conversion output voltage, ensuring that the output voltage matches the load requirements, thus improving the overall circuit power supply reliability, battery utilization efficiency, and load adaptability.

[0027] Specifically, the core chip of the buck converter module of this invention is a high-frequency synchronous rectification buck switching mode converter. The high-frequency synchronous rectification buck switching mode converter has a built-in power MOSFET, a synchronous frequency range of 0.2 to 2 MHz, and a maximum output current of 3 A. The high-frequency operating characteristics of the high-frequency synchronous rectification buck switching mode converter can improve power conversion efficiency and reduce energy loss during the conversion process. The built-in power MOSFET eliminates the need for additional external power devices, simplifying the circuit structure, reducing the number of external components, and lowering circuit complexity and space occupation. The specific output current capability can meet the power supply requirements of multiple downstream loads (such as remote 5G module power conversion chips and main control MCU voltage regulator chips), avoiding load power interruption or abnormal operation due to insufficient current, and ensuring stable operation of the load. The high-frequency synchronous rectification buck switch-mode converter in this embodiment uses the MP2315 series chip. This series of chips is a mature commercial model, and its performance has been market-proven, ensuring the stability and reliability of the buck conversion function. The industrial-grade design of the MP2315 series chip is adapted to complex operating conditions (such as voltage fluctuations and ambient temperature changes) in three-phase energy meters, communication modules, etc., reducing circuit failures caused by insufficient chip performance. At the same time, the versatility of this series of chips facilitates subsequent circuit debugging, maintenance, and mass production, reducing the R&D cycle and production costs. As other embodiments, other similar voltage regulator chips can also be used.

[0028] In this embodiment, the backflow prevention unit is a first diode D1. The anode of the first diode D1 is electrically connected to the output terminal of the power input module, and the cathode of the first diode is electrically connected to the VIN pin (input pin) of the buck converter module. The first diode is model RB160M-60TR, and the package type is SOD-123. The backflow prevention unit uses a first diode D1 with a specific connection method. Utilizing the unidirectional conduction characteristic of the diode, it can effectively block the backflow path of the rechargeable battery current to the power input module (such as the 12V power supply pin of the energy meter), avoiding the uninterrupted loss of battery power when the main power supply is disconnected, and extending the battery backup power supply time. The specific package type of the diode adapts to the miniaturization design requirements of the circuit, meets the compact requirements of the internal space of electronic devices, and at the same time ensures the installation stability and electrical connection reliability of the diode in the circuit.

[0029] Specifically, in this embodiment, the current limiting unit is a current limiting resistor R2, and the first unidirectional conduction unit is a second diode D2; one end of the current limiting resistor R2 is electrically connected to the output terminal of the buck converter module, the other end of the current limiting resistor R2 is electrically connected to the anode of the second diode D2, and the cathode of the second diode D2 is electrically connected to the positive terminal of the rechargeable battery; the current limiting resistor R2 is of type RC-1206-100Ω-1 / 4W±1%±50ppm, the second diode D2 is of type 1N4148W, and the package type is SOD-123; the charging current limited by the current limiting resistor R2 is 45mA. The current-limiting resistor controls the charging current flowing to the battery through its own resistance characteristics, preventing excessive current from causing battery overheating and shortening its lifespan, or insufficient current from causing low charging efficiency, thus achieving balanced battery charging and extending battery life. The unidirectional conduction characteristic of the second diode D2 ensures that the charging current flows only from the buck converter module to the battery, preventing the current from flowing back into the charging control module when the battery is discharging, avoiding damage to circuit components and waste of battery power. The compatible component models and packages ensure that the charging control module works stably under different operating conditions, improving the safety and reliability of the charging process.

[0030] Specifically, in this embodiment, the battery power supply module integrates a second unidirectional conduction unit, which is a third diode D3; the anode of the third diode D3 is electrically connected to the positive terminal of the rechargeable battery, and the cathode of the third diode D3 serves as the output terminal of the battery power supply module; the third diode D3 is model RB160M-60TR, packaged in SOD-123 form, with a forward rectified current of not less than 1A and a forward voltage drop of not more than 0.4V.

[0031] The unidirectional conduction characteristic of the second diode prevents the current from the buck converter module from flowing into the battery through the battery power supply module when the main power supply is normal, thus avoiding overcharging of the battery and protecting its performance. The smaller forward voltage drop reduces voltage decay when the battery is powered, ensuring that the downstream load can still obtain a stable voltage in the backup power supply mode, and ensuring the normal operation of the load. Sufficient forward rectified current capability adapts to the maximum discharge demand of the battery, preventing the diode from being damaged due to insufficient current carrying capacity, ensuring uninterrupted backup power supply, and improving the reliability and continuity of backup power supply.

[0032] Specifically, in this embodiment, the feedback adjustment module includes a feedback resistor R6 and a feedback resistor R10; one end of the feedback resistor R6 is electrically connected to the output terminal of the buck converter module, and the other end of the feedback resistor R6 is electrically connected to the FB pin of the buck converter module, and also electrically connected to one end of the feedback resistor R10; the other end of the feedback resistor R10 is grounded; the model of the feedback resistor R6 is RC-0603-6.8kΩ-1 / 10W±1%±100ppm, and the model of the feedback resistor R10 is RC-0603-1.2kΩ-1 / 10W±1%±100ppm; the calculation formula for the target voltage VCC is VCC=(R6 / R10+1)×0.8, and VCC<5.5V, and the specific value of the target voltage VCC is 5.33V. Two feedback resistors precisely regulate the output voltage of the buck converter module through voltage division, stabilizing the output voltage within the range required by the load and battery charging. This prevents damage to the load or battery due to excessively high voltage, or abnormal load operation and low charging efficiency due to excessively low voltage. The parameter compatibility of the resistors ensures accurate voltage division ratio, reducing output voltage fluctuations caused by resistor errors. This provides a stable voltage foundation for power supply to the downstream load and battery charging, improving the overall power supply accuracy and stability of the circuit.

[0033] Specifically, in this embodiment, the buck converter module also includes an enable control unit, which is a pull-up resistor R4. One end of the pull-up resistor R4 is electrically connected to the output terminal of the power input module, and the other end of the pull-up resistor R4 is electrically connected to the EN / SYNC pin of the buck converter module. The pull-up resistor R4 is of type RC-0603-100kΩ-1 / 10W±5%±100ppm, used to keep the buck converter module in a continuous power conversion working state. The pull-up resistor pulls the voltage of the EN / SYNC pin to the power input voltage level, so that the buck converter module can be continuously in a working state without additional control signals. This ensures that when the main power supply is normal, the power supply to the downstream load and battery charging are uninterrupted, ensuring the continuity of circuit function. The appropriate resistor type ensures stable pull-up current and avoids abnormal EN / SYNC pin signals due to improper resistor values, thereby preventing frequent start-stop of the buck converter module and improving the stability and reliability of circuit operation.

[0034] Specifically, in this embodiment, the buck converter module further includes a pilot circuit unit, which consists of a pilot resistor R1 and a pilot capacitor C3. One end of the pilot resistor is electrically connected to the BST pin of the buck converter module, and the other end of the pilot resistor R1 is electrically connected to the SW pin of the buck converter module. The pilot capacitor is connected in series across the two ends of the pilot resistor. The pilot resistor is RC-0603-20Ω-1 / 10W±5%±100ppm, and the pilot capacitor is RC-0603-100nF / 50V±10% / X7R. The pilot circuit, composed of the pilot resistor and capacitor, provides a stable floating power supply to the high-side switch driver of the buck converter module, ensuring normal on and off of the high-side switch and avoiding a decrease in buck conversion efficiency or chip damage due to unstable driver power supply. The energy storage function of the capacitor and the current limiting function of the resistor work together to reduce voltage fluctuations during driver operation, improve the stability of the buck conversion process, and ensure that the buck converter module continuously outputs a stable voltage to meet the load and charging requirements.

[0035] Specifically, in this embodiment, the rechargeable battery is a 4.8V / 300mAh nickel-metal hydride battery with a maximum discharge current of not less than 900mA; the external load includes the input terminal of the power conversion chip of the remote 5G module and the input terminal of the voltage regulator chip of the main control MCU; the 12V input voltage of the power input module is obtained from pins 1 and 2 of the three-phase energy meter and the low-voltage interface of the communication module. The characteristics of the nickel-metal hydride battery are adapted to the backup power supply requirements, providing a stable discharge voltage and sufficient backup power supply time, ensuring that the back-end load can still work normally after the main power supply is disconnected; the clear load type (power conversion chip of the remote 5G module, voltage regulator chip of the main control MCU) allows the circuit design to be specifically adapted to the actual application scenario, avoiding power supply problems caused by improper load matching, and ensuring the reliable operation of loads with high power consumption or high stability requirements; the specific power input source (three-phase energy meter, low-voltage interface of the communication module) allows the circuit to conveniently obtain the main power supply without an additional power supply interface, improving the compatibility and practicality of the circuit with existing equipment.

[0036] Specifically, in this embodiment, a decoupling capacitor C1 is connected in parallel at the input terminal of the buck converter module. The decoupling capacitor C1 is an ESR capacitor with a capacitance of 22μF. A decoupling capacitor Cvcc is also connected in parallel at the VCC pin of the buck converter module. The decoupling capacitor Cvcc is of type RC-0603-100nF / 50V±10% / X7R. The AAM pin (Advanced Asynchronous Modulation, also known as the light load efficiency enhancement mode control pin) of the buck converter module is also grounded through a resistor R9. The resistor R9 is of type RC-0603-100kΩ-1 / 10W±5%±100ppm, which is used to set the buck converter module to asynchronous mode when the load is low. The ESR decoupling capacitor alleviates the problem of discontinuous input current in the buck converter at the power input terminal, stabilizes the input voltage, reduces the impact of voltage fluctuations on buck conversion, and improves conversion efficiency. The decoupling capacitor filters out high-frequency noise from the VCC pin, providing a clean bias voltage for the buck converter module, ensuring stable operation of the internal circuitry of the chip, and reducing chip performance abnormalities caused by noise interference. The grounding resistor of the AAM pin sets the module to asynchronous mode when the load is small, adapting to light load conditions, reducing energy loss under light load, and improving the adaptability and energy utilization efficiency of the circuit under different load conditions.

[0037] In summary, the power supply system circuit provided in this embodiment achieves automatic switching between two operating conditions through the coordinated operation of its various modules: "power supply + charging when the main power supply is normal" and "backup power supply when the main power supply is disconnected." The principle is based on the logic of "voltage conversion + unidirectional conduction + precise adjustment," as detailed below: 1. Core module collaboration relationships The circuit uses a "step-down converter module" as its core hub. The power input module provides it with a 12V main power supply, the feedback regulation module provides it with closed-loop control of the output voltage, and the charging control module and battery power supply module respectively realize the functions of "battery charging" and "backup power supply". Each module is electrically connected to key components (diodes, resistors, capacitors) through wires to form a complete working link.

[0038] 2. Operating procedure when the main power supply (12V) is normal Power Input and Buck Conversion: The power input module obtains 12V main power from the three-phase energy meter and the low-voltage interface of the communication module, and transmits it to the input terminal of the buck converter module; the core chip of the buck converter module (such as the MP2315 series) works continuously under the action of the pull-up resistor at the enable terminal, and steps down the 12V voltage to a stable target voltage; at the same time, the decoupling capacitor at the input terminal solves the problem of discontinuous input current of the buck converter, and the decoupling capacitor of the bias pin filters out noise, ensuring stable buck conversion; Two-way output distribution: The stable voltage output from the buck converter module is divided into two paths: The first power supply directly powers the external load (the input of the remote 5G module power conversion chip and the input of the main control MCU voltage regulator chip), meeting the voltage requirements for normal operation of the load; The second path transmits to the charging control module. After the charging current is limited by the current-limiting resistor and the current is ensured to be unidirectional by the second diode, the current flows to the nickel-metal hydride battery to achieve stable charging of the battery. Backup module cutoff: At this time, the third diode in the battery power supply module is cut off due to reverse bias, which prevents the current of the buck converter module from being diverted to the battery through the battery power supply module and prevents the battery from being overcharged.

[0039] 3. Operating procedure when main power supply (12V) is disconnected The buck converter stops working: After the main power supply is disconnected, the buck converter stops buck conversion and output due to the lack of input voltage. The charging control module has no current input, and the battery charging process is interrupted. Backflow protection activation: The first diode in the step-down converter module is turned off due to reverse bias, blocking the backflow path of battery current to the power input module (such as the 12V pin of the energy meter) and avoiding battery power loss; Backup power supply switching: The nickel-metal hydride battery serves as a backup power source, discharging to the external load through the third diode in the battery power supply module; the low forward voltage drop characteristic of the third diode reduces voltage decay, ensuring that the load receives a stable voltage, realizing the backup power supply function, and ensuring that the load does not work uninterrupted.

[0040] How to use This system is designed for "plug and play + automatic operation" and requires no complex manual operation. The specific usage method, combined with its application scenario and circuit connection logic, is as follows: 1. Circuit connection steps Power input connection: Connect the output terminal of the circuit's "power input module" to the corresponding low-voltage interface (pins 1 and 2) of the three-phase energy meter and the communication module to ensure that the 12V main power supply is stably input to the step-down conversion module; Load connection: Connect the output terminal of the circuit's "battery power module" to the corresponding external load (the input terminal of the power conversion chip of the remote 5G module and the input terminal of the voltage regulator chip of the main control MCU) to ensure that the load can receive the voltage of the main power supply or the backup power supply; Battery connection: Connect the positive terminal of the nickel-metal hydride battery to the output terminal of the "charging control module" and the input terminal of the "battery power supply module" respectively, and ground the negative terminal of the battery to ensure that the battery can receive charging current and output discharging current when the power is off; No additional debugging required: The core components of the circuit (such as current-limiting resistors, feedback resistors, and diodes) have been selected and adapted according to the parameters. After the connection is completed, there is no need to adjust the resistors, switches, or other components. The circuit can automatically enter the working state.

[0041] 2. Daily Operation and Maintenance Automatic working mode: When the main power supply is normal, the circuit automatically realizes "load power supply + battery charging" without manual intervention; when the main power supply is disconnected, the circuit automatically switches to "battery backup power supply" until the main power supply is restored or the battery is depleted. Status observation (optional): The output voltage of the step-down converter module and the battery charging current can be monitored by external testing equipment (such as a multimeter) to confirm whether the circuit is working properly (no need to disassemble the circuit); Battery maintenance: Since the circuit has achieved precise charging and overcharge protection, there is no need to replace the battery frequently. Just check the battery connection regularly according to the battery's normal life cycle (in combination with the frequency of device use) to avoid the failure of backup power supply due to loose connection.

[0042] In summary, the component selection and circuit design of each module in this rechargeable battery protection circuit are as follows: 1. Power input module Functional purpose: to provide the 12V main power supply voltage (denoted as VCC12V) for the entire circuit.

[0043] Voltage acquisition path: Power is obtained from the low-voltage interface (pins 1 and 2) of the three-phase energy meter and the communication module.

[0044] Circuit structure: There are no additional active electronic components. The circuit is directly connected to the VIN pin of the buck converter module through a wire to realize the transmission of 12V voltage to the buck converter module.

[0045] 2. Step-down converter module Core chip: The MP2315GJ high-frequency synchronous rectification buck switching converter is used. It has a built-in power MOSFET, a synchronous frequency range of 0.2 to 2 MHz, and a maximum output current of 3 A. It undertakes the core function of 12V voltage buck conversion.

[0046] Key auxiliary unit design: Anti-backflow unit: Configured with a first diode D1 (model RB160M-60TR, package SOD-123), whose anode is electrically connected to the output terminal of the power input module and the cathode is electrically connected to the SW pin of MP2315GJ, blocking the backflow path of the rechargeable battery current to the power input module (12V power supply pin of the energy meter).

[0047] Enable control unit: Set pull-up resistor R4 (model RC-0603-100kΩ-1 / 10W±5%±100ppm), one end connected to VCC12V, the other end connected to the EN / SYNC pin of MP2315GJ. The pull-up voltage keeps the chip in power conversion operation state without additional control signals.

[0048] The pilot circuit unit consists of a pilot resistor (model RC-0603-20Ω-1 / 10W±5%±100ppm) and a pilot capacitor (model RC-0603-100nF / 50V±10% / X7R) connected in parallel between the BST and SW pins of the MP2315GJ to form a floating power supply for the high-side switch driver, ensuring stable on / off of the high-side switch.

[0049] Decoupling and decoupling unit: A 22μF FES R decoupling capacitor C1 is connected in parallel at the module input to solve the problem of discontinuous input current of the buck converter, maintain the stability of DC input voltage and provide AC current; a 0.1μF decoupling capacitor (model RC-0603-100nF / 50V±10% / X7R) is connected in parallel at VCC (bias pin) of MP2315GJ to filter out high-frequency noise and ensure the purity of chip bias voltage.

[0050] Mode control unit: The AAM pin of MP2315GJ is grounded through resistor R9 (model RC-0603-100kΩ-1 / 10W±5%±100ppm). When the load is small, the chip is set to asynchronous mode to adapt to light load conditions and reduce energy loss.

[0051] 3. Charging control module Functional purpose: To provide a stable charging current to the nickel-metal hydride battery when the main power supply is normal, and to ensure the correct charging direction.

[0052] Core components and parameters: Current limiting unit: The current limiting resistor R2 (model RC-1206-100Ω-1 / 4W±1%±50ppm) is used to limit the charging current to 45mA through the resistance characteristics (between the standard charging current of 30mA and the fast charging current of 60mA for NiMH batteries, taking into account both charging efficiency and battery life).

[0053] Unidirectional conduction unit: A second diode D2 (model 1N4148W, package type SOD-123) is configured, with its anode electrically connected to the current-limiting resistor R2 and its cathode electrically connected to the positive terminal of the rechargeable battery; by utilizing the unidirectional conduction characteristic of the diode, the charging current is ensured to flow only from the buck converter module to the battery, avoiding the current flowing back into the charging control module when the battery is discharging.

[0054] Parameter design basis: When the output voltage VCC of the buck converter module is 5.33V, the voltage drop of 1N4148W at 45mA current is 0.8V, and the voltage across R2 is 4.53V. According to Ohm's law, the maximum required value of R2 is about 100.67Ω. A 100Ω standard resistor is selected, and the resistor power (about 0.2025W) meets the tolerance requirements of 1 / 4W package.

[0055] 4. Battery power supply module Battery selection: Use 4.8V / 300mAh nickel-metal hydride batteries (denoted as BATI), with a maximum discharge current of 900mA, as backup power when the main power supply is disconnected.

[0056] Unidirectional conduction and low voltage drop design: A third diode D3 (model RB160M-60TR, package SOD-123) is configured, with its anode electrically connected to the positive terminal of the battery and its cathode serving as the module output terminal (electrically connected to the external load). The forward rectified current of this diode is 1A (meeting the maximum discharge requirements of the battery), and the forward voltage drop is only 0.4V. This not only prevents the current from flowing back into the battery when the main power supply is normal (avoiding overcharging), but also reduces the voltage attenuation during backup power supply, ensuring the stability of the load voltage.

[0057] 5. Feedback Adjustment Module Functional positioning: Precisely adjust the output voltage of the buck converter module to ensure that the output voltage is stable at the target value (VCC < 5.5V), adapting to the power supply and battery charging needs of the load.

[0058] Core components and connections: A voltage divider circuit is formed by feedback resistors R6 and R10; R6 is model RC-0603-6.8kΩ-1 / 10W±1%±100ppm, one end is connected to the output terminal of the step-down converter module, and the other end is connected to the FB pin of MP2315GJ and one end of R10; R10 is model RC-0603-1.2kΩ-1 / 10W±1%±100ppm, and the other end is grounded.

[0059] Voltage calculation logic: According to the MP2315GJ output voltage formula VCC=(R6 / R10+1)×0.8, substituting the parameters of R6 and R10, VCC=5.33V (<5.5V) is calculated. Moreover, the power flowing through the two resistors is <1 / 10W, which meets the component withstand requirements and achieves precise control of the output voltage.

[0060] Circuit operation process 1. When the main power supply (12V) is normal The power input module transmits 12V voltage to the buck converter module. The MP2315GJ continues to operate under the action of the EN / SYNC pin high level (pull-up by R4), bucking the 12V to 5.33V (VCC).

[0061] After step-down, VCC is output in two ways: one way directly supplies power to the external load (the input of the remote 5G module power conversion chip and the input of the main control MCU voltage regulator chip); the other way charges the 4.8V / 300mAh NiMH battery through the charging control module (R2 current limiting, D2 unidirectional conduction), with the charging current stabilizing at 45mA.

[0062] The D3 circuit of the battery-powered module is cut off due to reverse bias, preventing VCC from being shunted through the battery-powered module.

[0063] 2. When the main power supply (12V) is disconnected The step-down converter module stopped working due to lack of input voltage, the charging control module had no current output, and the charging process was interrupted.

[0064] The D1 pin of the buck converter is reverse biased and cut off to prevent battery current from flowing back to the power input module (12V pin of the energy meter) and avoid battery power loss.

[0065] The nickel-metal hydride battery discharges to the external load through D3 of the battery power supply module. The low voltage drop characteristic of D3 ensures that the load obtains a stable voltage, realizing the backup power supply function.

[0066] It is evident that the power supply system of the present invention has the following effects: 1. Anti-backflow protection to reduce battery power loss: The step-down converter module has a built-in first diode (D1), which uses the unidirectional conduction characteristic of the diode to block the current backflow path from the rechargeable battery to the power input module (such as the 12V pin of the energy meter), so as to avoid the battery power being wasted when the main power supply is disconnected and extend the backup power supply time. 2. Precise charging, balancing efficiency and battery life: The charging control module is equipped with a current-limiting resistor and a second diode. The current-limiting resistor controls the charging current through its own resistance characteristics to avoid damage to the battery due to abnormal current (too high / too low). The second diode ensures that the charging current flows unidirectionally to the battery and prevents the current from flowing back into the circuit when the battery is discharging, thus achieving a balance between "efficient charging and battery protection". 3. Low voltage drop backup power supply to ensure stable load operation: The battery power supply module adopts a third diode with low forward voltage drop to reduce voltage attenuation when the battery is in backup power supply mode, ensuring that the back-end load (remote 5G module power conversion chip, main control MCU voltage regulator chip) can still obtain stable voltage in emergency power supply mode, and avoid the load from interrupting operation due to insufficient voltage. 4. Stable output voltage, adaptable to load requirements: The feedback regulation module precisely regulates the output voltage of the buck converter module through the voltage division effect of two high-precision resistors, so that the output voltage is stable within the reasonable range required by the load and battery charging, avoiding damage to the load / battery due to excessive voltage or abnormal load due to excessive voltage, thus improving the circuit's adaptability to the load. 5. No additional control required, achieving automatic operation: The enable terminal (EN / SYNC) of the buck converter module is connected to the main power supply through a pull-up resistor, so the chip can be kept in working state without additional control signals. When the main power supply is normal, it automatically realizes "load power supply + battery charging" and automatically switches to "battery backup power supply" when the main power supply is disconnected. No manual intervention is required, improving the ease of use and reliability of the circuit. 6. Adapt to complex operating conditions and improve overall reliability: The selection of core components (such as MP2315 series step-down chips, low-resistance diodes, and high-precision resistors) is adapted to the complex working environment (such as voltage fluctuations and environmental changes) of three-phase energy meters and communication modules. At the same time, noise is filtered out and voltage is stabilized through decoupling capacitors, reducing the probability of circuit failure and ensuring long-term stable operation.

[0067] Implementation method of rechargeable battery protection circuit for power supply system of electricity meter The rechargeable battery protection circuit of the power supply system for the electricity meter of the present invention includes a step-down conversion module, a charging control module, and a rechargeable battery. The input terminal of the step-down conversion module is used to connect to an external power source, the output terminal of the step-down conversion module is connected to the input terminal of the charging control module, the output terminal of the charging control module is connected to the rechargeable battery to charge the rechargeable battery, and the output terminal of the rechargeable battery is used to connect to an external load to supply power to the external load. The step-down conversion module integrates an anti-backflow unit to prevent the current from the rechargeable battery from flowing back to the external power source. The charging control module is provided with a current limiting unit and a first unidirectional conduction unit. The current limiting unit is used to limit the charging current flowing from the charging control module to the rechargeable battery, and the first unidirectional conduction unit is used to ensure that the charging current flows unidirectionally to the rechargeable battery.

[0068] Specifically, such as Figure 1 As shown, the anti-backflow unit is the first diode D1. The anode of the first diode is electrically connected to the output terminal of the power input module, and the cathode of the first diode is electrically connected to the VIN pin (input pin) of the buck converter module. The first diode is model RB160M-60TR, and the package type is SOD-123. The anti-backflow unit uses a first diode D1 with a specific connection method. Utilizing the unidirectional conduction characteristic of the diode, it can effectively block the backflow path of the rechargeable battery current to the power input module (such as the 12V power supply pin of the energy meter), avoiding the uninterrupted loss of battery power when the main power supply is disconnected, and extending the battery backup power supply time. The specific package type of the diode adapts to the miniaturization design requirements of the circuit, meets the compact requirements of electronic equipment for internal space, and at the same time ensures the installation stability and electrical connection reliability of the diode in the circuit.

[0069] Specifically, in this embodiment, the current limiting unit is a current limiting resistor R2, and the first unidirectional conduction unit is a second diode D2; one end of the current limiting resistor R2 is electrically connected to the output terminal of the buck converter module, the other end of the current limiting resistor R2 is electrically connected to the anode of the second diode D2, and the cathode of the second diode D2 is electrically connected to the positive terminal of the rechargeable battery; the current limiting resistor R2 is of type RC-1206-100Ω-1 / 4W±1%±50ppm, the second diode D2 is of type 1N4148W, and the package type is SOD-123; the charging current limited by the current limiting resistor R2 is 45mA. The current-limiting resistor controls the charging current flowing to the battery through its own resistance characteristics, preventing excessive current from causing battery overheating and shortening its lifespan, or insufficient current from causing low charging efficiency, thus achieving balanced battery charging and extending battery life. The unidirectional conduction characteristic of the second diode D2 ensures that the charging current flows only from the buck converter module to the battery, preventing the current from flowing back into the charging control module when the battery is discharging, avoiding damage to circuit components and waste of battery power. The compatible component models and packages ensure that the charging control module works stably under different operating conditions, improving the safety and reliability of the charging process.

[0070] Specifically, in this embodiment, the battery power supply module integrates a second unidirectional conduction unit, which is a third diode D3; the anode of the third diode D3 is electrically connected to the positive terminal of the rechargeable battery, and the cathode of the third diode D3 serves as the output terminal of the battery power supply module; the third diode D3 is model RB160M-60TR, packaged in SOD-123 form, with a forward rectified current of not less than 1A and a forward voltage drop of not more than 0.4V.

[0071] The unidirectional conduction characteristic of the second diode prevents the current from the buck converter module from flowing into the battery through the battery power supply module when the main power supply is normal, thus avoiding overcharging of the battery and protecting its performance. The smaller forward voltage drop reduces voltage decay when the battery is powered, ensuring that the downstream load can still obtain a stable voltage in the backup power supply mode, and ensuring the normal operation of the load. Sufficient forward rectified current capability adapts to the maximum discharge demand of the battery, preventing the diode from being damaged due to insufficient current carrying capacity, ensuring uninterrupted backup power supply, and improving the reliability and continuity of backup power supply.

[0072] Specifically, in this embodiment, the feedback adjustment module includes a feedback resistor R6 and a feedback resistor R10; one end of the feedback resistor R6 is electrically connected to the output terminal of the buck converter module, and the other end of the feedback resistor R6 is electrically connected to the FB pin of the buck converter module, and also electrically connected to one end of the feedback resistor R10; the other end of the feedback resistor R10 is grounded; the model of the feedback resistor R6 is RC-0603-6.8kΩ-1 / 10W±1%±100ppm, and the model of the feedback resistor R10 is RC-0603-1.2kΩ-1 / 10W±1%±100ppm; the calculation formula for the target voltage VCC is VCC=(R6 / R10+1)×0.8, and VCC<5.5V, and the specific value of the target voltage VCC is 5.33V. Two feedback resistors precisely regulate the output voltage of the buck converter module through voltage division, stabilizing the output voltage within the range required by the load and battery charging. This prevents damage to the load or battery due to excessively high voltage, or abnormal load operation and low charging efficiency due to excessively low voltage. The parameter compatibility of the resistors ensures accurate voltage division ratio, reducing output voltage fluctuations caused by resistor errors. This provides a stable voltage foundation for power supply to the downstream load and battery charging, improving the overall power supply accuracy and stability of the circuit.

[0073] Specifically, in this embodiment, the buck converter module also includes an enable control unit, which is a pull-up resistor R4. One end of the pull-up resistor R4 is electrically connected to the output terminal of the power input module, and the other end of the pull-up resistor R4 is electrically connected to the EN / SYNC pin of the buck converter module. The pull-up resistor R4 is of type RC-0603-100kΩ-1 / 10W±5%±100ppm, used to keep the buck converter module in a continuous power conversion working state. The pull-up resistor pulls the voltage of the EN / SYNC pin to the power input voltage level, so that the buck converter module can be continuously in a working state without additional control signals. This ensures that when the main power supply is normal, the power supply to the downstream load and battery charging are uninterrupted, ensuring the continuity of circuit function. The appropriate resistor type ensures stable pull-up current and avoids abnormal EN / SYNC pin signals due to improper resistor values, thereby preventing frequent start-stop of the buck converter module and improving the stability and reliability of circuit operation.

[0074] Specifically, in this embodiment, the buck converter module further includes a pilot circuit unit, which consists of a pilot resistor R1 and a pilot capacitor C3. One end of the pilot resistor is electrically connected to the BST pin of the buck converter module, and the other end of the pilot resistor R1 is electrically connected to the SW pin of the buck converter module. The pilot capacitor is connected in parallel across the two ends of the pilot resistor. The pilot resistor is RC-0603-20Ω-1 / 10W±5%±100ppm, and the pilot capacitor is RC-0603-100nF / 50V±10% / X7R. The pilot circuit, composed of the pilot resistor and capacitor, provides a stable floating power supply to the high-side switch driver of the buck converter module, ensuring normal on and off of the high-side switch and avoiding a decrease in buck conversion efficiency or chip damage due to unstable driver power supply. The energy storage function of the capacitor and the current limiting function of the resistor work together to reduce voltage fluctuations during driver operation, improve the stability of the buck conversion process, and ensure that the buck converter module continuously outputs a stable voltage to meet the load and charging requirements.

[0075] Specifically, in this embodiment, the rechargeable battery is a 4.8V / 300mAh nickel-metal hydride battery with a maximum discharge current of not less than 900mA; the external load includes the input terminal of the power conversion chip of the remote 5G module and the input terminal of the voltage regulator chip of the main control MCU; the 12V input voltage of the power input module is obtained from pins 1 and 2 of the three-phase energy meter and the low-voltage interface of the communication module. The characteristics of the nickel-metal hydride battery are adapted to the backup power supply requirements, providing a stable discharge voltage and sufficient backup power supply time, ensuring that the back-end load can still work normally after the main power supply is disconnected; the clear load type (power conversion chip of the remote 5G module, voltage regulator chip of the main control MCU) allows the circuit design to be specifically adapted to the actual application scenario, avoiding power supply problems caused by improper load matching, and ensuring the reliable operation of loads with high power consumption or high stability requirements; the specific power input source (three-phase energy meter, low-voltage interface of the communication module) allows the circuit to conveniently obtain the main power supply without an additional power supply interface, improving the compatibility and practicality of the circuit with existing equipment.

[0076] Specifically, in this embodiment, a decoupling capacitor C1 is connected in parallel at the input terminal of the buck converter module. The decoupling capacitor C1 is an ESR capacitor with a capacitance of 22μF. A decoupling capacitor Cvcc is also connected in parallel at the VCC pin of the buck converter module. The decoupling capacitor Cvcc is of type RC-0603-100nF / 50V±10% / X7R. The AAM pin of the buck converter module is also grounded through a resistor R9. The resistor R9 is of type RC-0603-100kΩ-1 / 10W±5%±100ppm, which is used to set the buck converter module to asynchronous mode when the load is low. The ESR decoupling capacitor alleviates the problem of discontinuous input current in the buck converter at the power input terminal, stabilizes the input voltage, reduces the impact of voltage fluctuations on buck conversion, and improves conversion efficiency. The decoupling capacitor filters out high-frequency noise from the VCC pin, providing a clean bias voltage for the buck converter module, ensuring stable operation of the internal circuitry of the chip, and reducing chip performance abnormalities caused by noise interference. The grounding resistor of the AAM pin sets the module to asynchronous mode when the load is small, adapting to light load conditions, reducing energy loss under light load, and improving the adaptability and energy utilization efficiency of the circuit under different load conditions.

[0077] Therefore, the rechargeable battery protection circuit of the power supply system of the present invention can automatically realize load power supply and battery charging during main power supply and battery backup power supply during power failure, avoid ineffective battery loss, ensure stable operation of the load, and improve circuit reliability and rechargeable battery life.

Claims

1. A protection circuit for a rechargeable battery of a power supply system of an electric energy meter, characterized in that, The protection circuit includes a step-down converter module, a charging control module, and a rechargeable battery. The input terminal of the step-down converter module is used to connect to an external power source. The output terminal of the step-down converter module is connected to the input terminal of the charging control module. The output terminal of the charging control module is connected to the rechargeable battery to charge the rechargeable battery. The output terminal of the rechargeable battery is used to connect to an external load to supply power to the external load. The step-down converter module integrates an anti-backflow unit to prevent the current from the rechargeable battery from flowing back to the external power source; the charging control module is equipped with a current limiting unit and a first unidirectional conduction unit. The current limiting unit is used to limit the charging current flowing from the charging control module to the rechargeable battery, and the first unidirectional conduction unit is used to ensure that the charging current flows unidirectionally to the rechargeable battery.

2. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 1, characterized in that, The buck converter module uses a high-frequency synchronous rectification buck switching mode converter as the core chip. The output pin of the converter is also connected to a feedback regulation module, which is used to regulate the output voltage of the converter so that the converter outputs a stable target voltage.

3. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 2, characterized in that, The backflow prevention unit uses a first diode, the anode of which is connected to an external power supply, and the cathode of which is connected to the input pin of the converter.

4. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 1, characterized in that, The current limiting unit uses a current limiting resistor, the first unidirectional conduction unit uses a second diode, one end of the current limiting resistor is connected to the output terminal of the buck converter module, the other end of the current limiting resistor is connected to the anode of the second diode, and the cathode of the second diode is connected to the positive terminal of the rechargeable battery.

5. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 1, characterized in that, The output terminal of the rechargeable battery is connected to an external load through a second unidirectional conduction unit. The second unidirectional conduction unit uses a third diode. The anode of the third diode is connected to the positive terminal of the rechargeable battery, and the cathode of the third diode is used to connect to the external load, serving as the output terminal of the power supply system.

6. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 2, characterized in that, The feedback adjustment module includes two feedback resistors connected in series. The output pin of the converter is grounded through the two feedback resistors connected in series, and the connection point of the two feedback resistors is connected to the feedback pin of the converter.

7. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 2, characterized in that, The enable pin of the converter is connected to an external power supply via a pull-up resistor.

8. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 2, characterized in that, The buck converter module also includes a boot circuit unit, which includes a boot resistor and a boot capacitor. One end of the boot resistor is connected to the bootstrap pin of the converter, and the other end of the boot resistor is connected to the output pin of the converter through the boot capacitor.

9. The rechargeable battery protection circuit of the power supply system for the electricity meter according to claim 2, characterized in that, The converter's input pins are also connected in parallel with decoupling capacitors, the converter's VCC pin is connected in parallel with a decoupling capacitor, and the converter's AAM pin is grounded through a resistor.

10. A power supply system for an electricity meter, comprising a power input module and a rechargeable battery protection circuit, characterized in that, The power input module is used to provide external power to the rechargeable battery protection circuit, which adopts the rechargeable battery protection circuit of the power supply system of the electricity meter according to any one of claims 1-9.

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