A circuit for realizing fast and stable charging of RTC capacitor by adopting constant current source

Abstract

The utility model relates to electronic circuit technical field discloses a kind of circuit for realizing the quick stable charging of RTC capacitor using constant current source, including LDO constant current source module, main power module, backup power charging module and RTC module, the power supply input end of LDO constant current source module is electrically connected with the output end of main power module, the output end of LDO constant current source module is electrically connected with backup power charging module, the output end of backup power charging module is electrically connected with the power input end of RTC module, the output end of main power module is electrically connected with RTC module.The utility model in, by using LDO constant current source to RTC can realize quick stable charging, ordinary charging circuit needs several minutes, this improved circuit only needs 10S, and the circuit is realized by the cooperation of multiple modules RTC module's sustained accurate timing and backup power's quick stable charging.

Description

Technical Field

[0001] This utility model relates to the field of electronic circuit technology, and in particular to a circuit that uses a constant current source to achieve fast and stable charging of an RTC capacitor. Background Technology

[0002] Real-time clock (RTC) circuits play a crucial role in various electronic devices, such as smart home systems, industrial automation equipment, medical instruments, and communication base stations. They provide precise time information to ensure that the device's functions are executed in an orderly manner according to predetermined times. Therefore, it is necessary to develop a circuit that uses a constant current source to quickly and stably charge the RTC capacitor.

[0003] A circuit that uses a constant current source to achieve fast and stable charging of RTC capacitors. In previous technologies, the traditional current-limiting resistor charging method was slow, often taking several minutes or even longer to fully charge, which was inefficient. In addition, in the early stages of charging, surge current may impact the main power supply system, affecting the overall stability. Utility Model Content

[0004] To overcome the above shortcomings, this utility model provides a circuit that uses a constant current source to achieve fast and stable charging of RTC capacitors. It aims to improve the problem that the traditional current-limiting resistor charging method in the prior art is slow, often takes several minutes or even longer to fully charge, is inefficient, and may affect the overall stability due to surge current impacting the main power supply system in the early stage of charging.

[0005] To achieve the above objectives, this utility model provides the following technical solution: a circuit for rapidly and stably charging an RTC capacitor using a constant current source, comprising an LDO constant current source module, a main power supply module, a backup power charging module, and an RTC module. The power input terminal of the LDO constant current source module is electrically connected to the output terminal of the main power supply module, the output terminal of the LDO constant current source module is electrically connected to the backup power charging module, the output terminal of the backup power charging module is electrically connected to the power input terminal of the RTC module, and the output terminal of the main power supply module is electrically connected to the RTC module. The main power supply module includes main power supplies VDD_3V3_MAIN and VDD_5V0_MAIN, where VDD_3V3_MAIN supplies power to the RTC module, and VDD_5V0_MAIN supplies power to the LDO constant current source module.

[0006] Preferably, the RTC module includes an RTC chip U7. The X1 pin of the RTC chip U7 is connected to one end of a crystal oscillator Y2, and the X2 pin is connected to the other end of the crystal oscillator Y2. Pin 1 of the crystal oscillator Y2 is connected to one end of a load capacitor C73, and the other end of the load capacitor C73 is grounded. Pin 2 of the crystal oscillator Y2 is connected to one end of a load capacitor C74, and the other end of the load capacitor C74 is grounded.

[0007] Preferably, the INTA pin of the RTC chip U7 is connected to one end of a pull-up resistor R367, the other end of the pull-up resistor R367 is connected to the main power supply VDD_3V3_MAIN, and the GND pin of the RTC chip U7 is directly grounded.

[0008] Preferably, the VCC pin of the RTC chip U7 is connected to the cathode of a Schottky diode D51, and the anode of the Schottky diode D51 is connected to the main power supply VDD_3V3_MAIN. A capacitor C239 and a capacitor C59 are connected in parallel between the main power supply VDD_3V3_MAIN and ground. The parallel connection of capacitors C239 and C59 is used for filtering, stabilizing the power supply voltage, and reducing the impact of power supply noise on the chip.

[0009] Preferably, the INTB pin of the RTC chip U7 is connected to one end of a pull-up resistor R54, and the other end of the pull-up resistor R54 is connected to the main power supply VDD_3V3_MAIN. The SCL pin of the RTC chip U7 is the serial clock line of the I²C bus, and the SDA pin of the RTC chip U7 is the serial data line of the I²C bus. The SCL pin of the RTC chip U7 is connected to one end of a resistor R46, and the other end of the resistor R46 is connected to the clock line of the external I²C bus. The SDA pin of the RTC chip U7 is connected to one end of a resistor R51, and the other end of the resistor R51 is connected to the data line of the external I²C bus. The SCL pin of the RTC chip U7 is connected to one end of a pull-up resistor R43, and the SDA pin of the RTC chip U7 is connected to one end of a pull-up resistor R52. The other ends of both pull-up resistors R43 and R52 are connected to the main power supply VDD_3V3_MAIN to ensure that the I²C bus remains at a high level in the idle state and to stabilize the communication signal.

[0010] Preferably, the LDO constant current source module includes an LDO chip U34, a filter capacitor C240, and a pull-up resistor R368. The VIN pin of the LDO chip U34 is electrically connected to the VDD_5V0_MAIN output terminal of the main power supply module. The two ends of the filter capacitor C240 ​​are connected in parallel between VDD_5V0_MAIN and ground. The EN pin of the LDO chip U34 is connected to one end of the pull-up resistor R368, and the other end of the pull-up resistor R368 is connected to the VDD_5V0_MAIN output terminal of the main power supply module.

[0011] Preferably, the CP pin of the LDO chip U34 is connected to one end of a filter capacitor C242, the other end of the filter capacitor C242 is connected to the CN pin of the chip, the output OUT pin of the LDO chip U34 is connected to one end of a filter capacitor C241, the other end of the filter capacitor C241 is grounded, the filter capacitor C241 is connected in parallel between the output OUT pin of the LDO chip U34 and ground, and the GND pin of the LDO chip U34 is directly grounded.

[0012] Preferably, the backup power charging module includes a Schottky diode D50 and a VCC_CBAT backup power supply. The VCC_CBAT backup power supply is connected to the anode of a Schottky diode D48, and the cathode of the Schottky diode D48 is connected to the VCC pin of the RTC chip U7. The anode of the Schottky diode D50 is connected to the OUT pin of the LDO chip U34, and the cathode of the diode D50 is connected to the VCC_CBAT backup power supply. The VCC_CBAT backup power supply is connected to one end of an electrolytic capacitor C61, and the other end of the electrolytic capacitor C61 is grounded. The VCC_CBAT backup power supply is connected to a BAT1 battery.

[0013] This utility model has the following beneficial effects: 1. In this utility model, by combining the dual power supply of the main power module with the LDO constant current source module, stable power supply to the RTC module and fast and reliable charging of the backup power supply are achieved. Through the dual-path design of direct main power supply plus constant current fast charging backup power supply, the continuity of real-time timing of the RTC module is guaranteed, and the charging efficiency and stability of the backup power supply are improved. By using the LDO constant current source to charge the RTC, fast and stable charging can be achieved. Ordinary charging circuits require several minutes, while this improved circuit only requires 10 seconds. This circuit achieves continuous and accurate timing of the RTC module and fast and stable charging of the backup power supply through the collaborative work of multiple modules.

[0014] 2. In this utility model, the LDO module ensures stable and controllable charging current, while the backup power module, through the combination of capacitor and battery, takes into account both rapid response during power failure and long-term power supply capability, providing dual protection for the continuous operation of the RTC module, ensuring uninterrupted power supply to the RTC module and no loss of time information when the main power supply fails. Attached Figure Description

[0015] Figure 1 This is a circuit connection diagram of a circuit that uses a constant current source to achieve fast and stable charging of an RTC capacitor, as proposed in this utility model. Figure 2 This utility model presents a schematic block diagram of a circuit that uses a constant current source to achieve rapid and stable charging of an RTC capacitor. Detailed Implementation

[0016] The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0017] Reference Figure 1 and Figure 2 This utility model provides an embodiment of a circuit for rapidly and stably charging an RTC capacitor using a constant current source. The circuit includes an LDO constant current source module, a main power supply module, a backup power charging module, and an RTC module. The power input terminal of the LDO constant current source module is electrically connected to the output terminal of the main power supply module. The output terminal of the LDO constant current source module is electrically connected to the backup power charging module. The output terminal of the backup power charging module is electrically connected to the power input terminal of the RTC module. The output terminal of the main power supply module is electrically connected to the RTC module. The main power supply module includes main power supplies VDD_3V3_MAIN and VDD_5V0_MAIN. The main power supply VDD_3V3_MAIN powers the RTC module, and the main power supply VDD_5V0_MAIN powers the LDO constant current source module. Specifically, the LDO constant current source module receives the main power supply VDD_5V0_MAIN input and outputs a stable DC current through its internal voltage regulation and constant current circuitry. This provides a controllable charging current specifically for the backup power supply charging module, ensuring current stability during charging and preventing damage to the backup energy storage components due to excessive current. It also enables fast and efficient charging, ensuring the backup power supply can quickly store sufficient energy when the main power supply is functioning normally. The main power supply module contains two power circuits, VDD_3V3_MAIN and VDD_5V0_MAIN, which are the primary energy sources. VDD_3V3_MAIN directly powers the RTC module, meeting the RTC chip's operating voltage requirements and ensuring its normal timing, communication, and interrupt functions. VDD_5V0_MAIN serves as the input power for the LDO constant current source module, providing the energy foundation for charging the backup power supply. This separates the charging paths of the main power supply and backup power supply, preventing mutual interference. When the main power supply is functioning normally, the backup power supply charging module receives the current output from the LDO constant current source module for energy storage. When the main power supply is interrupted, the RTC module can maintain normal operation, ensuring that time information is not lost. Through the RTC module, accurate counting of time information such as seconds, minutes, hours, and days can be achieved, and communication with external devices is supported through interfaces such as I2C, supporting time reading and setting. The main power supply VDD_5V0_MAIN supplies power to the LDO constant current source module, which, after voltage and current regulation, can provide a stable charging current for the backup power charging module, ensuring that the backup capacitor is quickly charged and avoiding overcharging. The main power supply VDD_3V3_MAIN directly supplies power to the RTC module, ensuring its normal operation. At the same time, through the connection between the backup power charging module and the power input terminal of the RTC module, the power supply can automatically switch to the RTC module when the main power supply is interrupted. Through this dual main power supply division of labor design, the direct requirements of the RTC module for operating voltage are met, and the LDO constant current source provides stable and controllable charging conditions for the backup power supply. This ensures that when the main power supply is normal, it can maintain the real-time timing of the RTC and efficiently store energy for the backup power supply, achieving seamless power switching when the main power supply is interrupted.

[0018] Reference Figure 1 and Figure 2The RTC module includes an RTC chip U7. Pin X1 of the RTC chip U7 is connected to one end of crystal oscillator Y2, and pin X2 is connected to the other end of crystal oscillator Y2. Pin 1 of crystal oscillator Y2 is connected to one end of load capacitor C73, and the other end of load capacitor C73 is grounded. Pin 2 of crystal oscillator Y2 is connected to one end of load capacitor C74, and the other end of load capacitor C74 is grounded. Pin INTA of the RTC chip U7 is connected to one end of pull-up resistor R367, and the other end of pull-up resistor R367 is connected to… Connect the main power supply VDD_3V3_MAIN, and the GND pin of the RTC chip U7 is directly grounded; the VCC pin of the RTC chip U7 is connected to the cathode of the Schottky diode D51, and the anode of the Schottky diode D51 is connected to the main power supply VDD_3V3_MAIN. Capacitors C239 and C59 are connected in parallel between the main power supply VDD_3V3_MAIN and ground. The parallel connection of capacitors C239 and C59 is used for filtering, stabilizing the power supply voltage, and reducing the impact of power supply noise on the chip. Specifically, the clock oscillation circuit is formed by connecting the X1 and X2 pins of the RTC chip U7 to the crystal oscillator Y2 and the load capacitors C73 and C74. Load capacitors C73 and C74 stabilize the frequency of the crystal oscillator Y2. Simultaneously, both load capacitors C73 and C74 are grounded to release high-frequency noise, ensuring a clean clock signal and a precise clock reference for the RTC chip U7, guaranteeing timing accuracy and avoiding timing errors caused by frequency drift. Pull-up resistor R367 stabilizes the default level of the INTA pin of the RTC chip U7 at a high level consistent with VDD_3V3_MAIN, preventing the pin from floating. Due to electromagnetic interference causing level fluctuations, when the RTC chip U7 triggers an interrupt, the INTA pin will actively pull low, forming a clear high-to-low transition signal. This facilitates reliable identification of the interrupt event by external control equipment, ensuring the accuracy of timing, alarm, and other functions. Furthermore, this resistor ensures level stability and limits the current flowing into the U7 chip, preventing pin damage from overcurrent. Directly grounding the GND pin of the RTC chip U7 provides a zero-potential reference for the chip, giving the voltage signals of each pin a clear reference point and ensuring the normal operation of the internal circuitry. Simultaneously, the ground plane serves as a signal return path, absorbing circuit noise and reducing... To reduce interference between power supply and signal, overall stability is improved. The main power supply VDD_3V3_MAIN is connected to the VCC pin of the RTC chip U7 via Schottky diode D51, providing power for the chip during normal operation. Diode D51 also prevents reverse current flow, ensuring that current flows only from the main power supply to the chip. The backup power supply VCC_CBAT is also connected to the VCC pin of the RTC chip U7 via Schottky diode D48. When the main power supply VDD_3V3_MAIN is de-energized, Schottky diode D48 conducts, and VCC_CBAT supplies power to the chip, thus ensuring the RTC chip U7's... Continuous operation maintains the time counting. Simultaneously, the large-value capacitor C239 filters out low-frequency ripple in the power supply, stabilizing the DC level of the main power supply. The low capacitive reactance of the small-value capacitor C59 absorbs high-frequency noise, preventing high-frequency signals from coupling to the RTC chip U7. The synergy of capacitors C239 and C59 ensures the purity of the main power supply, filtering out high-frequency noise and ripple in the main power supply VDD_3V3_MAIN, making the power output to the RTC chip U7 purer and more stable. This guarantees stable circuit operation, reduces power supply noise interference to the clock oscillation circuit and internal logic, and further ensures timing accuracy.

[0019] Reference Figure 1The INTB pin of RTC chip U7 is connected to one end of pull-up resistor R54, and the other end of pull-up resistor R54 is connected to the main power supply VDD_3V3_MAIN. The SCL pin of RTC chip U7 is the serial clock line of the I²C bus, and the SDA pin of RTC chip U7 is the serial data line of the I²C bus. The SCL pin of RTC chip U7 is connected to one end of resistor R46, and the other end of resistor R46 is connected to the clock line of the external I²C bus. The SDA pin of RTC chip U7 is connected to one end of resistor R51, and the other end of resistor R51 is connected to the data line of the external I²C bus. The SCL pin of RTC chip U7 is connected to one end of pull-up resistor R43, and the SDA pin of RTC chip U7 is connected to one end of pull-up resistor R52. The other ends of pull-up resistors R43 and R52 are both connected to the main power supply VDD_3V3_MAIN to ensure that the I²C bus remains at a high level in the idle state and to stabilize the communication signal. Specifically, pull-up resistor R54 keeps the INTB pin high in the absence of interrupt events, providing a clear no-interrupt quasi-state for the master control device. When the RTC chip U7 triggers an INTB-related interrupt, the chip internally pulls the INTB pin low, creating a high-to-low level transition. This facilitates rapid interrupt signal recognition by the master control device, preventing random level fluctuations caused by electromagnetic interference and environmental noise when the INTB pin is floating. This ensures that only genuine interrupt events trigger level changes, improving the reliability of the interrupt signal. It also keeps the high level of the INTB pin consistent with the main power supply VDD_3V3_MAIN, ensuring compatibility with the I / O port levels of external devices and guaranteeing signal transmission compatibility and accuracy. The SCL pin (serial clock line) of the RTC chip U7 is connected to the external I²C bus clock line via resistor R46, and the SDA pin (serial data line) is connected to the external I²C bus data line via resistor R51. Resistors R46 and R51 are current-limiting resistors, protecting the SCL and SDA pins of the RTC chip respectively. When an abnormal voltage occurs on the external I²C bus, current is limited. Resistors limit the current flowing into the chip pins, preventing overcurrent damage to the internal drive circuit. Simultaneously, they suppress high-frequency oscillations in the bus signal, reducing signal reflection. Especially with long bus lengths, they improve signal integrity and ensure the stability of I²C communication. The SCL and SDA pins of the RTC chip U7 are connected to the main power supply VDD_3V3_MAIN via pull-up resistors R43 and R52, respectively. These resistors provide a high-level drive capability for the I²C bus, ensuring the bus maintains a stable high level in idle states and preventing level fluctuations or misjudgments caused by floating signals. Furthermore, pull-up resistors R43 and R52 enhance the bus drive capability, improve signal integrity when multiple devices are connected, reduce noise interference, and ensure the stability and accuracy of the serial clock line SCL and serial data line SDA signal transmission. This ensures reliable I²C communication between the RTC chip U7 and external devices. A test point T20 is provided on the serial clock line of the RTC chip U7's SCL pin, and a test point T21 is provided on the serial data line of the RTC chip U7's SDA pin.

[0020] Reference Figure 1 and Figure 2The LDO constant current source module includes an LDO chip U34, a filter capacitor C240, and a pull-up resistor R368. The VIN pin of the LDO chip U34 is electrically connected to the VDD_5V0_MAIN output of the main power supply module. The two ends of the filter capacitor C240 ​​are connected in parallel between VDD_5V0_MAIN and ground. The EN pin of the LDO chip U34 is connected to one end of the pull-up resistor R368, and the other end of the pull-up resistor R368 is connected to the VDD_5V0_MAIN output of the main power supply module. The CP pin of the LDO chip U34 is connected to one end of the filter capacitor C242, and the other end of the filter capacitor C242 is connected to the CN pin of the chip. The OUT pin of the LDO chip U34 is connected to one end of the filter capacitor C241. The other end is grounded. The filter capacitor C241 is connected in parallel between the output OUT pin of the LDO chip U34 and ground. The GND pin of the LDO chip U34 is directly grounded. The backup power charging module includes a Schottky diode D50 and a VCC_CBAT backup power supply. The VCC_CBAT backup power supply is connected to the anode of the Schottky diode D48. The cathode of the Schottky diode D48 is connected to the VCC pin of the RTC chip U7. The anode of the Schottky diode D50 is connected to the OUT pin of the LDO chip U34. The cathode of the diode D50 is connected to the VCC_CBAT backup power supply. The VCC_CBAT backup power supply is connected to one end of an electrolytic capacitor C61. The other end of the electrolytic capacitor C61 is grounded. The VCC_CBAT backup power supply is connected to a BAT1 battery. Specifically, VDD_5V0_MAIN provides the input voltage for the LDO chip U34, meeting its operating voltage requirements. Filter capacitor C240 ​​filters out high-frequency noise from the main power supply, preventing input voltage fluctuations from affecting the LDO's internal voltage regulation circuit, ensuring a clean input voltage and laying the foundation for stable output. The EN pin of the LDO chip U34 is the enable pin; connecting pull-up resistor R368 pulls its default level high, ensuring the LDO chip U34 automatically starts working after power-on without external control signals. Simultaneously, pull-up resistor R358 prevents level fluctuations when the EN pin is floating, which could cause the LDO to shut down erroneously, ensuring continuous and stable module operation. The CP pin of the LDO chip U34... The CN pin is typically the compensation terminal for the internal adjustment circuit of the LDO. Connecting a filter capacitor C242 stabilizes the operating point of the internal error amplifier, preventing circuit self-oscillation and ensuring the stability of the LDO's output voltage and current, especially enabling rapid response to load changes and reducing output ripple. A filter capacitor C241 connected to the constant current output (OUT) pin of the LDO chip U34 filters out high-frequency ripple in the output current, making it smoother. Simultaneously, this filter capacitor C241 provides instantaneous current replenishment during load transients, enhancing the LDO's dynamic response and ensuring stable charging current to the backup power supply. Grounding the GND pin of the LDO chip U34 directly provides a zero-potential reference, ensuring the LDO's stability. The internal circuit operates normally and also serves as a current return path, reducing circuit noise interference. The charging current output from the LDO flows to VCC_CBAT through D50 to charge the backup power supply. The Schottky diode D50 is connected to the OUT pin of the LDO chip U34. Schottky diode D50 is a reverse-current protection diode; by utilizing its unidirectional conductivity, when the main power supply is interrupted and the LDO stops outputting, D50 reverse-cuts off, preventing energy in VCC_CBAT from flowing back through the LDO. This ensures that current can only flow from the LDO constant current source to the backup power supply and cannot flow in the reverse direction, thus protecting the LDO chip and improving the overall circuit reliability. The connected electrolytic capacitor C61 serves as the main storage... The energy storage element stores the energy provided by the LDO when the main power supply is normal. When the main power supply fails, it quickly releases the energy to power the RTC module, achieving seamless power supply switching. Simultaneously, the electrolytic capacitor C61 filters out noise in VCC_CBAT, ensuring stable output voltage. The BAT1 battery serves as a long-term energy storage unit, replacing the energy storage capacitor to continuously power VCC_CBAT during prolonged main power outages, ensuring the RTC module maintains its timing function for weeks or even months, preventing time information loss. Furthermore, a backup power supply is designed for VCC_CBAT, with one end connected to resistor R369, and the other end of resistor R369 connected to the cathode of Schottky diode D49.The anode of Schottky diode D49 is connected to the main power supply VDD_5V0_MAIN. Due to the unidirectional conductivity of Schottky diode D49, when the voltage of the VCC_CBAT backup power supply abnormally rises and exceeds the voltage of the main power supply VDD_5V0_MAIN, diode D49 will cut off, preventing current from the backup power supply from flowing back to the main power supply. This avoids the main power supply being impacted by abnormal voltage, protecting the main power supply and its connected circuit modules from damage. Through this reserved connection method, under certain circumstances, the main power supply VDD_5V0_MAIN can pre-charge the VCC_CBAT backup power supply through diode D49 and resistor R369. Resistor R369 acts as a current limiter, preventing excessive charging current from damaging the energy storage components in the backup power supply.

[0021] Working Principle: During operation, the main power module provides two power supplies: VDD_3V3_MAIN and VDD_5V0_MAIN. VDD_3V3_MAIN directly powers the RTC module, ensuring the normal timing of the RTC chip U7. The RTC chip U7 in the RTC module is connected to an external crystal oscillator Y2 and load capacitors C73 and C74 via pins X1 and X2 to form a clock oscillation circuit. This generates a precise clock reference for time counting. It also connects to an external I²C bus via pins SCL and SDA, and is supported by pull-up resistors R367 and R54. It can maintain the I²C bus idle high level to ensure stable communication, while the INTA and INTB pins achieve reliable transmission of interrupt signals through pull-up resistors. The LDO constant current source module is powered by the main power supply VDD_5V0_MAIN. The LDO chip U34 purifies the input power supply through filter capacitor C240, maintains the enabled state through pull-up resistor R368 on the EN pin, and uses compensation capacitor C242 on the CP and CN pins to stabilize the output. Finally, a stable constant current is output from the output OUT pin, and then smoothed by output filter capacitor C241 before passing through a low-loss anti-reverse Schottky diode. Diode D50 supplies power to the backup power charging module. Electrolytic capacitor C61 is the energy storage capacitor connected to the VCC_CBAT backup power supply. It stores energy from the LDO constant current source when the main power supply is normal, and quickly releases this energy to power the RTC module after a power outage, achieving seamless power switching. Capacitor C61 can utilize its low ESR characteristics to quickly absorb large currents for fast charging within 10 seconds. The BAT1 battery provides long-term battery life. Schottky diode D50 can charge the electrolytic capacitor C61 and the BAT1 battery in the backup power charging module. Schottky diode D50 is designed to prevent... The reverse-current diode has the characteristic of low forward voltage drop, which can prevent the charging current from flowing back. When the main power supply is interrupted, the time information is not lost. When the main power supply is interrupted, the backup power supply VCC_CBAT automatically switches to power the RTC chip U7 through the Schottky diode D48. The unidirectional conduction characteristic of the diode can ensure that there is no conflict between the main power supply and the backup power supply. In conjunction with the filter capacitors C239 and C59 on the main power supply side, the power supply is further stabilized. Ultimately, the RTC module can accurately time when the main power supply is normal, quickly store energy with the backup power supply, and seamlessly switch power supply when the main power supply is interrupted to keep the time from being lost. The LDO chip U34 has a fast response capability, enabling it to quickly adjust its output and maintain a stable charging current when the load changes. When the energy storage capacitor C61 in the backup power supply begins charging, its voltage gradually increases, and the load characteristics change. The LDO constant current source can quickly sense this and make adjustments to ensure that the charging current does not fluctuate significantly with load changes, continuously and efficiently charging the backup power supply. In the LDO constant current source module, capacitor C240 ​​filters out high-frequency noise from the main power input, ensuring a clean LDO input voltage. Capacitor C242 stabilizes the operating point of the internal adjustment circuit of the LDO, preventing self-oscillation. Capacitor C241 filters out high-frequency ripple in the LDO output current, making the output current smoother and more stable. These filters... The capacitor ensures that the LDO constant current source module operates in a stable working environment, avoiding the impact of power supply noise, oscillation, and other issues on the stability of the charging current and charging efficiency, thus facilitating fast charging. The backup power supply consists of energy storage capacitor C61 and BAT1 battery. In the initial stage of fast charging, capacitor C61 mainly absorbs the large current output from the LDO constant current source for energy storage. The capacitor charges quickly and can store a large amount of electrical energy in a short time. When the capacitor is close to being fully charged, the subsequent small current can trickle charge the BAT1 battery to replenish its power. Through the synergistic energy storage of energy storage capacitor C61 and BAT1 battery, the fast energy storage characteristics of the capacitor are utilized to achieve fast charging, while ensuring that the backup power supply has enough power to maintain power supply for a long time.

[0022] Finally, it should be noted that the above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A circuit for rapidly and stably charging an RTC capacitor using a constant current source, comprising an LDO constant current source module, a main power supply module, a backup power supply charging module, and an RTC module, characterized in that: The power input terminal of the LDO constant current source module is electrically connected to the output terminal of the main power supply module. The output terminal of the LDO constant current source module is electrically connected to the backup power charging module. The output terminal of the backup power charging module is electrically connected to the power input terminal of the RTC module. The output terminal of the main power supply module is electrically connected to the RTC module. The main power supply module includes main power supplies VDD_3V3_MAIN and VDD_5V0_MAIN. The main power supply VDD_3V3_MAIN supplies power to the RTC module, and the main power supply VDD_5V0_MAIN provides power to the LDO constant current source module.

2. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 1, characterized in that: The RTC module includes an RTC chip U7. The X1 pin of the RTC chip U7 is connected to one end of the crystal oscillator Y2, and the X2 pin is connected to the other end of the crystal oscillator Y2. Pin 1 of the crystal oscillator Y2 is connected to one end of the load capacitor C73, and the other end of the load capacitor C73 is grounded. Pin 2 of the crystal oscillator Y2 is connected to one end of the load capacitor C74, and the other end of the load capacitor C74 is grounded.

3. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 2, characterized in that: The INTA pin of the RTC chip U7 is connected to one end of a pull-up resistor R367, and the other end of the pull-up resistor R367 is connected to the main power supply VDD_3V3_MAIN. The GND pin of the RTC chip U7 is directly grounded.

4. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 2, characterized in that: The VCC pin of the RTC chip U7 is connected to the cathode of a Schottky diode D51. The anode of the Schottky diode D51 is connected to the main power supply VDD_3V3_MAIN. Capacitors C239 and C59 are connected in parallel between the main power supply VDD_3V3_MAIN and ground. The parallel connection of capacitors C239 and C59 is used for filtering, stabilizing the power supply voltage, and reducing the impact of power supply noise on the chip.

5. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 2, characterized in that: The INTB pin of the RTC chip U7 is connected to one end of a pull-up resistor R54, and the other end of the pull-up resistor R54 is connected to the main power supply VDD_3V3_MAIN. The SCL pin of the RTC chip U7 is the serial clock line of the I²C bus, and the SDA pin of the RTC chip U7 is the serial data line of the I²C bus. The SCL pin of the RTC chip U7 is connected to one end of a resistor R46, and the other end of the resistor R46 is connected to the clock line of the external I²C bus. The SDA pin of the RTC chip U7 is connected to one end of a resistor R51, and the other end of the resistor R51 is connected to the data line of the external I²C bus. The SCL pin of the RTC chip U7 is connected to one end of a pull-up resistor R43, and the SDA pin of the RTC chip U7 is connected to one end of a pull-up resistor R52. The other ends of both pull-up resistors R43 and R52 are connected to the main power supply VDD_3V3_MAIN to ensure that the I²C bus remains at a high level in the idle state and to stabilize the communication signal.

6. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 1, characterized in that: The LDO constant current source module includes an LDO chip U34, a filter capacitor C240, and a pull-up resistor R368. The VIN pin of the LDO chip U34 is electrically connected to the VDD_5V0_MAIN output terminal of the main power supply module. The two ends of the filter capacitor C240 ​​are connected in parallel between VDD_5V0_MAIN and ground. The EN pin of the LDO chip U34 is connected to one end of the pull-up resistor R368, and the other end of the pull-up resistor R368 is connected to the VDD_5V0_MAIN output terminal of the main power supply module.

7. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 6, characterized in that: The CP pin of the LDO chip U34 is connected to one end of a filter capacitor C242, and the other end of the filter capacitor C242 is connected to the CN pin of the chip. The output OUT pin of the LDO chip U34 is connected to one end of a filter capacitor C241, and the other end of the filter capacitor C241 is grounded. The filter capacitor C241 is connected in parallel between the output OUT pin of the LDO chip U34 and ground. The GND pin of the LDO chip U34 is directly grounded.

8. The circuit for rapidly and stably charging an RTC capacitor using a constant current source according to claim 1, characterized in that: The backup power charging module includes a Schottky diode D50 and a VCC_CBAT backup power supply. The VCC_CBAT backup power supply is connected to the anode of a Schottky diode D48. The cathode of the Schottky diode D48 is connected to the VCC pin of the RTC chip U7. The anode of the Schottky diode D50 is connected to the OUT pin of the LDO chip U34. The cathode of the diode D50 is connected to the VCC_CBAT backup power supply. One end of the VCC_CBAT backup power supply is connected to an electrolytic capacitor C61, and the other end of the electrolytic capacitor C61 is grounded. The VCC_CBAT backup power supply is connected to a BAT1 battery.

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