A solar charger step-down charging module

Abstract

This utility model discloses a step-down charging module for a solar charger, comprising: a photovoltaic input terminal; a multi-stage input filter network disposed at the photovoltaic input terminal; a P-channel MOSFET switch connected to the photovoltaic input terminal; a first Schottky diode (D2); a controller (U4); a second Schottky diode (D1) connected between the output terminal of the first Schottky diode (D2) and ground; an energy storage inductor (LX3); a current sampling resistor (RCS) connected in series between the energy storage inductor (LX3) and the battery terminal; output filter capacitors (C32, C33) connected between the battery terminal and ground; and an RC absorption network connected between the output terminal of the first Schottky diode (D2) and ground. This utility model has the following advantages: this step-down charging module for a solar charger features high efficiency, high reliability, low noise, and high-precision charging control.

Description

Technical Field

[0001] This utility model relates to a step-down charging module for a solar charger. Background Technology

[0002] With the escalating global energy crisis and increased environmental awareness, solar energy, as a clean and renewable energy source, is being widely applied across various sectors. Particularly in scenarios such as small off-grid devices, road signs, data acquisition terminals, environmental monitoring stations, and agricultural irrigation systems, solar charging systems have become a primary power supply solution. However, existing solar chargers have revealed numerous technical shortcomings in practical applications, severely hindering the promotion and efficiency improvement of solar energy applications.

[0003] Firstly, regarding backfeed protection, existing solar chargers generally employ a single-diode backfeed protection scheme. This traditional design has significant drawbacks: on the one hand, the series-connected diode generates an inherent voltage drop of 0.5-0.7V, resulting in a power loss of 0.5-0.7W at a charging current of 1A, leading to low charging efficiency, typically only 78-82%; on the other hand, the reverse leakage current of ordinary diodes is usually in the range of 30-50μA, continuously consuming battery energy at night or on cloudy days. According to actual measurement data, a 1000mAh battery will lose approximately 3.5% of its capacity during 30 days of overnight rest. More seriously, the reverse leakage current of some low-cost diodes increases sharply under high-temperature environments, potentially reaching the milliampere level, accelerating battery discharge. Furthermore, the single-diode scheme lacks redundancy protection; once the diode fails, a large amount of battery energy will flow back to the photovoltaic panel, not only wasting energy but also potentially damaging the photovoltaic panel.

[0004] Secondly, traditional switching charging modules often lack effective noise suppression measures. Buck converter topologies generate significant voltage spikes and high-frequency ringing during switching transitions, with typical spike voltages reaching 5-8V and ringing frequencies ranging from several hundred kHz to several MHz. This high-frequency noise interferes with surrounding circuits through both conduction and radiation. Particularly when charging battery packs with a Battery Management System (BMS), high-frequency noise can easily couple to the BMS's sampling circuitry, leading to voltage and current measurement errors, and even triggering malfunctions in the BMS's overvoltage and overcurrent protection. Statistics show that the BMS false trigger rate is as high as 8.5% when using traditional charging modules, seriously affecting the safety and stability of charging. Furthermore, unsuppressed EMI radiation can interfere with nearby communication equipment, sensors, and other sensitive electronic devices, with radiation intensity in the 9kHz-30MHz frequency band often exceeding industry standard limits.

[0005] Secondly, regarding charging control accuracy, existing chargers generally employ low-precision current detection schemes. A common practice is to use ordinary resistors of 0.1-0.2Ω for current sampling, with resistance accuracy typically around 5% and a temperature coefficient as high as 200-500ppm / ℃. This low-precision detection results in charging current control accuracy of only ±10-15%, which further deteriorates with changes in ambient temperature. Inaccurate charging control can lead to overcharging or undercharging: overcharging accelerates battery aging and shortens lifespan; undercharging fails to fully utilize battery capacity, reducing system range. Experiments show that with a charging accuracy of ±15%, lithium batteries experience a 35% capacity decay after 1000 charge-discharge cycles, while precise control can reduce this decay to below 20%.

[0006] Furthermore, many low-cost solar chargers lack maximum power point tracking (MPPT) functionality altogether, or employ only simple solutions such as fixed voltage methods. The lack of MPPT prevents the photovoltaic panels from operating at their optimal operating point, significantly reducing energy harvesting efficiency. Especially under low-light conditions (such as early morning / evening hours or cloudy days), the maximum power point of the photovoltaic panels will shift significantly, with energy losses reaching 30-40% in fixed-operation-point solutions. Even those chargers equipped with MPPT functionality often employ complex perturbation-observation or incremental conductance methods, requiring continuous MCU computation, increasing system cost and power consumption, and are prone to failure or oscillation under rapidly changing lighting conditions.

[0007] In summary, existing solar chargers have serious shortcomings in terms of backflow protection, noise suppression, charging accuracy, and MPPT efficiency, and can no longer meet the requirements of modern solar energy applications for high efficiency, high reliability, low noise, and high-precision charging control. Utility Model Content

[0008] The purpose of this invention is to provide a step-down charging module for a solar charger. This step-down charging module for a solar charger features high efficiency, high reliability, low noise, and high-precision charging control.

[0009] The above-mentioned technical objective of this utility model is achieved through the following technical solution: A step-down charging module for a solar charger includes: a photovoltaic input terminal (V-SOLAR); a multi-stage input filter network disposed at the photovoltaic input terminal, the multi-stage input filter network including a large-capacity capacitor (C37, C34) and a small-capacity capacitor (C16) connected in parallel; a P-channel MOSFET switch (Q3) connected to the photovoltaic input terminal; a first Schottky diode (D2) connected in series at the output terminal of the P-channel MOSFET switch (Q3); and a controller (U4) connected to the P-channel MOSFET switch (Q3) for controlling the P-channel MOSFET switch. The switching state of Q3 is off; a second Schottky diode (D1) is connected between the output terminal of the first Schottky diode (D2) and ground; an energy storage inductor (LX3) is connected between the output terminal of the first Schottky diode (D2) and the battery terminal; a current sampling resistor (RCS) is connected in series between the energy storage inductor (LX3) and the battery terminal; output filter capacitors (C32, C33) are connected between the battery terminal and ground; and an RC snubber network is connected between the output terminal of the first Schottky diode (D2) and ground, the RC snubber network including a resistor (R23) and a capacitor (C36).

[0010] The present invention is further configured to include an MPPT voltage divider network connected to the photovoltaic input terminal. The MPPT voltage divider network includes a first resistor (R20), a second resistor (R21), a third resistor (R22), and a filter capacitor (C35). The first resistor (R20) and the second resistor (R21) are connected in series to form a voltage divider, and the third resistor (R22) and the filter capacitor (C35) constitute a filter circuit.

[0011] The present invention is further configured such that the resistance ratio of the first resistor (R20) and the second resistor (R21) is set so that the photovoltaic operating point is maintained within 70%-80% of the open circuit voltage.

[0012] The present invention is further configured such that the controller (U4) includes a BAT pin, a CSP pin, an MPPT pin, a DRV pin, and a VG pin. The BAT pin is connected to the battery terminal, the CSP pin is connected to the current sampling resistor (RCS), the MPPT pin is connected to the MPPT voltage divider network, and the DRV pin and VG pin are connected to the gate of the P-channel MOSFET switch (Q3).

[0013] The present invention is further configured such that the current sampling resistor (RCS) is a high-precision low-value resistor with a resistance of 0.05Ω and an accuracy of 1%.

[0014] The present invention is further configured such that the resistor (R23) in the RC absorption network has a resistance of 4.7Ω and the capacitor (C36) has a capacitance of 2.2nF.

[0015] The present invention is further configured such that the inductance value of the energy storage inductor (LX3) is 22μH.

[0016] The present invention is further configured such that the controller (U4) also includes a charging status indicator pin (CHRG, DONE), which is an open-drain output used to drive an indicator light or connect to an external controller.

[0017] The present invention is further configured such that a P-channel MOSFET switch (Q3) and a first Schottky diode (D2) are connected in series to form a double-layer anti-backflow protection structure to prevent battery power from flowing back to the photovoltaic panel.

[0018] In summary, this utility model has the following beneficial effects: 1. High-efficiency energy transfer: This invention uses a P-channel MOSFET switch (Q3) as the high-side switch, replacing the traditional series diode, significantly reducing the on-state voltage drop (Vds is approximately 0.05-0.1V, far lower than the 0.5-0.7V of a diode). This design reduces power loss by 0.4-0.6W and improves system efficiency by approximately 5-10% under a 1A charging current. Furthermore, a voltage divider network formed by the first resistor (R20) and the second resistor (R21) enables a simplified MPPT function where the photovoltaic panel operates at approximately 70-80% of its open-circuit voltage, increasing energy harvesting by 15-25% under different lighting conditions, with particularly significant effects under low-light conditions. This high-efficiency design achieves an overall system efficiency of 85-92%, far exceeding the 50-70% of traditional linear chargers.

[0019] 2. Dual-layer anti-backflow protection: This invention employs a dual-layer anti-backflow structure consisting of a P-channel MOSFET switch (Q3) and a first Schottky diode (D2) connected in series, forming a highly reliable protection mechanism. At night or when the battery voltage is higher than the panel voltage, Q3 quickly turns off; simultaneously, D2 provides additional unidirectional blocking, preventing backflow from the battery to the photovoltaic panel even in the event of Q3 control malfunction. This dual-layer protection structure effectively extends battery life, prevents unnecessary energy loss, and significantly improves the system's reliability in harsh environments.

[0020] 3. Low noise design: This invention incorporates an RC absorption network consisting of a resistor (R23) and a capacitor (C36) into the power circuit, which is directly connected between the output terminal of the first Schottky diode (D2) and ground, effectively suppressing high-frequency ringing and voltage spikes at the switching node.

[0021] 4. High-precision charging control: This invention uses a high-precision low-value resistor RCS with a resistance of 0.05Ω and an accuracy of 1% as the current sampling element. Combined with the precise comparator threshold inside the controller (U4), it achieves charging current accuracy control within ±3%, far superior to the ±10-15% of traditional chargers. This high-precision current control effectively protects the battery, preventing overcharging and charging overcurrent, and extending battery life. Simultaneously, the controller (U4) automatically implements a multi-stage charging process: MPPT → constant current (CC) → constant voltage (CV) → full charge / trickle charge, precisely controlling charging parameters and further optimizing the charging process. Attached Figure Description

[0022] Figure 1 This is the overall circuit schematic diagram of this utility model. Detailed Implementation

[0023] In the description of this utility model, it should be noted that directional terms such as "up", "down", "front", "back", "left", and "right" are used only for the convenience of describing and understanding this utility model, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0024] like Figure 1 As shown, this utility model provides a solar charger step-down charging module. This module adopts an asynchronous step-down Buck topology and is mainly used for direct charging applications of single-cell lithium / lithium iron batteries or small lead-acid batteries via photovoltaic panels. The module includes a photovoltaic input terminal (V-SOLAR), which is used to connect to a solar panel to receive electrical energy converted from solar energy.

[0025] A multi-stage input filtering network is installed at the photovoltaic input terminal (V-SOLAR), which includes large-capacity capacitors (C37, C34) and small-capacity capacitors (C16) connected in parallel. Specifically, C37 and C34 are both 22μF electrolytic capacitors, and C16 is a 0.1μF ceramic capacitor. This three-stage decoupling design (large, medium, and small) provides spectrum coverage, with the large-capacity capacitors handling low-frequency ripple and the small-capacity high-frequency capacitors handling high-frequency noise, effectively suppressing various types of ripple introduced by the photovoltaic panel and connecting cables.

[0026] A P-channel MOSFET switch (Q3), model FDS4435BZ, is connected to the photovoltaic input terminal (V-SOLAR). Its gate is connected to the DRV drive pin and VG reference pin of the controller (U4), its source is connected to the photovoltaic input terminal (V-SOLAR), and its drain is connected in series with a first Schottky diode (D2). The first Schottky diode (D2), model SS1045, has its anode connected to the drain of Q3 and its cathode connected to the switching node. The P-channel MOSFET switch (Q3) and the first Schottky diode (D2) connected in series form a double-layer anti-backflow protection structure, effectively preventing battery power from flowing back to the photovoltaic panel. During the day when there is sufficient sunlight, the controller (U4) drives Q3 to conduct, and current flows from the photovoltaic panel to the battery; at night or when the battery voltage is higher than the panel voltage, the controller turns off Q3 to prevent reverse current.

[0027] The controller (U4) uses the CN3791 chip and is the core control unit of the entire module. The controller (U4) includes multiple functional pins: the VCC pin (pin 9) is connected to the battery terminal to sample the battery voltage; the CSP pin (pin 8) is connected to the current sampling resistor (RCS) to detect the charging current; the MPPT pin (pin 6) is connected to the MPPT voltage divider network; and the DRV pin (pin 10) and VG pin (pin 1) are connected to the gate of the P-channel MOSFET switch (Q3) to control its switching state.

[0028] A second Schottky diode (D1), also an SS1045 type, is connected between the output terminal of the first Schottky diode (D2) and ground. The cathode of the second Schottky diode (D1) is connected to the switching node, and the anode is grounded, serving as the freewheeling diode for the Buck circuit. When the P-channel MOSFET switch (Q3) is turned off, the current in the energy storage inductor (LX3) freewheels through D1, maintaining the continuity of the inductor current.

[0029] An energy storage inductor (LX3) with an inductance of 22μH is connected between the output terminal of the first Schottky diode (D2) and the battery terminal. The energy storage inductor (LX3) is the energy storage element of the Buck converter circuit, storing energy when Q3 is on and releasing energy when Q3 is off. A current sampling resistor (RCS) is connected in series between the energy storage inductor (LX3) and the battery terminal. This resistor is a high-precision, low-value resistor with a resistance of 0.05Ω and an accuracy of 1%. The current sampling resistor (RCS) is used to accurately detect the charging current; the voltage difference across it is detected by the CSP pin of the controller (U4) and serves as the basis for constant current charging control.

[0030] Output filter capacitors (C32 and C33), both 22μF, are connected between the battery terminal and ground to reduce voltage ripple at the battery terminal and provide a stable charging voltage. Additionally, an RC snubber network, consisting of a resistor (R23) and a capacitor (C36), is connected between the output terminal of the first Schottky diode (D2) and ground. The resistor (R23) has a resistance of 4.7Ω, and the capacitor (C36) has a capacitance of 2.2nF. The RC snubber network is positioned close to the switching node and D1 to effectively absorb high-frequency energy generated during switching, suppress switching spikes and ringing, and reduce EMI interference.

[0031] This invention also includes an MPPT voltage divider network connected to the photovoltaic input terminal. This network consists of a first resistor (R20), a second resistor (R21), a third resistor (R22), and a filter capacitor (C35). The first resistor (R20) has a resistance of 140kΩ, and the second resistor (R21) has a resistance of 51kΩ. They are connected in series to form a voltage divider, which is connected to the MPPT pin of the controller (U4). The third resistor (R22) has a resistance of 120Ω and, together with the filter capacitor (C35) (220nF), forms a filter circuit, which is connected to the COM pin of the controller (U4). This MPPT voltage divider network achieves simplified Voc-K proportional maximum power point tracking, keeping the photovoltaic panel's operating point within 70%-80% of the open-circuit voltage, close to the maximum power point, thus improving energy harvesting efficiency.

[0032] The controller (U4) also includes charging status indicator pins (CHRG, DONE). The charging status indicator pins (CHRG is pin 3, DONE is pin 4) are open-drain outputs, which can directly drive LED indicators or be connected to an external controller to provide charging status indication.

[0033] The working process of this utility model is as follows: The photovoltaic panel generates electrical energy under sunlight. After ripple is filtered out by a multi-stage input filter network, the energy is transmitted to the Buck main circuit through a P-channel MOSFET switch (Q3) and a first Schottky diode (D2). The controller (U4) controls the duty cycle of the P-channel MOSFET switch (Q3) based on the reference voltage provided by the MPPT voltage divider network, ensuring the photovoltaic panel operates near its maximum power point. When Q3 is on, current flows from the photovoltaic panel through Q3, D2, LX3, and RCS to the battery, while LX3 stores energy. When Q3 is off, LX3 releases energy, and the current freewheels through D1. Throughout the process, the RC absorption network (R23, C36) effectively suppresses switching spikes and reduces EMI interference. The controller (U4) automatically implements a multi-stage charging process—MPPT → constant current (CC) → constant voltage (CV) → full charge / trickle charge—by detecting the battery voltage (BAT pin) and charging current (CSP pin), and displays the current charging status through charging status indicator pins (CHRG, DONE).

[0034] Through the above structural design and workflow, this utility model achieves high efficiency, high reliability, low noise and high precision solar charging function, and is particularly suitable for solar power supply scenarios such as small off-grid equipment, road signs, and data acquisition terminals.

[0035] To verify the above-mentioned technical effects, the present invention has set up the following experiment for verification: 1. A comparative testing method was used to directly compare the module of this utility model with a traditional solar charger. The testing equipment included: a precision power analyzer (±0.1% accuracy), a high-precision oscilloscope (500MHz bandwidth), an EMI test receiver (9kHz-30MHz), a battery charge / discharge testing system, and an adjustable intensity simulated solar light source. The testing environment included standard laboratory conditions (25℃, 45%RH) and harsh environmental conditions (-10℃~45℃, day / night cycle, periodic light variations). Ten modules of this utility model and ten traditional modules using a single diode for backfeed prevention were selected as samples. Each test was repeated 20 times to ensure data reliability.

[0036] 2. Technical Effect Comparison Table 3. Verification Conclusion Experimental results show that the solar charger step-down charging module of this invention outperforms traditional technologies in all performance indicators, as detailed below: (1) In the energy conversion efficiency test, the design of the P-channel MOSFET switch (Q3) combined with the first Schottky diode (D2) enables the energy conversion efficiency to reach 85-92%, which is 8-12% higher than the traditional single diode solution. When the charging current of 1A is tested under standard conditions, the power loss of the module of this utility model is reduced by 0.4-0.6W, which can significantly extend the battery life in long-term operation.

[0037] (2) The backflow prevention performance test shows that the double-layer backflow prevention structure of this utility model controls the nighttime backflow current to below 1μA, which is more than 98% lower than the 30-50μA of the traditional solution. In a 30-day nighttime static test for a 1000mAh battery, the traditional module caused a battery power loss of about 3.5%, while the module of this utility model only caused a loss of 0.07%, effectively solving the energy backflow problem in solar energy applications.

[0038] (3) EMI suppression tests demonstrate that the RC absorption network (R23=4.7Ω, C36=2.2nF) reduces the peak voltage of the switching node from 5-8V to 2-3V, a reduction of 60%. Frequency domain analysis shows that EMI radiation is reduced by an average of 12dB in the 9kHz-30MHz frequency band, with particularly significant suppression in the 100kHz-1MHz frequency band. This improvement allows the module of this invention to directly charge battery packs with BMS, reducing the BMS false trigger rate from 8.5% in traditional modules to below 0.3%.

[0039] (4) Charging accuracy test shows that the current sampling scheme using a 0.05Ω / 1% precision resistor controls the charging current accuracy within ±3%, which is far superior to the ±10-15% of the traditional scheme. After 1000 charge-discharge cycle tests, the battery capacity retention rate of the module of this utility model is 15% higher than that of the traditional module, effectively extending the battery life.

[0040] (5) Under low light conditions (10-30% standard light), the Voc-K ratio method MPPT of this invention improves the energy acquisition efficiency by 20-25%, which is particularly suitable for solar energy applications in the early morning, late evening and cloudy conditions, and greatly enhances the system's all-weather working capability.

[0041] In summary, this invention comprehensively improves the performance and reliability of solar charging systems, providing a high-efficiency and high-reliability charging solution for applications such as small off-grid devices, road signs, and data acquisition terminals, and has broad application prospects.

Claims

1. A solar charger step-down charging module, characterized in that, include: Photovoltaic input terminal (V-SOLAR); A multi-stage input filter network is provided at the photovoltaic input terminal, the multi-stage input filter network including a large-capacity capacitor (C37, C34) and a small-capacity capacitor (C16) connected in parallel; A P-channel MOSFET switch (Q3) connected to the photovoltaic input terminal; A first Schottky diode (D2) is connected in series at the output terminal of the P-channel MOSFET switch (Q3); A controller (U4) connected to the P-channel MOSFET switch (Q3) is used to control the switching state of the P-channel MOSFET switch (Q3); A second Schottky diode (D1) is connected between the output terminal of the first Schottky diode (D2) and ground; An energy storage inductor (LX3) is connected between the output terminal of the first Schottky diode (D2) and the battery terminal; A current sampling resistor (RCS) is connected in series between the energy storage inductor (LX3) and the battery terminal; Output filter capacitors (C32, C33) connected between the battery terminal and ground; An RC snubber network is connected between the output terminal of the first Schottky diode (D2) and ground. The RC snubber network includes a resistor (R23) and a capacitor (C36).

2. The solar charger step-down charging module according to claim 1, characterized in that, Also includes: An MPPT voltage divider network connected to the photovoltaic input terminal includes a first resistor (R20), a second resistor (R21), a third resistor (R22), and a filter capacitor (C35). The first resistor (R20) and the second resistor (R21) are connected in series to form a voltage divider, and the third resistor (R22) and the filter capacitor (C35) constitute a filter circuit.

3. The solar charger step-down charging module according to claim 2, characterized in that, The resistance ratio of the first resistor (R20) and the second resistor (R21) is set so that the photovoltaic operating point is maintained within 70%-80% of the open circuit voltage.

4. The solar charger step-down charging module according to claim 1, characterized in that, The controller (U4) includes a BAT pin, a CSP pin, an MPPT pin, a DRV pin, and a VG pin. The BAT pin is connected to the battery terminal, the CSP pin is connected to the current sampling resistor (RCS), the MPPT pin is connected to the MPPT voltage divider network, and the DRV pin and the VG pin are connected to the gate of the P-channel MOSFET switch (Q3).

5. The solar charger step-down charging module according to claim 1, characterized in that, The current sampling resistor (RCS) is a high-precision, low-value resistor with a resistance of 0.05Ω and an accuracy of 1%.

6. The solar charger step-down charging module according to claim 1, characterized in that, The resistor (R23) in the RC absorption network has a resistance of 4.7Ω and the capacitor (C36) has a capacitance of 2.2nF.

7. The solar charger step-down charging module according to claim 1, characterized in that, The inductance value of the energy storage inductor (LX3) is 22μH.

8. The solar charger step-down charging module according to claim 1, characterized in that, The controller (U4) also includes charging status indicator pins (CHRG, DONE), which are open-drain outputs used to drive indicator lights or connect to an external controller.

9. The solar charger step-down charging module according to claim 1, characterized in that, The P-channel MOSFET switch (Q3) and the first Schottky diode (D2) are connected in series to form a double-layer anti-backflow protection structure to prevent battery power from flowing back to the photovoltaic panel.

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