High-efficiency charging circuit for nickel-metal hydride battery

Abstract

The utility model provides an efficient charging circuit for a nickel-metal hydride battery, which belongs to the technical field of charging circuits, and comprises a DCDC charging circuit, a current sampling conversion circuit and a voltage hysteresis charging control circuit, a Celloon XL4001 step-down DCDC converter with a constant current loop is selected, and an external Schottky diode TS1 is added to play a follow current role; the charging voltage is conveniently adjusted according to the resistance values of the R7 and R10 resistors; the current sampling conversion circuit adopts a battery high-side sampling mode, so that the situation that the output voltage of the battery drops too much due to too large voltage drop of a sampling resistor during low-end sampling during battery power supply is avoided; the operational amplifier introduces a sampling differential voltage signal into a current detection pin of the XL4001; temperature adjusting design is introduced into hysteresis design, reverse change is carried out along with the temperature, then the upper limit value and the lower limit value of hysteresis charging voltage are changed, and the defect that a traditional nickel-metal hydride battery charging circuit has adverse effects on the service life of a battery is overcome.

Description

Technical Field

[0001] The utility model belongs to the technical field of charging circuits, and more specifically, relates to a high-efficiency charging circuit for nickel-metal hydride batteries. Background Art

[0002] In the current field of power collection terminal devices, nickel-metal hydride batteries, as a common backup power source, are widely used in various devices. Such devices usually need to continue operating when the external power supply is interrupted to complete key tasks such as data storage and event reporting. However, there are many problems with existing nickel-metal hydride battery charging solutions. Traditional constant-current charging solutions often rely on voltage regulator components to build a constant-current circuit, which results in a limited charging current. Especially in the initial stage of charging, a large charging current may cause the transistor to overheat, affecting the stability and safety of the device. In addition, as a backup power source, if the nickel-metal hydride battery is not charged and discharged regularly for a long time, the performance and lifespan of the battery will be affected. Therefore, it is particularly important to charge and discharge the battery regularly.

[0003] To overcome the above problems, many researchers have been committed to developing more efficient and energy-saving charging solutions. However, most of the current solutions on the market fail to take into account both the performance and service life of the battery and perform poorly in high-temperature environments. The charging process under high-temperature conditions easily causes the evaporation of the electrolyte inside the battery, thereby reducing the battery performance and shortening its service life. Therefore, finding a charging solution that can improve charging efficiency and adapt to different environmental conditions has become an urgent problem to be solved. Summary of the Utility Model

[0004] In view of this, the utility model provides a high-efficiency charging circuit for nickel-metal hydride batteries, which solves the drawbacks that the charging current of the traditional nickel-metal hydride battery charging circuit is not easily too large, and an excessive charging current will cause serious heating of the transistor for regulating charging in the initial stage of charging, which has an adverse effect on the lifespan of the battery.

[0005] The utility model is implemented as follows:

[0006] The present utility model provides an efficient charging circuit for nickel-metal hydride batteries, which includes a DCDC charging circuit, a current sampling and conversion circuit, a voltage hysteresis charging control circuit, and resistors. There are twenty-two resistors, namely the first resistor to the twenty-second resistor. The DCDC charging circuit is provided with a main control chip and the sixth resistor to the tenth resistor. A Schottky diode is arranged outside the main control chip, and the output port of the main control chip is connected to the Schottky diode. The Schottky diode functions as a freewheeling diode. The charging voltage of the DCDC charging circuit is achieved by adjusting the resistance values of the seventh resistor and the tenth resistor. The current sampling and conversion circuit is provided with an operational amplifier and the first resistor to the fifth resistor. The operational amplifier introduces the sampled differential voltage signal into the current detection pin of the main control chip for adjusting the constant current output. The sixth resistor and the ninth resistor of the current sampling and conversion circuit are used for current sampling. The sixth resistor serves as a sampling resistor, and both ends of the sampling resistor are connected to both sides of the differential input of the operational amplifier. The voltage hysteresis charging control circuit is provided with an NTC thermistor and the eleventh resistor to the twenty-second resistor;

[0007] The main control chip is a non-synchronous DCDC converter.

[0008] 1. The main control chip XL4001, a step-down DCDC converter of Xinlong.

[0009] 2. The operational amplifier LM358A, a dual-channel general operational amplifier of Sirep.

[0010] 3. The current sampling and conversion circuit.

[0011] 4. The voltage hysteresis charging control circuit.

[0012] A total of twenty-two resistors are provided. Among them, the current sampling and conversion circuit includes the first resistor to the fifth resistor, the DCDC charging circuit includes the sixth resistor to the tenth resistor, and the voltage hysteresis charging control circuit includes the eleventh resistor to the twenty-second resistor.

[0013] The present utility model only uses several discrete components, including basic components such as the XL4001 DC-DC converter, Schottky diode, resistors, and operational amplifiers, which greatly reduces the manufacturing cost. Compared with the traditional complex charging circuit, the present utility model does not require an expensive dedicated charging management chip, effectively controlling the production cost and facilitating the market promotion and popularization of the product.

[0014] Based on the above technical solution, an efficient charging circuit for nickel-metal hydride batteries of the present utility model can also be improved as follows:

[0015] Among them, the DCDC charging circuit adopts the battery high-side sampling method.

[0016] Further, the B_CS signal output by the operational amplifier is the voltage signal across the sampling resistor and is input to the 5th pin of the main control chip.

[0017] Further, the NTC thermistor includes a first thermistor and a second thermistor. The first thermistor and the second thermistor are connected to the positive input terminal of the hysteresis comparator. The characteristics of the first thermistor and the second thermistor are that their resistance values decrease as the temperature increases. By this characteristic, the upper and lower voltage thresholds of the hysteresis comparator are changed.

[0018] The beneficial effects of adopting the above improvement scheme are as follows: The present utility model takes into account the actual use environmental factors and particularly adds a temperature adjustment mechanism. By introducing the NTC thermistor, the upper and lower limits of the charging voltage can be automatically adjusted according to the change of the ambient temperature, preventing overcharging or over-discharging of the battery under high temperature conditions and further extending the service life of the battery. In a high temperature environment, the battery is easily damaged, and the electrolyte is easily volatilized, which may lead to a decline in battery performance or even damage. The present utility model ensures the safe charging of the battery at different temperatures by adjusting the hysteresis voltage range, guaranteeing the safety of users and the stability of the battery.

[0019] Further, the change of the upper and lower voltage thresholds of the hysteresis comparator is specifically as follows: The higher the temperature, the upper threshold and the lower threshold of the corresponding hysteresis charging voltage will decrease by a predetermined amplitude.

[0020] Further, for the high-efficiency charging circuit: The battery is charged at a constant current. When it reaches the upper threshold moment of the hysteresis charging voltage, the operational amplifier outputs a low level. At this time, the enable pin of the main control chip is pulled high, and the main control chip does not work.

[0021] The beneficial effects of adopting the above improvement scheme are as follows: The present utility model adopts a constant current charging method, ensuring less energy loss during the charging process. The XL4001 DC-DC converter has high conversion performance and can charge the battery at a constant current, thereby reducing unnecessary energy loss and improving energy utilization efficiency. At the same time, by reasonably setting the charging current value, a fast and stable charging process is achieved, which helps to extend the battery life.

[0022] Further, for the high-efficiency charging circuit: When the battery self-discharges to the lower threshold value of the hysteresis charging voltage, the operational amplifier outputs a high level. At this time, the enable pin of the main control chip is pulled low, and the main control chip is in a working state and continues to charge the battery.

[0023] Further, the charging current of the battery is 155 mA.

[0024] The Schottky diode TS1 is mainly used as a freewheeling diode in the buck topology and can be selected according to the actual charging current. In this solution, the charging current is 155 mA. Considering the interval design requirements, a diode with a larger current rating can be selected, such as the SS14 (the freewheeling current can reach 1 A).

[0025] Furthermore, the main control chip is specifically the charging management chip XL4001.

[0026] Furthermore, the operational amplifier is specifically the operational amplifier LM358A, a Silergy dual-channel general-purpose operational amplifier.

[0027] Compared with the prior art, the beneficial effects of the nickel-metal hydride battery high-efficiency charging circuit provided by the present utility model are as follows:

[0028] Low cost: Only a few discrete components are used, such as basic components like the XL4001 DC-DC converter, Schottky diode, resistors, and operational amplifiers, which greatly reduces the manufacturing cost and is conducive to the market promotion and popularization of the product;

[0029] High charging efficiency: The constant-current charging method is adopted to ensure less energy loss during the charging process. The XL4001 DC-DC converter has high conversion performance and can charge the battery at a constant current, improving the energy utilization rate. At the same time, by reasonably setting the charging current value, a fast and stable charging process is achieved, which helps to extend the battery life;

[0030] Prevent battery passivation: Through the reasonable design of the current sampling and conversion circuit, the battery charging status is monitored in real time, avoiding the battery being in an undercharged or over-discharged state for a long time, and effectively preventing the occurrence of battery passivation. This is crucial for improving the overall performance and service life of the battery. Especially in the case of long-term use, it can significantly reduce the risk of battery capacity attenuation;

[0031] Temperature-adjusted charging voltage: The present utility model takes into account the actual use environment factors and particularly adds a temperature adjustment mechanism. By introducing an NTC thermistor, the upper and lower limits of the charging voltage can be automatically adjusted according to the change of the ambient temperature, preventing overcharging or over-discharging of the battery under high-temperature conditions and further extending the service life of the battery. In a high-temperature environment, the battery is easily damaged, the electrolyte is volatile, which may lead to a decline in battery performance or even damage. The present utility model ensures the safe charging of the battery at different temperatures by adjusting the hysteresis voltage range, guaranteeing user safety and battery stability. Description of the Drawings

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for the description of the embodiments of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 It is a DCDC charging circuit diagram of a high-efficiency charging circuit for a nickel-metal hydride battery;

[0034] Figure 2 It is a current sampling conversion circuit diagram of a high-efficiency charging circuit for a nickel-metal hydride battery;

[0035] Figure 3 It is a voltage hysteresis charging control circuit diagram of a high-efficiency charging circuit for a nickel-metal hydride battery;

[0036] In the drawings, the list of components represented by each label is as follows:

[0037] 10. Main control chip; 11. Schottky diode; 21. First thermistor; 22. Second thermistor. Specific embodiments

[0038] To make the purpose, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention.

[0039] As Figure 1 、 Figure 2 、 Figure 3 shown, it is the first embodiment of a high-efficiency charging circuit for a nickel-metal hydride battery provided by the present invention. In this embodiment, it includes a DCDC charging circuit, a current sampling conversion circuit, a voltage hysteresis charging control circuit, and resistors. There are twenty-two resistors, namely the first resistor to the twenty-second resistor. The DCDC charging circuit is provided with a main control chip 10 and the sixth resistor to the tenth resistor. A Schottky diode 11 is arranged outside the main control chip 10. The output port of the main control chip 10 is connected to the Schottky diode 11. The Schottky diode 11 plays a freewheeling role. The charging voltage of the DCDC charging circuit is realized by adjusting the resistance values of the seventh resistor and the tenth resistor. The current sampling conversion circuit is provided with an operational amplifier and the first resistor to the fifth resistor. The operational amplifier introduces the sampled differential voltage signal into the current detection pin of the main control chip 10 for adjusting the constant current output. The sixth resistor and the ninth resistor of the current sampling conversion circuit are used for current sampling. The sixth resistor serves as the sampling resistor, and both ends of the sampling resistor are connected to both sides of the differential input of the operational amplifier; the voltage hysteresis charging control circuit is provided with an NTC thermistor and the eleventh resistor to the twenty-second resistor;

[0040] The main control chip 10 is a non-synchronous DCDC converter.

[0041] When in use, a total of 22 resistors are set, which are R1, R2, R3......R21, R22 in sequence;

[0042] The FB pin of the main control chip serves as the voltage feedback pin of the charging management chip, with a reference voltage of 1.235V. The seventh resistor, namely R7, and the tenth resistor, namely R10, serve as the voltage-dividing resistors for feedback adjustment. For example, R7 = 100k and R10 = 22k. The charging voltage is V = (1.235 / 22k) * (100k + 22k) = 6.84V. After a 0.7V diode voltage drop, the battery charging cut-off voltage is about 6.1V.

[0043] The sixth resistor, namely R6, and the ninth resistor, namely R9, are current sampling resistors. For example, at this time, R6 is selected as a 1R resistor and R9 is not soldered. At this time, according to the output current calculation, I = 0.155V / 1R = 155mA.

[0044] The main function of the current sampling conversion circuit is to sample the voltages on both sides of the current sampling resistor (R6), and then feedback to the current sampling pin of the charging chip, achieving the purpose of dynamically adjusting the current. The two ends of the sampling resistor are connected to both sides of the differential input of the operational amplifier, as Figure 2 shown. "Both sides" refers to the two input terminals of the operational amplifier - the non-inverting input terminal and the inverting input terminal. One end of the sampling resistor is connected to the non-inverting input terminal of the operational amplifier, and the other end is connected to the inverting input terminal of the operational amplifier. The purpose of doing this is to enable the operational amplifier to measure the voltages on these two input terminals simultaneously, and then determine the state of its output signal based on the relationship between these two voltages.

[0045] For conventional battery charging, the sampling resistor is placed on the negative side of the battery. This low-end sampling method has too high a voltage drop across the sampling resistor when the battery is powered (if the voltage drop across a 1R resistor is 1V when discharging 1A). High-end sampling can avoid this situation. The sampling resistor is placed in the charging circuit and has no impact on the discharging circuit. Here, the differential amplifier does not need to amplify the signal, but only converts the voltage across the sampling resistor into a voltage signal with respect to ground. As Figure 1 shown, the B_CS signal output by the operational amplifier is the voltage signal across the sampling resistor and is input to the 5th pin of the charging management chip.

[0046] Among them, in the above technical solution, the DCDC charging circuit adopts the battery high-side sampling method.

[0047] The DCDC charging circuit adopts the battery high-side sampling method. Here, it is mainly to avoid the too large voltage drop of the sampling resistor during low-side sampling when the battery is powered, which causes too much drop in the battery output voltage. Finally, the operational amplifier introduces the sampled differential voltage signal into the current detection pin of the XL4001 for regulating the constant current output. The battery high-side sampling method means that during the battery charging or discharging process, the position for sampling the battery current is selected at the positive terminal of the battery. This method is opposite to the traditional battery low-side sampling method, which usually samples the current at the negative terminal of the battery.

[0048] Further, in the above technical solution, the B_CS signal output by the operational amplifier is the voltage signal across the sampling resistor and is input to the 5th pin of the main control chip 10.

[0049] Further, in the above technical solution, the NTC thermistor includes a first thermistor 21 and a second thermistor 22. The first thermistor 21 and the second thermistor 22 are connected to the non-inverting input terminal of the hysteresis comparator. The characteristics of the first thermistor 21 and the second thermistor 22 are that the resistance value decreases with the increase of temperature, and the upper and lower limit voltage thresholds of the hysteresis comparator are changed through this characteristic.

[0050] Further, in the above technical solution, the change of the upper and lower limit voltage thresholds of the hysteresis comparator is specifically as follows: the higher the temperature, the upper threshold and the lower threshold of the corresponding hysteresis charging voltage will have a predetermined amplitude of decrease.

[0051] Further, in the above technical solution, for the high-efficiency charging circuit: when the battery is charged at a constant current until the upper threshold moment of the hysteresis charging voltage, the operational amplifier outputs a low level. At this time, the enable pin of the main control chip 10 is pulled high, and the main control chip 10 does not work.

[0052] "Enable" is an electronic engineering term, referring to the process of enabling or activating a certain function or module. In an electronic system, a specific pin (for example, the enable pin) is often used to control whether other parts work. When this pin is pulled high (that is, a high-level signal is received), it means that the relevant function is enabled or allowed to work. When the battery charging reaches the upper threshold of the hysteresis voltage, the operational amplifier outputs a low level. At this time, the enable pin of the charging management chip XL4001 is pulled high, which means that the charging management chip starts to work and initiates the charging process. In other words, when the enable pin is pulled high, the charging management chip starts to execute its function, that is, to control the charging process of the battery.

[0053] The hysteresis comparator has the following characteristics: when the input voltage reaches the threshold voltage from low to high, the output voltage jumps immediately. When the input voltage slowly increases from small to large, the output voltage is always high until the input voltage is greater than the upper threshold voltage of the hysteresis comparator (for how to calculate the specific threshold voltage, please refer to relevant technical literature), and then the output voltage becomes low. At this time, according to the principle of the circuit diagram, it can be seen that the triode V1 cannot reach the conduction condition, and the enable pin of the main control chip is at a high level through R11 (note that the enable function of XL4001 works at a low level and shuts down at a high level).

[0054] Further, in the above technical solution, for the high-efficiency charging circuit: when the battery self-discharges to the lower threshold value of the hysteresis charging voltage, the operational amplifier outputs a high level. At this time, the enable pin of the main control chip 10 is pulled low, and the main control chip 10 is in the working state and continues to charge the battery.

[0055] When the input voltage slowly changes from large to small, the output voltage is always low until the input voltage is less than the lower threshold voltage of the hysteresis comparator, and then the output voltage becomes high. At this time, according to the principle of the circuit diagram, it can be seen that the triode V1 reaches the conduction condition, and the enable pin of the main control chip is pulled low by the conduction of the triode V1. At this time, XL4001 works to charge the battery.

[0056] It means that the voltage of the battery has dropped below the set threshold. In this case, the enable pin of the main control chip will be pulled low. Here, the "enable pin" usually refers to an input pin used to turn on or off the chip function. When it is pulled low, it means that the main control chip will stop working or enter an energy-saving mode.

[0057] Further, in the above technical solution, the charging current of the battery is 155 mA.

[0058] The buck topology structure consists of a switching tube, a diode, an inductor, and a capacitor. The control loop generally uses a PWM (pulse width modulation) chip to control the duty cycle to determine the on and off of the switching tube. The function of the Buck circuit is to convert the DC voltage Vin into the DC voltage Vout to achieve the purpose of step-down.

[0059] Further, in the above technical solution, the main control chip 10 is specifically the charging management chip XL4001.

[0060] XL4001 is a step-down DCDC chip. XL4001 is a high-efficiency step-down DC-DC converter with a fixed 150KHz switching frequency, which can provide a maximum output current capacity of 2A, and has the characteristics of low ripple, excellent linear regulation rate and load regulation rate. XL4001 integrates a fixed-frequency oscillator and a frequency compensation circuit, which simplifies the circuit design.

[0061] Further, in the above technical solution, the operational amplifier is specifically the operational amplifier LM358A, a Silergy dual-channel general operational amplifier.

[0062] Specifically, the principle of the present utility model is as follows:

[0063] The XL4001 DC-DC converter is a non-synchronous DCDC converter. Its input terminal is connected to the power supply, and its output terminal is connected to the battery interface. The Schottky diode TS1 is used for freewheeling, and the charging voltage can be achieved by adjusting the resistance values of the resistors R7 and R10. The resistors R6 and R9 are used for current sampling, and the operational amplifier introduces the sampled differential voltage signal into the current detection pin of the XL4001. The NTC thermistors RT1 and RT2 are connected to the positive-phase input terminal of the hysteresis comparator. As the temperature rises, their resistance values decrease, changing the upper and lower limit voltage thresholds of the hysteresis comparator. The battery is charged efficiently at a constant current of 155 mA. When the charging reaches the upper threshold of the hysteresis voltage, the operational amplifier outputs a low level, and at this time, the enable pin of the charging management chip XL4001 is pulled high. When the battery self-discharges slowly and drops to the lower threshold, the operational amplifier outputs a high level, and the enable pin of the charging management chip XL4001 is pulled low. By repeating this cycle, the efficient charging and protection of the battery are achieved.

[0064] In summary, the present utility model makes full use of the characteristics of the XL4001 DC-DC converter, combines the current sampling conversion circuit and the hysteresis charging design with temperature adjustment, and realizes various advantages such as low cost, high efficiency, anti-passivation, and temperature-controlled charging.

Claims

1. An efficient charging circuit for a nickel-metal hydride battery, characterized in that, It includes a DCDC charging circuit, a current sampling and conversion circuit, a voltage hysteresis charging control circuit and resistors. There are twenty-two resistors, namely the first resistor to the twenty-second resistor. The DCDC charging circuit is provided with a main control chip (10) and the sixth resistor to the tenth resistor. A Schottky diode (11) is arranged outside the main control chip (10). The output port of the main control chip (10) is connected to the Schottky diode (11). The Schottky diode (11) plays a freewheeling role. The charging voltage of the DCDC charging circuit is realized by adjusting the resistance values of the seventh resistor and the tenth resistor. The current sampling and conversion circuit is provided with an operational amplifier and the first resistor to the fifth resistor. The operational amplifier introduces the sampled differential voltage signal into the current detection pin of the main control chip (10) for adjusting the constant current output. The sixth resistor and the ninth resistor of the current sampling and conversion circuit are used for current sampling. The sixth resistor serves as the sampling resistor. Both ends of the sampling resistor are connected to both sides of the differential input of the operational amplifier; The voltage hysteresis charging control circuit is provided with an NTC thermistor and the eleventh resistor to the twenty-second resistor; The main control chip (10) is a non-synchronous DCDC converter.

2. The high-efficiency charging circuit for a nickel-metal hydride battery according to claim 1, wherein, The DCDC charging circuit adopts the battery high-side sampling method.

3. The high-efficiency charging circuit for a nickel-metal hydride battery according to claim 2, wherein The B_CS signal output by the operational amplifier is the voltage signal across the sampling resistor and is input to the 5th pin of the main control chip (10).

4. The high-efficiency charging circuit for a nickel-metal hydride battery according to claim 3, wherein The NTC thermistor includes a first thermistor (21) and a second thermistor (22). The first thermistor (21) and the second thermistor (22) are connected to the positive-phase input terminal of the hysteresis comparator. The first thermistor (21) and the second thermistor (22) are characterized in that their resistance values decrease with the increase of temperature. The upper and lower limit voltage thresholds of the hysteresis comparator are changed through this characteristic.

5. The high-efficiency charging circuit of a nickel-metal hydride battery according to claim 4, characterized in that The change of the upper and lower limit voltage thresholds of the hysteresis comparator is specifically as follows: the higher the temperature, the upper and lower limits of the corresponding hysteresis charging voltage will decrease by a predetermined amplitude.

6. The high-efficiency charging circuit of a nickel-metal hydride battery according to claim 5, characterized in that, For the high-efficiency charging circuit: the battery is charged at a constant current. When it reaches the upper limit moment of the hysteresis charging voltage, the operational amplifier outputs a low level. At this time, the enable pin of the main control chip (10) is pulled high and the main control chip (10) does not work.

7. The high-efficiency charging circuit of a nickel-metal hydride battery according to claim 6, characterized in that, For the high-efficiency charging circuit: when the battery discharges itself to reach the lower limit value of the hysteresis charging voltage, the operational amplifier outputs a high level. At this time, the enable pin of the main control chip (10) is pulled low and the main control chip (10) is in the working state and continues to charge the battery.

8. An efficient charging circuit for a nickel-metal hydride battery according to claim 7, characterized in that, The charging current of the battery is 155 mA.

9. The high-efficiency charging circuit of a nickel-metal hydride battery according to claim 8, characterized in that The main control chip (10) is specifically the charging management chip XL4001.

10. An efficient charging circuit for a nickel-metal hydride battery according to claim 9, characterized in that, The operational amplifier is specifically the operational amplifier LM358A, a Silergy dual-channel general-purpose operational amplifier.

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