Road emergency device charged by solar energy

Abstract

The utility model discloses a solar charging road emergency device, which relates to the technical field of solar charging equipment, and comprises a solar battery and is characterized in that the input end of a BUCK step-down circuit is electrically connected with the solar battery, the output end of the BUCK step-down circuit is electrically connected with a lithium battery protection circuit, and the lithium battery protection circuit is electrically connected with a lithium battery; the BOOST circuit is electrically connected with the lithium battery protection circuit; the LDO voltage reduction circuit is electrically connected with the lithium battery protection circuit, and the output end of the LDO voltage reduction circuit is electrically connected with the single-chip microcomputer. According to the utility model, the BUCK step-down circuit is used for reducing the voltage of the solar cell and charging the lithium battery, and when the sun is weak, the BOOST circuit is used for boosting the voltage of the solar cell and normally supplying the subsequent voltage, and the low voltage is boosted to the voltage meeting the charging requirement of the lithium battery and normally supplying the subsequent voltage. The electric quantity stored by the lithium battery is improved, and sufficient electric power is provided for emergency equipment in the emergency situation of a road.

Description

Technical Field

[0001] The utility model relates to the technical field of solar charging equipment, in particular to a road emergency device for solar charging. Background Art

[0002] Solar energy is a renewable energy source that is free and abundant, does not require transportation, and does not pollute the environment. It has created a new way of life for humans, and has brought society and humans into an era of energy conservation and pollution reduction.

[0003] In road emergencies, emergency power equipment is needed to power some road safety hazards. Emergency power equipment is generally composed of batteries, and solar energy just meets the charging needs, saving public electricity waste.

[0004] At present, in the existing batteries, once the power of the solar panel cannot meet the required output power, the voltage of the solar panel will be pulled down and the power will be cut off and restarted, causing the battery to fail to reach the maximum storage capacity, resulting in unnecessary impacts due to insufficient power in emergency situations. Utility Model Content

[0005] The purpose of the utility model is to provide a solar-powered road emergency device to address the deficiencies of the prior art, so as to solve the problem in the prior art that the conversion efficiency and power conversion efficiency are low, resulting in low output efficiency of the solar panel.

[0006] The utility model specifically provides the following technical solutions: a solar-powered road emergency device, comprising a solar cell, a voltage adjustment unit and a controller connected in sequence, wherein the voltage adjustment unit comprises:

[0007] A BUCK step-down circuit, wherein the input end is electrically connected to the solar cell, the output end is electrically connected to a lithium battery protection circuit, and the lithium battery protection circuit is electrically connected to a lithium battery;

[0008] A BOOST boost circuit, the input end of which is electrically connected to the lithium battery protection circuit, and the output end of which is connected to the emergency equipment through an external interface;

[0009] The input end of the LDO buck circuit is electrically connected to the lithium battery protection circuit, and the output end of the LDO buck circuit is electrically connected to the controller, and the controller is connected to the BOOST boost circuit.

[0010] Preferably, the BUCK step-down circuit supports MPPT solar maximum power point tracking and wide voltage input.

[0011] Preferably, a USB interface is provided between the output end and the emergency device.

[0012] Preferably, the solar cell has parameters of 6V and 2W.

[0013] Preferably, the BUCK step-down circuit is a CN3791 chip, and the input voltage range is 4.5V to 28V.

[0014] Preferably, the BOOST boost circuit is a TPS61088 boost chip, and the input voltage range is 2.7V to 12.6V.

[0015] Preferably, the LDO step-down circuit comprises:

[0016] Operational amplifier;

[0017] The voltage-dividing sampling circuit comprises a resistor R1 and a resistor R2 connected in series, wherein a connecting end of the resistor R1 and the resistor R2 is connected to an inverting input end of an operational amplifier;

[0018] A reference voltage connected to the non-inverting input terminal of the operational amplifier;

[0019] The transistor adjustment circuit is connected to the output terminal of the operational amplifier.

[0020] Preferably, the output voltage of the LDO step-down circuit is 3.3V.

[0021] Compared with the prior art, the utility model has the following advantages:

[0022] When the utility model is working, it is charged through the solar cell, and the BUCK step-down circuit is used to step down the voltage of the solar cell to charge the lithium battery. The LDO step-down circuit provides a suitable voltage for the controller. When the sun is weak, the controller controls the BOOST step-up circuit to step up the voltage of the solar cell, and the low voltage is increased to a voltage that meets the charging voltage of the lithium battery, and the subsequent voltage is provided normally, thereby increasing the amount of electricity stored in the lithium battery and providing sufficient power for emergency equipment in road emergencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a hardware block diagram of the utility model;

[0024] Figure 2 It is a three-stage lithium battery charging curve diagram of the utility model;

[0025] Figure 3 This is the BUCK type buck topology schematic diagram of the utility model;

[0026] Figure 4 This is a lithium battery charging circuit diagram of the utility model;

[0027] Figure 5 This is the BOOST boost topology diagram of the utility model;

[0028] Figure 6 It is the BOOST circuit diagram of the utility model;

[0029] Figure 7 This is the power soft start principle diagram of the utility model;

[0030] Figure 8 This is the internal working principle diagram of the LDO of the utility model;

[0031] Fig. 9 This is the LDO connection diagram of the utility model. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions of the embodiments of the utility model in conjunction with the drawings in the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0033] like Figure 1 As shown, an embodiment of the utility model provides a solar-powered road emergency device, comprising a solar cell, a voltage adjustment unit and a controller connected in sequence, wherein the voltage adjustment unit comprises a BUCK buck circuit, a BOOST boost circuit and an LDO buck circuit. Among them, the BUCK buck circuit input end is electrically connected to the solar cell, the output end is electrically connected to a lithium battery protection circuit, and the lithium battery protection circuit is electrically connected to a lithium battery; the BOOST boost circuit is electrically connected to the lithium battery protection circuit, and the output end is connected to the emergency equipment through an external interface; the LDO buck circuit is electrically connected to the lithium battery protection circuit, and the output end of the LDO buck circuit is electrically connected to the controller (here is a single-chip microcomputer), and the controller is connected to the BOOST boost circuit. Emergency equipment includes but is not limited to emergency lights and emergency sockets. The emergency light can be a traffic light, a road sign or a lighting lamp.

[0034] Among them, the solar BUCK buck circuit is used to reduce the voltage of the solar cell and charge the single lithium battery in three stages. In order to improve the solar energy conversion efficiency and make the circuit compatible with more solar panels, the BUCK buck circuit in the utility model needs to support the MPPT solar maximum power point tracking function and wide voltage input function.

[0035] The lithium battery BOOST boost circuit boosts the voltage of the solar panel to a voltage suitable for charging the lithium battery when the sunlight is weak, and then cooperates with the fast charge protocol recognition circuit to dynamically adjust the output voltage.

[0036] The LDO buck circuit uses a low voltage difference LDO (linear buck) to provide a stable 3.3V DC power to the controller. The LDO buck circuit is used to step down the output voltage of the lithium battery to ensure the normal power supply of the controller and improve the output efficiency.

[0037] When the line resistance is only 0.5 ohms, the line loss of series and parallel connection differs by 1.1 W. After comprehensive consideration, a 6V, 2W solar panel is used for power supply.

[0038] BUCK step-down topology and lithium battery charging circuit design:

[0039] According to the requirements of the utility model, the single-cell lithium battery charging circuit needs to meet the requirements of wide voltage input and three-stage lithium battery charging. A single-cell lithium battery refers to a single-string lithium battery, not just one lithium battery. Multiple lithium batteries can be connected in parallel to meet the needs of increasing capacity.

[0040] from Figure 2 As shown in , the complete charging process of a lithium battery is divided into three stages (the latter two stages are mostly used in actual use).

[0041] Stage 1: Trickle charging.

[0042] When the battery voltage is very low (the typical value is lower than 66.5% of constant voltage charging, about 2.75V), the internal lithium ion activity is poor and the internal resistance is large, so it can only accept a smaller charging current (generally around 30 to 50mA). Otherwise, the battery is prone to heat and aging, which not only damages the battery life but also has potential safety issues. Therefore, this stage is called trickle charging.

[0043] The second stage: constant current charging.

[0044] When the battery voltage is higher than 2.8V, the lithium ion activity of the battery is fully activated and the internal resistance is small, so it can accept high current charging. At this stage, the maximum current charging can be set according to the lithium battery parameters to increase the charging speed.

[0045] The third stage: constant voltage charging.

[0046] That is, the charging voltage is constant (4.2V). During the constant voltage charging process, the charging current continues to decrease until the current is lower than a certain value (usually set by the charging management chip), and then charging stops. The reason for this process is to prevent the battery from overcharging and allow the lithium battery to store as much power as possible.

[0047] Through the analysis of the above requirements, CN3791, a domestic solar charging management IC, was finally selected in this utility model. It has the solar maximum power point tracking function (MPPT), the input voltage range is 4.5V to 28V, supports the three-stage charging mode of lithium batteries, and can set the constant current charging current and solar input voltage through resistors, and the maximum charging current can reach 4A. This chip adopts the BUCK buck topology. Let's take a look at the working principle of the BUCK buck topology.

[0048] like Figure 3 The figure shows the principle diagram of the BUCK buck topology. The BUCK buck topology has two working states. When the MOS tube is turned on, the diode cuts off the current through the MOS tube and the inductor to supply power to the output capacitor and the load respectively. At this time, the inductor stores the magnetic field. When the MOS tube is turned off, since the inductor current cannot change suddenly, the diode provides a freewheeling path to continue to supply power to the output capacitor and the load.

[0049] By changing the duty cycle of the PWM signal on the gate of the MOS tube, the output voltage can be changed and the output voltage of the topology can be calculated.

[0050] Figure 4 It is a lithium battery charging circuit (i.e., lithium battery protection circuit) designed according to the CN3791 data sheet. The maximum power point voltage is set by two resistors, R33 and R36. During the production process of the utility model, it is set to 6V solar energy.

[0051] The circuit sets the constant current charging current of the lithium battery through a resistor. There is a 120MV voltage reference inside the circuit, which is compared with the sampling resistor to make the charging current reach a constant current state.

[0052] The state that the solar cell will reach when it is in the best state (suitable temperature and sufficient sunlight). At the same time, the loss on the transmission line and the conversion efficiency of the BUCK circuit must also be considered. This is a complex calculation model. The simple method is to measure the data experimentally and use the data to reflect the actual working conditions of the system. In one day, we measured the charging current of multiple groups under different lighting conditions and found that the current fluctuation is still relatively large. Several groups of data are lower than 16% of constant current charging.

[0053] The change of current during the constant current charging process of lithium batteries has little effect on the changes of the battery. However, if the charging stage enters the third stage at this time, and the current change makes the charging current lower than 16% of the constant current stage, CN3791 will consider the charging to be completed and enter the charging end state.

[0054] Solar voltage stabilization charging:

[0055] The maximum voltage of the solar panel is 6V, but it is affected by the light intensity, and the voltage will be very low when the light is weak. Therefore, a boost circuit is needed to increase the low voltage to a voltage that meets the charging voltage of the lithium battery.

[0056] like Figure 5 As shown in the figure, it is a BOOST boost topology. When the switch is turned on, the diode is turned off, the current passes through the inductor, and the switch returns to the ground. In this process, the inductor stores the magnetic field. When the switch is not turned on, the diode is turned on. Since the inductor current cannot change suddenly, an induced electromotive force is generated and superimposed with the input voltage. The current passes through the diode to supply power to the output capacitor and the load. Under this condition, the output voltage Vout is always greater than the input voltage.

[0057] like Figure 6 As shown in the figure, TI's boost solution is used in the BOOST circuit, using a synchronous rectifier boost chip TPS61088. The chip has a minimum input voltage of 2.7V and a maximum output voltage of 12.6V. It has a 10A switching current capability and high power conversion efficiency. It can fully meet the voltage and current requirements of the fast charging protocol.

[0058] There are electrolytic capacitors in the power supply circuit. These capacitors can stabilize the power supply voltage and filter out high-frequency interference.

[0059] However, using a large number of capacitors in the power input circuit will bring difficulties to circuit design. At the moment of power-on, the capacitor voltage cannot change drastically, and the voltage across the capacitor rises slowly and exponentially, and the capacitor current phase leads the voltage by 90 degrees. At the moment of power-on, the capacitor is equivalent to a short circuit. At this time, the current in the circuit is very large, which will form a surge current. In heavy-load application scenarios, sparks will occur at the moment of power-on.

[0060] In order to solve the above problems, a soft-start power supply circuit is used. The function of this circuit is to suppress surge current when the circuit is powered on. When powered on, the circuit switches to a high-impedance state and uses a small current to charge the capacitor. When the capacitor voltage reaches a certain value, the capacitor shows its own capacitive reactance characteristics. At this time, the circuit switches to a low-impedance state and the circuit works normally.

[0061] The principle of power soft start is as follows Figure 7 As shown, when the power is on, the MOS is turned off. At this time, the current charges the capacitor through the 100Ω resistor. When the capacitor has a certain voltage, the control signal controls the MOS tube to turn on. At this time, the resistor is short-circuited and the circuit switches to a low impedance state to work normally.

[0062] Power management features:

[0063] In order to realize the power management function and the expansion of subsequent functions, the stm32 microcontroller is used in the design to realize functions such as power display, boost circuit enable, charging status indication, overcurrent protection, etc.

[0064] The supply voltage range of the STM32F1 series microcontroller is 2.0 to 3.6V, while the maximum voltage of the lithium battery is 4.2V. The lithium battery cannot be used directly to power the microcontroller, and a voltage conversion is required here.

[0065] Compared with switching power supplies, linear power supplies have low conversion efficiency and high heat generation when the voltage difference is high. Usually, linear power supplies are not used in high voltage difference and high current conversion. In this application, the maximum voltage of the lithium battery is 4.2V. At this time, the power conversion efficiency of LDO is 78%. When the battery voltage is 3.5V, the conversion efficiency can be as high as 94%. In this utility model, the conversion efficiency is acceptable. Let's take a look at the basic working principle of LDO linear power supply.

[0066] Figure 8 The internal working principle diagram of LDO consists of four parts: voltage divider sampling circuit, reference voltage, error amplifier circuit, and transistor adjustment circuit. The reference circuit provides a stable reference voltage Vref input to the non-inverting input of the operational amplifier (error amplifier circuit). The voltage divider sampling circuit is composed of two high-precision resistors R1 and R2 in series, and the sampling voltage is fed back to the inverting input of the operational amplifier. According to the basic working principle of the operational amplifier, the operational amplifier will automatically adjust the output voltage so that the voltage of its non-inverting input terminal is equal to that of its reverse input terminal (virtual short). At this time, the output voltage of LDO can be calculated by the following formula. The voltage obtained by the voltage divider sampling circuit is compared with the reference voltage, and the difference (error) between the two is amplified.

[0067] When the transistor in the LDO is turned on, the C pole and the E pole are equivalent to a resistor. When there is current, a voltage drop will be generated on the transistor. Therefore, the output voltage of the LDO is always lower than the input voltage. The voltage drop of different buck chips will also be different. For example, the internal transistor voltage drop of the common LM7805 chip is 2V, which requires the input voltage to be greater than 7V to ensure the normal operation of the chip. According to the output of the error amplifier circuit, its conduction degree is adjusted to control the current passing through the regulator and stabilize the output voltage.

[0068] In the utility model, the voltage difference between the battery voltage and the microcontroller power supply voltage is low, so when selecting the LDO chip, a chip with a large voltage difference cannot be selected. Here, a low voltage difference LDO chip SC662K is used.

[0069] The input-output voltage difference of SC662K is only 0.2V. When the lithium battery voltage is higher than 3.5V, SC662K can work normally and provide a stable 3.3V voltage. The voltage range of STM32F0 series microcontrollers is 2.0~3.6V. When the voltage is lower than 3.5V, lithium batteries can be used directly for power supply. During the period of direct battery power supply, the AD reference voltage in the microcontroller is no longer 3.3V. In order to obtain the current reference voltage of ADC, the 1.224V stable voltage source inside the microcontroller can be used to calculate the microcontroller power supply voltage at this time to calculate the microcontroller reference voltage. Therefore, when the battery voltage is lower than 3.5V, directly using the battery for power supply will not affect the normal operation of the microcontroller ADC. Fig. 9 This is the LDO connection diagram.

[0070] The above content is a further detailed description of the utility model in combination with a specific preferred implementation mode. For technicians in the technical field to which the utility model belongs, they can make several simple deductions or substitutions without departing from the concept of the utility model, which should be regarded as belonging to the protection scope of the utility model.

Claims

1. A solar-powered road emergency device, characterized in that: The invention comprises a solar cell, a voltage adjustment unit and a controller connected in sequence, wherein the voltage adjustment unit comprises: A BUCK step-down circuit, wherein the input end is electrically connected to the solar cell, the output end is electrically connected to a lithium battery protection circuit, and the lithium battery protection circuit is electrically connected to a lithium battery; A BOOST boost circuit, the input end of which is electrically connected to the lithium battery protection circuit, and the output end of which is connected to the emergency equipment; The input end of the LDO buck circuit is electrically connected to the lithium battery protection circuit, and the output end of the LDO buck circuit is electrically connected to the controller, and the controller is connected to the BOOST boost circuit.

2. A solar-powered road emergency device as claimed in claim 1, characterized in that: The BUCK step-down circuit supports MPPT solar maximum power point tracking and wide voltage input.

3. A solar-powered road emergency device as claimed in claim 1, characterized in that: A USB interface is provided between the output end and the emergency device.

4. A solar-powered road emergency device as claimed in claim 1, characterized in that: The solar cell has parameters of 6V and 2W.

5. A solar-powered road emergency device as claimed in claim 1, characterized in that: The BUCK step-down circuit is a CN3791 chip, and the input voltage range is 4.5V to 28V.

6. A solar-powered road emergency device as claimed in claim 1, characterized in that: The BOOST boost circuit is a TPS61088 boost chip, and the input voltage range is 2.7V to 12.6V.

7. A solar-powered road emergency device as claimed in claim 1, characterized in that: The LDO step-down circuit comprises: Operational amplifier; The voltage-dividing sampling circuit comprises a resistor R1 and a resistor R2 connected in series, wherein a connecting end of the resistor R1 and the resistor R2 is connected to an inverting input end of an operational amplifier; A reference voltage connected to the non-inverting input terminal of the operational amplifier; The transistor adjustment circuit is connected to the output terminal of the operational amplifier.

8. A solar-powered road emergency device as claimed in claim 1, characterized in that: The output voltage of the LDO step-down circuit is 3.3V.

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