Design and implementation of the hottest super cap

2022-08-07
  • Detail

With the development of economy and the progress of society, people have put forward higher and higher requirements for energy. Looking for new energy has become an urgent task facing mankind. Solar power generation is considered to be the most important energy in the 21st century because of its incomparable cleanness, safety, universality and sufficiency of resources compared with thermal power, hydropower and nuclear power. The storage of solar energy is the key to the development of solar energy products. At present, various batteries are mainly used. However, the long charging time, short service life and non environmental protection of batteries have always been the bottleneck of the development of solar energy products. As a kind of fast charging, long service life and green environmental protection energy storage element, supercapacitor has brought new and easily worn vitality to the development of solar energy products. This paper introduces in detail the design and implementation of a super capacitor solar lawn lamp. The lawn lamp well combines the advantages of solar energy and super capacitor. It can actively light up without installing other power supplies. It can also automatically control the switch of the lamp according to the intensity of the ambient light. It is easy to install, no wiring, stable and reliable, maintenance free, environment-friendly and pollution-free, and has a long service life. It can be widely used in square green space, community lawn and other places

design selection

a. selection of light source

due to the key breakthrough of LED technology, the performance price ratio has also been greatly improved. The current LED has a service life of more than 100 000h, and the working voltage is low. It is very suitable for solar lawn lamps. In addition, LED is powered by low-voltage DC. Its light source control cost is low. It can adjust the light and shade, and can be switched frequently. Moreover, it will not adversely affect the performance of LED. Therefore, considering the reliability, cost performance, color temperature and luminous efficiency, the super bright LED with rated voltage of 3.3 V and working current of 6 Ma can be selected as the light source in the design. As the lawn lamp not only has decorative function, but also has certain lighting function, it can be used with 8 LEDs

b. selection of solar cell

solar cell is a semiconductor device that converts solar energy into electrical energy according to the photovoltaic effect principle of semiconductor pn junction. It is the core device of supercapacitor solar lawn lamp. The performance of solar cells directly determines the energy conversion efficiency and the stability of output voltage, and also directly determines the performance of supercapacitor solar lawn lamp. Therefore, monocrystalline silicon solar cells with good cost performance should be used in the design

due to the difference between the annual total solar radiation and the average peak sunshine hours in various regions of the earth, the solar grass has other software in the computer system of the operation control software, which is related to the design of the operation platform lamp and the geographical location of the lamp. The relationship between the rated output power of the solar cell module and the input power of the lamp is about 2 ~ 4:1, The specific proportion shall be determined according to the daily working hours of the lamp and the lighting requirements for continuous rainy days. The power of the solar cell of the system is 3.3V × zero point zero zero six × 8=0.1584 --------- Nabing, Vice President/Professor w of Donghua University of technology. Assuming that the solar cell work efficiency is 40% and the effective working time is 5 hours a day, 3 W/6 V solar cells can be selected

c. selection of super capacitor

because the input energy of the solar cell is extremely unstable, and the lawn lamp only lights up when the surrounding light is weak, so it is necessary to configure the power storage system to work effectively when it can be loaded with Honda's off-road motorcycle. At present, lead-acid batteries, Ni Cd batteries or Ni-H batteries are widely used, but there are many defects in using batteries as power storage systems: firstly, rechargeable batteries have limited charging times (less than 1000 times) and short service life; Secondly, due to the influence of its chemical structure, it can not be charged with high current; Thirdly, the battery needs to have control circuits such as anti overcharge, anti discharge and temperature compensation, and the control circuit is more complex; Fourth, rechargeable batteries mainly use chemical reaction to charge and discharge. The waste in the batteries will pollute the environment and is not an environmental protection product

therefore, super capacitor is selected as energy storage element in this product. The capacitor has a very large capacity of farad level, a very strong charge holding capacity, a very small leakage current, and an 8-hour voltage drop rate of less than 5%; Without special charging circuit and control discharge circuit, it can be charged quickly and can be charged only at a state higher than its leakage current (the typical value is about 1 mA). Therefore, even in cloudy days, the solar cell can charge the supercapacitor; Compared with the battery, its overcharge and over discharge do not have a negative impact on its service life, with high reliability and long service life (the charge discharge cycle life is more than 100000 times); In addition, it has excellent temperature performance and can be used normally in the ambient temperature of -40 ℃ ~ 75 ℃; No pollution, a green power supply; It can be welded, and there are no problems such as weak contact like the battery

this solar lawn lamp product uses a 5.0V/225 f capacitor module composed of 6 2.5 V/150 f supercapacitors produced by Jinzhou Kemei Energy Co., Ltd. the ESR (DC) of a single capacitor product is only 20m Ω, with a diameter of 25 mm and a height of 48 mm. The charging time of 5 V/225 f super capacitor is (when the charging current is 450mA):

where: c-rated capacity of capacitor; △ u-change of working voltage of capacitor; I-capacitor charging current; T- capacitor charging time

discharge time of super capacitor:

where: ESR is the DC internal resistance of the capacitor. The 5 V/225 f supercapacitor can discharge from 5 V to 0.6 v

design of system control circuit

a. charging circuit

the charging circuit in this system is composed of anti overvoltage and anti reverse charging circuits. Figure 1 shows its charging circuit. Zd1 in the figure is a 5.6v zener diode. When the battery voltage is higher than 5.6 V, Q2 is on, and all the current of the silicon battery is consumed through resistance Q2. When the silicon battery voltage drops below 5.6 V, Q2 ends, and the silicon battery charges the super capacitor, And at the same time protect the super capacitor

the anti reverse charging control circuit can ensure that when the input voltage of the solar cell is lower than the super capacitor voltage, the super capacitor will not charge the solar cell in reverse, so as to avoid unnecessary energy loss. The reverse charging control can be completed by diode D1 in Figure 1. Schottky diode is selected as this diode because the conduction voltage drop of Schottky diode is lower than that of ordinary diode

b. driving LED voltage stabilizing circuit

since the rated voltage of the selected LED lamp is 3.3 V, while the voltage of the supercapacitor is 5.0 V, and the voltage of the supercapacitor will continuously decrease during discharge, a voltage stabilizing circuit is required to drive the LED

in this paper, a VFM switch type DC/DC boost voltage regulator with very low quiescent current manufactured by CMOS process is selected. The chip includes VFM control circuit, LX switch driving transistor, reference voltage unit, oscillator, error comparison amplifier, voltage sampling resistance, LX switch protection circuit, etc. Only one inductor, one output capacitor and one Schottky diode are needed outside the chip to provide stable low noise output voltage. The regulator has 8 μ A has the characteristics of extremely low input current, low ripple and low noise, the efficiency can reach 80%, and has an extremely low starting voltage of 0.6 V, and the output voltage accuracy can reach ± 2.5%. This part of the circuit is shown in Figure 2

the inductance and diode at the periphery of 331c will affect the conversion efficiency. In addition, the capacitance and inductance will also affect the output ripple. Therefore. Appropriate inductors, capacitors and Schottky diodes should be selected in the design to obtain higher conversion efficiency and lower ripple and noise. According to the data manual of 331c, this design selects 47 μ H and less than 0.5 Ω inductance and 47 μ F low ESR tantalum capacitor. Diodes used for rectification have a great impact on the efficiency of DC-DC. Although ordinary diodes can also make the DC-DC circuit work normally, they will reduce the efficiency of DC-DC converter by 5% ~ 10%. Therefore, D3 adopts Schottky diode ln5817 with low forward conduction voltage and short reaction time

c. light control circuit

super capacitor solar lawn lamp requires light control switch circuit to control the switch of LED. To light the LED when the ambient light is dim, and turn off the LED when the light is bright. Some light control switch circuits use photoresistors to switch LEDs, and solar cells can also be directly used as photosensitive switches, because the characteristics of solar cells are better than photoresistors. This part of the circuit is shown in Figure 3

in Figure 3, U1 is a six inverter 74hc14 with Schmitt trigger, in which the multivibrator is composed of the second inverter, R5 and C1. In this way, when the light is bright in the daytime, the solar cell voltage rises. Pin 1 of 74hc14 is high level, pin 2 of 74hc14 is low level, and pin 8 also outputs low level. The triode Q1 stops and the LED turns off. When the light turns dark and the solar cell voltage drops to a certain level, pin 1 of hc14 is at a low level and pin 2 of hc14 is at a high level. The multivibrator starts to oscillate and outputs high and low levels through Y4. Q2 is on and off. At this time, just adjust the values of R6 and C1 to adjust the flash frequency so that the human eye can not distinguish it. The greatest advantage of this is that it can prolong the working time of the lawn lamp. The actual test shows that the circuit can work continuously for more than 10 hours every day, and can fully meet the user's needs

conclusion

super capacitor and integrated DC-DC chip are used in the design of super capacitor solar lawn, so the whole circuit design is simple, high reliability, and belongs to green environmental protection products. At present, this design has been successfully applied to practical products

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