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Introduced a solar powered high-brightness white LED flash circuit
updatetime£º2008-11-19  Hits£º3221  
    

Abstract: A solar-powered high-brightness white LED flash circuit method, have a high value. Is the solar panels to charge batteries link the realization of programmes and flash control circuit design and high-brightness white LED on the life of the issue analysis and training and to extend its service life of the solution, final adoption of low - Integration of the large number of IC power use, allowing the system to achieve low-power static stability and the use of purpose.  
 Key words: solar energy; white LED; flash circuit; low power consumption  
1 INTRODUCTION  
 This paper describes the flash equipment is on the highway when the speeding vehicle camera captures the auxiliary lighting.  According to field work requirements, the need for adequate lighting and sufficient sources of energy service life, this circuit using solar-powered batteries, Equipment therefore requested a static low-power characteristics.  Lamps and other equipment, compared to white LED with high brightness, low power consumption, long life and other advantages. This paper will be specific to a solar-powered high-brightness white LED lights flashing circuit design, described the power supply circuit design and the realization of low-power static methods, and discuss the design process should pay attention to the problem.  
 2 system components  
 Figure l-based system block diagram of the composition.  Figure 1 below on the charge of the protection circuit, the flash control circuit of the white LED part of the protection circuit.  

 2.1 solar charging protection circuit  
 2.1.1 solar panels  
 Solar panels to provide power not only during the day and at night can also provide electricity.  Solar panels with the transistor, the semiconductor components, the main material is silicon, there are also some other alloy.  
 Solar panels on the surface by two different nature of the components.  When irradiated by the light, be able to change solar energy to electricity, the current flows from the other side.  
 Solar panels as long as the sun or the lights by the exposure, the general will be issued by the reception of light energy equivalent to 1 / 10 of power.  In order to make solar panels to minimize light reflection, light into electrical energy, usually in the top to prevent light casts a reflection of the film, so that solar panels on the surface was purple.  
 Solar power supply from the main part of solar panels (PV modules), and battery charging circuit components.  PV modules absorb light in the daytime, the solar energy into electricity stored in the solar cells within.  Generally sunny time, in an ideal light intensity, full of power as long as four hours.  The system uses 15 V solar panels, the actual measured at both ends of the battery-power supply voltage of 17 V ~ 20V, the charge current to 200 mA ~ 800mA.  
 2.1.2 battery design capacity  
 Solar power system is the main energy storage device battery.  And solar batteries are usually square supporting the work of the Fu Chong state, with the square of its voltage generating capacity and electricity consumption load varies.  Its load capacity than the much more electricity.  Battery power also affected by the temperature of the environment.  To solar cells match for long battery life and work of maintaining simple.  
 (1) the selection of batteries  
 Can and solar cells supporting the use of many types of batteries, widely used in a maintenance-free lead-acid batteries, lead-acid batteries Ordinary alkaline and nickel-cadmium battery of three.At present, the domestic use of lead-acid battery maintenance-free, because of its inherent "free" maintenance of less pollution and environmental characteristics, very suitable for reliable performance of the solar power system, in particular the unattended workstations.  Ordinary lead-acid batteries due to the need for regular maintenance and greater environmental pollution, mainly suitable for a maintenance capacity or use low-grade occasions.  Although the basic nickel-cadmium batteries are better low temperature, the charge, the performance-but because of their higher prices, only available at a special occasion.  
(2) battery capacity of calculation  
Battery capacity to ensure continuous power supply is very important. In 2001, the square generating capacity of each month are very different.  Phalanx of generating capacity can not meet the electricity needs of the month, we must give up battery power in the electricity needs over the month, is relying on battery power will be redundant store.  So square generating capacity and lack of surplus value, is to determine the basis for one of the battery capacity.  Similarly, the continuous rainy days during the load of electricity from the battery must also be made.  Therefore, the power consumption during the battery capacity is also identified one of the factors.  
 Therefore, the battery capacity Bc is calculated as follows:   
 Where: A for the safety factor, from between 1.1 to 1.4;  
 QL for the load on the average electricity consumption, to work on the current multiplied by the number of work hours;  
 NL for the longest continuous rainy days;  
 To amend the temperature coefficient, in general 0 ¡æ for more than l, -10% from more than 1.1, -10 ¡æ following from 1.2;  
 Cc for the battery discharge depth, 0.75 general admission lead-acid batteries, nickel-cadmium batteries for basic 0.85.  
 Under the system requirements, adopted, the choice of 12 V8Ah ordinary lead-acid batteries.  
 2.1.3 charging protection circuit  
 Solar charging protection from the circuit and over-charge protection composed of two parts.  
 Have sufficient protection: When the solar panels to charge batteries, battery 14.5 V output voltage, the charge Road relay control to stop charging solar panels.  Battery output voltage drop to 14 V, the solar panels to charge the batteries.  
 Over-protection: When the battery output voltage below 10.5 V, the battery power to stop the field circuit.10.5 V battery voltage, circuit re-supply from outside.  
¡£ Charging protection by the two operational amplifier circuit components, circuit shown in Figure 2. Figure 2 Vi1, Vi2 were battery output voltage, Vref compared to the operational amplifier reference, its value in accordance with the specific requirements set by the user.  In the actual design process, attention should be paid in Figure 2 feedback resistor selection, the greater resistance feedback, control output corresponding to the input Vi back to the smaller margin.  

 2.2 flash control circuit  
 Control circuits in accordance with different requirements for different designs.  The flash function in the complex control circuits can be used MCU MCU control, control of such convenient, simple and stable.  As the design of the system only requires regular flash flicker, a single function, the use of simple pure hardware circuits.  Circuit as shown in Figure 3.  

 2.2.1 pulse circuit  
0.5mA)¡£ The circuit pulse generator by 4047, 4047 external structure is simple, stable performance, but still very low power consumption (measured as static 0.5 mA).4047, as the output signal frequency circuit at the trigger pulse, the frequency of its output signals from an external capacitors and resistors control.  
 2.2.2-frequency circuits  
 The circuit used 14 2 hexadecimal calculator 4020 to achieve.  By 4047 the output of pulses as 4020 pulse input signal so that the 4020 count to 2-band, to the frequency purpose.  Characterized as a 14-frequency output, depending on the design requirements for different output, and static power consumption of 1 mA.  
2.2.3-steady-state trigger circuit  
 Steady-circuit triggered by the combination of a simple flip-flop, but the stability of the circuit design low power consumption and relatively large.  To avoid these shortcomings, this system uses integrated chip 4538.4538 trigger for the fringe circuit, according to the input signal can be different, set for the rising edge and falling edge trigger trigger.  In this system, the 4020 output signal 4538 as the input pulse, a steady-state single-trigger, the output pulse width from the external capacitors and resistors control, output pulse cycle from 4020 Pulse input provided by the frequency decision.  Finally, from 4538 output of the signal output LED light switches as the control signal.  
 This section of the main features of the design for use in full-scale integration devices, to achieve stability and high-power static small purpose.  
 2.3 White LED protection circuit  
 2.3.1 white LED Profile  
 White LED is the most favored LED new products, in lighting the development of the market potential should be looking forward to.  Tungsten Lamp for incandescent and fluorescent lamps and compared, LED is small in size (more than, the various combination), low heat (no heat radiation), the power consumption of small (low voltage, low current start), long life (10,000 Hours), reaction speed (in high frequency operation), green (seismic impact resistant not broken, recyclable waste, no pollution), the package can be flat and easy to develop into light products, and other advantages of short, no incandescent bulbs Gao Haodian, fragile and fluorescent waste mercury pollution problem, and other flaws, is optimistic about the industry in the next lO the year, replaced the traditional lighting apparatus of a potential commodity.  
 2.3.2 white LED performance analysis  
 (1) white LED colors, the wavelength of the real launch of the white LED does not exist.  This device is very difficult to manufacture, because the LED is characterized by only a wavelength of emission. Does not appear in the white color of the spectrum; An alternative approach is to use different wavelengths of light white.  
 White LED used in the design of a tip.  Blu-ray emission in the InGaN base material is covered conversion materials, such material incentives in the Blu-ray will be issued yellow light.¡£ Blu-ray and therefore has a mixture of yellow light, appears to the naked eye is white, Figure 4 for LED lighting sent the wavelength and forward current diagram. ÓÉ Can be seen from Figure 4: White LED emission wavelength (solid line), including blue and yellow light region of the peak, but appear to the naked eye is white. The relatively light sensitivity of the naked eye (dotted line) shown in Figure 4.  
 However, the technology used InGaN LED does not like the standard green, red and yellow light as easy to control.  InGaN LED display wavelength (color) will change as the forward current (as shown in Figure 5).  For example, the white LED colors presented by the changes arising from the conversion of different concentrations, and the blue LED forward voltage InGaN materials with the changes arising from wavelength change, however, the use of InGaN LED technology is not like the standard green, red Light and yellow light as easy to control.  InGaNLED show that the wavelength (color) will change as the forward current (as shown in Figure 5). For example, the white LED presented by the color changes arising from the conversion of different concentrations, and the blue LED forward voltage InGaN materials with the changes arising from changes in wavelength.  
 When forward current up to 10 mA, the forward voltage of the great changes.  Changes in the range of approximately 800 mV (Some models will be even greater changes in diode).  Discharge the battery voltage caused by the change will change color because of a change in voltage forward current.  In 10 mA forward current, forward voltage of about 3.4 V (with the numerical providers will vary scope 3.1 V ~ 4.0V). Similarly, between the different LED current - voltage characteristics have greater differences.  The direct use of battery-powered LED is very difficult, because the great majority of the battery will discharge with less than LED voltage so that the necessary minimum is wizard-voltage.  
 (2) white LED voltammograms of current and temperature change of  
 Figure 6 and 7, respectively LED voltammetry curve and the current temperature curve.  LED by the principle of luminescence can know, the white LED brightness changes is mainly determined by its current electricity.  

 From above white LED analysis can be seen:  
 (1) white LED current will affect the power of its wavelength change;  
(2) When the LED work in the current of 10 mA to 30 mA region, LED ends of the small changes in voltage, current will occur more changes  
 (3) LED under the scope of current with increasing temperature and smaller.  
 In order to make white LED long-term stability, take the following measures:  
 (1) opened two LED spacing, to achieve cooling purposes;  
 (2) the constant current power supply so that the white LED wavelength and in a constant state of brightness.  
 Can be drawn from the above analysis, in order to maintain a fixed LED brightness and luminous colors, and extend their working life, forward current must be maintained at a stable value, the constant current measures taken to ensure the stability of LED work.  
2.3.3 constant current protection circuit  
 This system will be the largest CMOS Current as electronic switches, circuit and a constant current to the LED array Constant-current power supply, the LED lamps can be prolonged stability. Here are constant current method.  
 Figure 8 for the most basic principle of constant circuit, plans to load resistance in RL (real for the LED array), Ro sampling for the resistance, Eg for the reference voltage, output current Io = Eg / Ro, that steady flow of power supply Current output voltage from the baseline sampling resistor and Ro Eg decision, Eg Ro and a determined, steady flow of output current from the power supply voltage and load out the effect of maintaining stability. ¡£ So, in order to obtain a stable output current, to provide an accurate baseline resistor voltage and sampling.  
This system under the basic principle of using CMOS FET and a constant current components of the basic operational amplifier circuit. ¡£ In this system, the reference voltage Eg by the control circuit in 4538 after the output pulse regulator circuit (using TL431 regulator). ¡£ Whenever the 4538 output is a pulse, will trigger constant circuit operational amplifiers, so that LED lit, to the effect of constant flash.  
 3 Conclusion  
 After testing, the static power circuit system for 5 mA ~ 7mA, with lower power consumption and high static stability.  Different users in accordance with the design requirements, through the revision of some of these parts to meet the design requirements.

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