日期：2012年8月17日

rgb led flashlight and Xenon lamp

White LED Driver drive power limited xenon lamp flash to illuminate the shooting scene provides a cost-effective choice. This article describes the basic concept of xenon lamp, and the details of a typical low-power based on the ON Semiconductor NCP5007 chip, low-cost flash drive circuit design.

rgb led flashlight and Xenon lamp

Digital camera and is equipped with camera phones have new product into a mainstream product, these products within the digital image sensor based on CCD or CMOS technology. Able to support the image sensor in low light conditions, the flash circuit became necessary solutions for digital cameras, camera phones are becoming more common. Satisfy the flash requirements of the main light source is a xenon bulb and now the new high-brightness white LED lights.

The main advantage of the xenon lamp flash pulse generated by high power light output, while the advantages of the LED program is a relatively small size and thin, and longer conduction time in the video capture, the light output with the xenon lamp is only average compared. In particular, the xenon lamp flash pulse is very short, to enable the camera to capture photos made into a static picture. They need a special drive to produce high pressure and high energy storage capacitor to store electrical energy.

We found that the white LED panel driver to drive power limited xenon lamp flash to illuminate the shooting scene provides a cost-effective choice. This article describes the basic concepts of the xenon lamp, and details a typical low power / low-cost flash applications.

The xenon lamp has a glass enclosure at each end of an electrode, filled with low pressure rare gas mixtures. In the steady state, as shown in Figure 1, the voltage on the electrode is set lower than the trigger voltage. At this point, no current flows through, and the system remained stable until the trigger voltage applied to the third electrode. For the considered low-power light, this high-voltage pulse in the 1kV range, it comes with a small core transformer by a sudden discharge of the capacitor C2 is triggered.

The gas mixture is excited by plasma flash. For consumer applications, flash duration is 2ms. Flash type, the energy stored in the capacitor C1 can be as low as 1 joule (small camera), up to several thousand joules (professional application). Flash energy consumption shown in Equation 1:
Depending on the type of xenon lamp, the capacitor charging voltage is basically for 160V to 600V. The energy of low-power hand-held camera needs no more than a few joules, and the output voltage range of 160 to 250V. Higher voltages can be seen generally in a professional studio equipment used.
In addition to the DC voltage, high voltage pulse to excite the plasma in the bulb, high-intensity arc generated between both ends of the electrodes. Pulse amplitude depends on the type of lamp used in the system, ranging from lower 1.6kV to 10kV. Micro-xenon lamp is applied to the third external electrode of the lamp 1.6kV/5μs pulse triggers the pulse shown in Figure 2 for pulse transformer and high voltage capacitor connected arising. Charge the capacitor to the flash dc voltage (200V), and suddenly after the trigger button S1 to the pulse transformer primary side discharge. From the secondary side of high pressure is applied to the outer surface on the bulb, the flash is excited.
The main advantage of this concept is the light output and pulse duration is very short, quick photographs moving subject frozen at some point. The disadvantage of this design is the size of the storage capacitor, you need to board a higher voltage, and during filming capacitors need to be recharged (consumer applications, the charging time of 5-10 seconds).
According to the sensitivity of the imager and lens aperture in the general environment for consumer applications, a relatively small capacitance is sufficient to photograph in bright pictures. Therefore, you can use a simple converter to the battery voltage up to 200V voltage of the low-pressure xenon lamp required.

rgb led flood lights and white led driver

 

General white LED current is about 20mA, but the high brightness LED 200 to 300mA current. If your product requires three to four high-brightness white LED; brightness average general practice is to string them connected together. On the market, most of the white LED driver chip can only drive 20mA. Hit a series high current LED applications will have to think of other ways. Intersil’s EL7516 is a typical step-up chip. This chip operates at 1.2MHz fixed-frequency PWM mode, built-in 1.5A, 200mΩ MOSFETs. Figure 1 shows the EL7516 a typical circuit. DC-DC boost the role of EL7516 will be 2.7 ~ 5.5V input into a constant voltage of 12V. General PWM control chip, the FB pin is connected to the error amplifier is compared with 1.3V. R1, R2 resistor value is selected to set the output voltage.

With the development of white LED lights, it’s more widely applied. In the past, the white LED is the most common application is as a small-size color LCD backlight. White LED brightness increase, its application has spread to other areas; such as a flashlight or cell phone camera auxiliary lighting. The following describes a general boost chip to drive high current LEDs efficient circuit.

EL7516 lines of constant pressure to change the drive LED constant current circuit is very simple. Shown in Figure 2, the FB pin of R1 replaced by LED grow lights, change R2 can adjust the current through the LED. R2 values ​​selected from the following formula: R2 = VFB / IledVFB FB pin voltage; that 1.3VIled is the current through the LED

For example, if the requirements of Iled 300mA; then R2 needs to 4.3Ω.

On the circuit of Figure 3, the biggest drawback is the loss of R2. R2 by 300mA, the resistance of the power consumption is close to 0.39W. Such a great power not only affect the efficiency, we also need to use the relatively large size of the resistance to accept 0.39W heat. In general, these applications are battery powered. Efficiency and line PCB space requirements are more stringent, now let us look at how to improve the efficiency of this line.

egardless of the circuit changes how EL7516 will adjust the duty cycle so that the FB voltage to maintain 1.3V. The assumption D1 positive voltage drop is 0.6V, the voltage drop across R2 is about 0.7V. To maintain a 300mA LED current, R2 can be used to 2.3Ω. R2 power consumption also dropped from the original 0.39W 0.21W. Although the power consumption has been reduced, but R2 have to use a half-watt resistor to achieve this line.

rgb led flood lights and white led driver

A cheap TL431 added to the circuit as a 2.5V reference. As mentioned earlier, the EL7516 will remain FB 1.3V, the current through R4 is: (2.5-1.3) / 20k = 60uA. FB is a high-impedance pins, we assume that this 60? A full inflow of R5 and made the same 1.2V voltage drop. 0.1V, the rest of the R2 to complete. In order to facilitate the purchase, R2 is selected as 0.39Ω. So the current through the LED tube is about: 0.1/0.39 = 255mA. R2, power consumption is significantly reduced to: 0.1X0.255 = 26mW.

rgb led high power and led car use

The basic use of the controller reduces the cost of the car displays, signal and lighting electronic equipment. Switch adjustment circuit in the highest efficiency light LED to control the brightness of the lights.

Recently, LED tube has been replaced by low-voltage halogen technology, widely used in the car for general lighting. Design engineers have long life and low operating DC voltage LED lighting two advantages quickly gave approval.

On the other hand, in order to make these new LED technology to develop, you need to use more complex, more expensive vehicle electronic control system. The emergence of new ultra low-end 8-bit microcontroller (MCU), allowing design engineers can significantly reduce the cost and complexity of the system, use this alternative lighting solutions to be able to be profitable.

Due to the use of low-end MCU, high-brightness LED tunnel (HBLED) has developed many new applications, to continue to attract more users. New input, the HBLED including: monitor, car signs, lights, mobile devices and lighting equipment.

Overall, the LED has a nonlinear volt-ampere characteristic, the need for limiting the control of power consumption and light output of these two important factors. Power consumption and light output depends on the current drive the HBLED the ideal power is the constant current source. The high brightness LED lights, standard LED in its output power. Traditional LED output power is typically limited to below 50mW, but HBLED is able to provide 1-5W of output power.

Want to get the constant current source in many different ways, such as the use of series resistors, linear current source or switching regulator. The use of the switching regulator is the most common energy-saving solution. Switching regulator to cut off the input voltage, the duty cycle to control the average current, in order to achieve its current control – when the load requires a higher load current, the circuit connected to the time extension to fit the load current changes .

The HBLED the current is generated by the average power stored in the inductor L within. Switch is closed, the inductor will store energy as much as possible, the current flowing through the HBLED will be enhanced until it reaches the maximum or switch off. Then, when the switch is turned off, the energy stored in the inductor will provide HBLED current. This current will gradually weaken until you reach the minimum or switch is again closed.

rgb led high power and led car use

Current control to solve the problem becomes very simple, based on the the HBLED above the MCU controller dimming. Right the HBLED to implement dimming There are many different techniques, some of which may include the patent issues. Under any conditions, the dimmer on the same basis, namely: fully open in the HBLED the normal operating current HBLED period of time, and then completely to the continued closure of the period of time. Periodically at a faster rate to complete the action (the human eye can see) to give the impression HBLED light levels darken. The three techniques most commonly used are: pulse width modulation (PWM), frequency modulation and the bit angle modulation.

rgb led lamps and super bright led

Invented in the 1960s, it is the use of electrons and holes in semiconductor materials combined with each other and release energy, the energy band (Energy Gat,) rank changes, they release energy to light-emitting display. The LED has a small size, long life, low driving voltage, low power consumption, fast reaction rate, good shock resistance, it is widely used in the field of signal indicator, digital display. As technology continues to progress the development of ultra-bright LED has been successful, especially in the successful development of white LED lights, making it more and more used in the lantern decoration, and even the lighting in the area.

rgb led lamps and super bright led

l super bright LED features

Compared with the traditional lighting, ultra-bright LED has the following advantages:

1) long life, reliability and durability, very low maintenance costs LED can be used continuously 105h, 100 times longer than ordinary incandescent bulbs;

2) high-efficiency can already reach 201m / w. Expected by 2005 will reach 501m / W [1], the LED) the spectrum almost all concentrated in the visible light spectrum, and its luminous efficiency up to 80% ~ 90
%, LED energy-saving lamp energy saving but also 1/4;

3) color, light color simple example, 12 inches of red traffic lights, it uses low-efficiency 140W incandescent lamp as a light source, generated by 2000lm white The red filter, the light loss of 90%, leaving only under 2001m of red, 18 red LED light source lamp used in Lumileds Lighting Company, including circuit losses, consumes only 14W, and can produce the same luminous efficiency;

4) light speed fast car lights is an important area of ​​application of the LED light source, LED response speed (ns level), the high level LED brake lights, installed in the car can reduce rear-end accidents.

Bright LED in recent years has been in a car near light applications, such as the German Audi Audi A86.O, Italy Fioravanti concept car introduced at the 2003 Geneva Motor Show, the Yak, the U.S. Ford Motor Company recently at the Detroit Motor Show launched ModEL U are beginning to be bright LED used in the design of the headlamps.

Despite the ultra-bright LED has many advantages, but there are still the following shortcomings:

1) low power single LED tube market power generally in 5W following, not yet more high-power LED, which is the biggest bottleneck of LED difficult to become a lighting preferred;

2) the need to strictly control the temperature LED is a semiconductor material, with the diode as the PN junction diode highlight the power is relatively large, so the same with the power semiconductor devices, need to consider the problem of heat dissipation, junction temperature is too high will directly affect the LED life, and increased LED light decline in serious cases, the LED burned out;

3) the high price in addition to low power, the price is the main factor of the LED is difficult to become a lighting Although the LED has been most understanding, most people optimistic, but its high price is difficult to be accepted by consumers, the current single yellow LED about O. 6 yuan / month, green and blue single LED at about 1.8 yuan / the price of the white LED of about 2.2 to 5.5 yuan / month; dozens of single LED portfolio, the cost will greatly increase such as an LED installed in lawn lamp, the unit price is equivalent to general lawn several times, the LED to become a mainstream light source of lighting in the future, it must be moving in the direction of the large lumen, the cost of it be possible to reduce the market possible breakthrough.

Characteristics of the two super bright LED flood lights

HPWA-xH00 Lumileds Lighting Company, a super bright LED, it as an example the analysis of ultra-bright LED features. Figure 1 is the forward voltage drop (VF) and the forward current (IF) curve, the curve shows that when the forward voltage exceeds a certain threshold (about 2V), commonly referred to as the turn-on voltage can be approximated that , IF and VF is proportional to. Table 1 shows the electrical characteristics of the major super bright LED. Table 1 shows, the super bright LED’s highest IF up to 1A, VF is usually 3 ~~ 4V.