月份：2012年3月

Dimmable led street light is no longer a myth

 

Dimmable led street light is no longer a myth

 

Ever since mankind realized must do everything possible to energy conservation, in order to solve the pressing problems of atmospheric warming, how to reduce electricity for lighting as an important issue on the agenda. Because 20% of the total energy consumption of electricity for lighting. Fortunately, energy efficient dimmable led street light, the LED itself than more than five times that of incandescent lamp, energy-saving fluorescent lamps, energy-saving lamps also about twice, unlike fluorescent lamps, energy saving lamps as mercury. If you can take advantage of dimming to energy conservation, it is also very important means of energy-saving. But in the past all the light sources are not easy to achieve dimming and easy dimming is a great advantage of the dimmable led street light.

 

Because on many occasions, in fact, do not need to turn on the lights or at least not so bright, but very bright light, such as midnight to dawn hours of street lights; subway cars from the ground to open the car to the outskirts of the ground lights; more common in a sunny office near the window, schools, factories, such as fluorescent lamps are also opened there. These places every day do not know a waste of electricity! The past because of the high-pressure sodium lamps, fluorescent lamps, ceiling lamps, energy saving lamps cannot dimming, only to forget it. To switch to led high bay, you can freely adjust light, electrical energy can be saved! So for lamp dimming, the dimming is not the main applications of the family wall, the market is also very small. But demand dimming of street lights, offices, shopping malls, schools, factories, it is more important occasions, not only a huge market, and considerable energy saving. These occasions do not need manual dimming, but auto-dimming, intelligent light!

The future development for high efficiency led lighting

 

The future development for high efficiency led lighting

 

Have already said that the best LED dimming is a simple PWM generator PWM dimming using the PWM dimming can be installed in the wall switch, and then use a potentiometer to control the PWM dimming ratio in order to achieve. To bright light switch off, then you need to add a pair of lines. It is not compatible with the original wall of the high efficiency led lighting switch leads. The lead of the led high bay lighting technology switch is only 2, you can while dimming can switch. This advantage is difficult to be compatible. But actually, truly the most commonly used dimming lamps table lamp or floor lamp dimmer switch are installed on the power cord is not a wall, that just do not care to take advantage of the wall of the two leads. In other words, the tone of the PWM alone can be directly applied to Dimmable high efficiency led lighting.

 

Taiwan has a company launched four sections called the EZ-Dimming GM6182 switch tone light of high efficiency led lighting would be a good program. Only the use of ordinary light switch on the wall will be able to achieve the dimming, the first time open for all light, the second on 60% brightness, third on 40% brightness, the fourth open for 20% brightness. The advantage of this system can use an ordinary wall switch dimming. And the power factor more than 0.92. Did not produce interfering signals into account. The disadvantage cannot be continuous dimming. There are operational high efficiency led lighting problems.

The disadvantages of high intensity led lamp used in the house

 

The disadvantages of high intensity led lamp used in the house

 

1) high intensity led lamp is more than half a century old technology, it has many shortcomings explained above, is a long overdue elimination technology. It should be and incandescent lamps, halogen lamps and stage of history.

 

2) many of these chips claim has the PFC can improve the power factor, in fact, it only improves the load power factor as the high intensity led lamp, to make them look close to the pure resistance of incandescent and halogen lamps, and has not improved, including the power factor of the entire system, including the led high bay.

 

4) all of the LED dimming system are also to adjust the LED forward current, the existence of the previously described chromatographic offset shortcomings.

 

5) the installation of high intensity led lamp proportion of less than one ten thousandth, while the proportion of thyristor switches installed in the wall even one ten thousandth of the SCR dimming lamps not because the vast majority of the installation of SCR dimming are table lamps, bedside lamps, floor lamp. Moreover, There are dozens of different specifications of the SCR and transistor tone light switch, in fact the development of IC is impossible to compatible with all of the thyristor switch, but only compatible with a small part of.

 

6) high intensity led lamp is a new Genesis technology, it has incomparable superiority. There is no need to sacrifice the advantages of the LED in order to take care of the backward of other LED lighting products. Should not go to the wall of the newly installed SCR switch to LED dimming.

RGB dimmable LED down lights using SCR

 

RGB dimmable LED down lights using SCR

 

Ordinary incandescent and halogen lamps commonly used SCR to dimmer. Led high bay lights and RGB dimmable LED down lights is a pure resistance device, it does not require the input voltage sine wave, because the current waveform is always the same voltage waveform, so regardless of how the voltage waveform deviate from the sine wave, as long as the change of the valid values ​​of the input voltage, can be dimming. SCR of the AC sine wave to be cut to achieve change its valid values ​​for the purpose. Load and thyristor switch in series.

 

Change the variable resistor divider ratio can change the conduction angle, in order to achieve the purpose of change of RGB dimmable LED down lights valid values​​. Usually the potentiometer with a switch connected to the input of n for the light switch. In addition to the SCR, there are transistors along the dimming technology, because their basic problem is the same, not in this introduces.

 

SCR dimming the shortcomings and problems

However, SCR dimming range of issues.

1) SCR destruction of the sinusoidal waveforms, thereby reducing the power factor value, usually the PF is less than 0.5, and the conduction angle is smaller the worse the power factor (1/4 brightness only 0.25).

2) Similarly, the non-sinusoidal waveforms to increase the harmonic coefficients.

3) non-sinusoidal waveform line to cause serious interference signal (EMI)

 

Also produce unexpected problems, in the ordinary thyristor dimmer circuit output to the LED drive power for RGB dimmable LED down lights is input LC filter causes SCR oscillation, this oscillation is insignificant for the incandescent because the thermal inertia of the incandescent lamp makes the human eye do not see this oscillation.

AC power supplied LED dimming technology

 

AC power supplied LED dimming technology

 

How to achieve the PWM dimming

Concrete realization of the PWM dimming method in series with a MOS switch is in the LED load, the anode of the LED dimming technology with a constant current power supply.

Then added to the gate of the MOS transistor with a PWM signal to quickly switch the led high bay in order to achieve dimming. Also a lot of constant current chip itself with a PWM led high bay interface, you can directly receive the PWM signal, and then output to control the MOS switch. PWM dimming method are the advantages and disadvantages?

 

Eliminate the dimming caused by whistling: 200Hz or above the human eye cannot detect, but until 20kHz are human auditory range. At this time it is possible to hear the slightest sound. To solve this problem there are two ways, Firstly, increasing the switching frequency above 20kHz, out of the human auditory range. However, the frequency of LED dimming technology is too high can also cause some problems, because the impact of various parasitic causes the pulse waveform distortion (along the front and rear).This reduces the accuracy of dimming. Another method is to identify the sound device to be addressed. In fact, the main sound device output ceramic capacitors, ceramic capacitors are usually made ​​of high dielectric constant ceramic, these ceramics have piezoelectric properties. 200Hz pulse will produce a mechanical vibration and sound. The solution is the use of tantalum capacitors instead. However, the high voltage tantalum capacitors is difficult to obtain, but the price is very expensive, will increase the cost of LED dimming technology.

Change the brightness of the high intensity uv led

 

Change the brightness of the high intensity uv led

 

To work long hours at low brightness may make the step-down constant current source efficiency to reduce the temperature rise increased unable to work. Most people may think that just down to reduce the output power of constant-current source, so it can not cause the power consumption of high intensity uv led of the step-down constant current source to increase the temperature rise increased. Little do they know when the forward voltage drop caused by the lower forward current make buck than the lower. The efficiency of the step-down constant current source and high intensity uv led, buck ratio, the lower the efficiency the greater the wear and tear on the chip’s power consumption.

 

Adjust the forward current cannot be precise dimming. Because the forward current and light output is not completely proportional relationship between the different high intensity uv leds have different forward current and light output curve. So adjust the forward current is difficult to achieve precise light output control.

 

The led high bay is a diode, it can achieve fast switching. The switching speed can be up to the microsecond above. Is unmatched by any light-emitting devices. Therefore, as long as the power source into a pulsed constant current source, the method of changing the pulse width can change its brightness. This method is called pulse width modulation (PWM) dimming method. If the pulse cycle tpwm, pulse width of the ton, the D (or called porosity) ton / tpwm. Work to change the pulse of constant current source can change the brightness of the high intensity uv led.

Problems suffer for high lumen led flashlights used in daily life

 

Problems suffer for high lumen led flashlights used in daily life

 

In the specific implementation, however, adjust the forward current dimming may produce a more serious problem.

 

We know that the c is usually driven DC-DC constant current drive power, and such constant current drive source is usually divided into two kinds of step-up or step-down (of course, the buck, but because of low efficiency, The prices are not commonly used). LED forward voltage is determined by its forward current. We can see from the volt-ampere characteristic of the LED forward current changes will cause the corresponding changes of the forward voltage, or more precisely, the decrease of the forward current can also cause the forward voltage decreases. Therefore, to reduce the current, led high bay light forward voltage will follow reduced. This will change the relationship between supply voltage and load voltage.

 

For example, an input of 24V LED lamps, 8 1W high power LED series. For a boost type constant current source must work at the buck does not work, the last high lumen led flashlights will flicker. In fact, as long as the boost type constant current source, adjust the forward current dimming transferred to the low brightness almost certainly will produce flicker. Time of the LED load voltage must be lower than the supply voltage. Many people do not understand one of the problems, but also the total going to the dimming circuit to find the problem, it is futile.

 

Step-down constant current source of as if originally the supply voltage is higher than the load voltage when the brightness is to low-key, the load voltage is reduced, they still need to step-down constant current source.

DC power supplied led dimming technology

 

DC power supplied led dimming technology

 

Adjust the forward current to adjust the brightness to change the brightness of the LED is very easy to achieve. The first thought is to change the drive current, because the brightness of the led dimming technology is almost directly proportional to its drive current.

 

1.1 to adjust the forward current

Current sense resistor to adjust the LED current to the most simple way is to change and LED load series, almost all DC-DC constant current chip has a detection current interface is detected by the voltage and chip internal reference voltage to control current constant. But the sense resistor value is usually very small, only a few tenths of Europe, if you want installed in the wall a few tenths of Europe’s potentiometer to adjust the current is unlikely to lead resistance there will be a few tenths of Europe. Some chips provide a control voltage interface, changing the input control voltage can change its output constant current value.

 

Forward current of 1.2 tone makes chromatography offset

However, to adjust the forward current to adjust the brightness will have a problem, that is, adjust brightness while also change the spectrum and color temperature. Because the white led high bay excitation with blue light LED yellow phosphor, yellow phosphor thickness without a proportionate thinning, when the forward current is reduced, the blue led high bay brightness increase, making it the dominant wavelength of the spectrum increased.

 

Of course, these problems in the general led dimming technology may not be a big problem. RGB LED system, however, will cause the color offset, the human eye color deviation is very sensitive, and therefore cannot be allowed.

The price of high output led bulb is quite close to energy-saving lamps

 

The price of high output led bulb is quite close to energy-saving lamps

 

LED chip Diving high output led bulb prices approaching the energy-saving lamps

“Two years ago, 1-watt LED chip price is about $ 3, but is now down to less than $ 1 cheaper, Taiwan and the mainland-produced chips, or even three yuan a. Foshan Lighting Association Wu Yulin told the author. May Xu Rui Optoelectronics put into operation the LED chip, the official told the author, “probably in nearly a year’s time, chip prices fell more than 6 to more than 2 yuan.

 

It is understood that the chips accounted for at least 1/3 of the cost of high output led bulb, chip price cuts directly drive the LED price decline. In recent years, chip prices fell about 20% of the annual rate, the price of led high bay from two years ago is generally 7-10 times the energy-saving lamp, dropped to 3-4 recent times. At present, the price of energy-saving lamps has been stable at $ 6-10, and LED lamps from 50-300 down to 30-100 yuan.

 

I visited yesterday the Chancheng of Wal-Mart and Weiguo Lu many lighting stores learned that generally 10% -30% increase in sales in the first half of the LED lights. “Nearly a year, the price of LED products generally decreased by 30%, mid-range price of high output led bulb is probably between 100-300 yuan, nearly two months of business to maintain 10% growth.” To operate in the Great Patriotic Road the glare of Green lighting Co., Ltd. business on behalf of the European Jingyang said.

History of the LED street lighting: as fast as a train

 

History of the LED street lighting: as fast as a train

 

The first stage, LED lamps, utility model stage.

On the basis of the previous stage, the market for LED street lighting products has been recognized and accepted. Other features of environmental protection, small size, high reliability of the LED lamps are increasingly prominent. Thus developed a series of products will be completely different from the traditional light source applications become very popular. The lighting industry will be a more open space for development. Light source is no longer only play a role in lighting, it’s changing bit by bit in making more appropriate for people working and living. The fight by the various manufacturers is to design application advantage.

 

The second stage, LED street lighting, smart control stage.

With the development of things such as new technology, the LED as the semiconductor industry, will also catch this tour high-speed train to play out its high controllability. From home to office buildings, from the road into the tunnel from the car to walk from the auxiliary lighting to the main lighting with LED street lighting intelligent control systems will give mankind a higher level of service. Led high bay lighting industry will also be doing product design product, to providing total solutions to the course.

 

The third stage, the LED lamps to replace the acceptance phase.

This phase is mainly luminous efficiency (energy consumption), and long life LED lamps in the early stages of development. The customer has an acceptable process, the first transition and on the habits and appearance. The consistent use of traditional light sources, LED street lighting reflects the energy saving, longevity and other features make the market easier to accept the relatively high prices.