Author Zhang Yaokun Retired Engineer
Shanghai Aoxing Lighting Appliance Co., Ltd.
[ Abstract] The principle of commercial power adaptive control researched by the author, created the proprietary (patent) technology of 220V commercial LED lighting constant current control circuit. The circuit is very classic, no need to add Vcc power supply, no transformer, inductor coil, etc., directly use 220V mains and immediately drive LED, with manual dimming function, it can also be easily dimmed automatically.
Seeking new changes and promoting independent research and development <br> The author entered the field of large-scale application of LEDs many years ago, and witnessed the high quality of LED Lighting devices from high quality to gradually improving quality, from low luminous intensity products to high brightness and ultra high brightness. development of. With the emergence of relatively large power and high-efficiency devices, the price of the product has also dropped significantly; it is possible to expand from the application range of display and signal lamps to the broader market of general lighting applications, and also to work in LED applications. Provides the basis for the ability to perform.
When faced with the large-scale application of LED traffic light products, there was a concept of thinking: although the LEDs used have many limitations and even deficiencies, they cannot do nothing but do their part. As the LED application industry has to consider, how to make full use of its potential at the level of existing devices, that is, need to understand the LED characteristics, use LEDs.
LED is essentially a current device that produces light by current; it is equivalent to a Zener in electrical characteristics. When the current flowing changes, the voltage change at both ends is small. However, if the applied voltage is slightly larger than the regulated value of the LED, the current flowing through it will change greatly, so the LED must be powered by the current source and require constant current. It is not the best policy to attempt to regulate the power supply and then use the resistor current limiting method. Because the LED generates heat and aging during operation, the voltage drop changes. Finally, the voltage difference changes to cause the operating current to mutate.
When people question the LED performance or failure rate is not satisfactory, the inherent congenital deficiency of LED should be objective, because the development and progress of anything needs a process, not to mention the LED has an extraordinary prospect. You can first check and test the working status and production process of the device.
It must be understood that LEDs are a delicate device, so applications always want to get as much luminous flux as possible from LEDs to reduce costs. The operating current tends to be close to the upper limit, but even a short-term accidental overload due to power surges, induced currents, etc. will inevitably cause damage to the device. Therefore, it is necessary to ensure the necessary current margin or strict and reliable protection measures.
The silver paste conductive structure and epoxy package inside the LED inevitably have stress damage in the case of thermal expansion and contraction, and the light decay cannot be prevented under high current and high temperature.
Temperature and heat dissipation conditions are sometimes more likely to be fatal killers, so the temperature and time of soldering during production must be controlled beyond the standard, and subsequent cooling is also important. Because it is convenient to dissipate heat from the leads, the thermal resistance is made small, and the heat is also easily transferred from the pins. When the pins are processed short, the heat transfer is even worse; sometimes the increase in device failure rate is often caused by negligence in the soldering process. of.
Although there are so many problems to solve, it is not necessary to be so discouraged. This is a good time for LED application workers to play a role. It can be seen that so many companies in the world have developed LED driver chips in the form of a form, which not only reflects the wisdom and enthusiasm of the elites in the industry, but also shows the promotion of booming business opportunities. Originally, lighting products have a very large proportion directly used on the mains grid, so green energy-saving mains LED lighting will have huge market demand potential.
To promote the application of LED in the lighting of the city, it is necessary to find out its particularity, in order to achieve the effect of getting twice the result with half the effort. Different from the DC low-voltage conditions of the mature applications, the mains voltage is relatively high, in addition to personal safety, there is the possibility of breakdown and fire. Therefore, the driver needs to be different; in order to reduce the power consumption of the driver and improve the lighting efficiency, the LED component should be arranged to work at a high voltage and a small current, that is, to use the LED in series. This is similar to the transmission of large power grid transmission lines with ultra-high voltage transmission. Therefore, the use of many low-power LEDs in series is more energy efficient than using a small number of power LEDs (the power LEDs are actually equivalent to many low-power LED chips connected in parallel). And from the product indicators, it can be seen that the three 1W LEDs add up a lot more than a 3W light effect. When multiple devices are dispersed, it is more conducive to heat dissipation and cooling, which also improves light efficiency. This is the most energy-saving design concept.
Independent innovation stems from the experience and accumulation of technology
To develop the mains LED lighting products, the concept should be broadened first. There is no way to imitate the past products. If you want to replace the incandescent lamps, you want to put the LEDs and driving circuits into the bulbs. If you want to make fluorescent lamps, you will never forget the fine. Long pipe.
If you simulate too much, you can't make it true. If you stick to the old form, you won't be able to create a new situation. There is nothing wrong with the standard of the mouth of the incandescent lamp, but it is also advisable to design the lampshade together. With a little engineering plastic, the LEDs and the drive circuit can be dispersed very well to create a natural ventilation and heat dissipation environment. LED illuminators with a plastic shade can not add much cost, but can play a decisive role in LED safety, stable use and satisfaction with light distribution.
As for the fluorescent lamp, which is mainly the ceiling lighting fixture, why bother to do the growth of the strip shape, you can completely make the required "area lighting". At that time, problems such as heat dissipation and uniformity of illumination will be solved.
As a commercial power and its special performance in communication, the author studied the precision communication of a feedforward technology for more than 30 years ago because it did not meet the performance of an AC voltage regulator controlled by a tungsten diode sensor plus a reactor. The voltage circuit, although there is no opportunity to form a product, has some doubts about the city. A few years ago, I dissipated my thoughts and studied the principle of commercial constant-current constant-current driving LEDs, creating a unique proprietary (patented) technology for LED lighting control circuits using utility power. See the topic for details.
In short, the characteristics of the mains are used to directly drive the LED lighting fixture so that it can adapt to the fluctuation of the grid voltage and always maintain the set constant current state.
Recently, NXP has seen the allegedly the world's first integrated dimmable mains LED driver, the SSL2101. After comparison, it was found that the commercial power adaptive control circuit created was much simpler than the SSL2101. A total of only a dozen low-power general-purpose diodes and bipolar transistors are integrated into the chip. No need for special Vcc power supply, no transformer, inductor coil, etc., directly use 220V mains and can drive LED immediately. In addition to manual dimming function, it can be easily dimmed automatically.
Has been made with 121 LEDs at night to automatically reduce the brightness of the light, in line with European energy-saving standards of traffic lights, also made according to the ambient light brightness, off during the day, automatically lit at night, with 16 LED lighting light. In the working range of 180V ~ 250V, the constant current stability of about 1% is achieved, and the test remains unchanged after two years. It shows that in the commercial power application, the mains adaptive LED Constant Current Driver can be used in both the number of LEDs used and the way of automatic dimming. It has unique performance and cost than SSL2101.
The mains adaptive LED constant current driver chip pin is shown in Figure 1. The typical application block diagram is shown in Figure 2 and Figure 3.
The driver chip in the figure has not been put into production, so the original model is replaced by a discrete device module. But it is obvious that those common low-power crystal diodes and transistors can be easily integrated in IC manufacturers. In Figure 2, RV1 is used to adjust the constant current value, that is, the brightness of the light. RV2 is used to adjust the threshold of ambient light when the light is turned on and off. RV1 in Figure 3 is used to adjust the operating current value of the traffic signal. In the figure, RB is the photosensitive resistor that automatically adjusts after the light is applied. The peripheral circuit uses less than ten low-power resistors and four low-voltage capacitors. Figure 7 and Figure 8 show the outline of the sample that has been produced. Figure 9
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