In the LED industry, it is well known that powering a LED with a constant current source is the best power supply solution. In recent years, a variety of constant current drives have emerged. Many manufacturers started from the definition of "constant current" and grafted the technology and experience of producing constant voltage power for many years to the constant current driver to produce a constant current driver with high constant current accuracy and good performance indicators.
The stability of the output current of the constant current driver is mainly affected by factors such as power supply voltage fluctuation, LED load change, and ambient temperature change. The constant current driver uses the current negative feedback principle of LED current sampling to eliminate the influence of various interference factors on the constant current value. It is called a high precision constant current driver. We call it an unconditional constant current driver.
Is the high-precision unconditional constant current driver the best driver for LEDs? Actual use indicates that the answer is no. Because its performance does not fully meet the requirements of LED. In the condition of power supply voltage fluctuation and LED load change, in order to stabilize the LED operation, constant current is necessary, but when the ambient temperature changes, it is not correct to maintain constant current.
analyse as below:
LEDs are semiconductor components that are sensitive to temperature and have certain temperature characteristics. Figure 1 is the curve of the LED operating current and ambient temperature provided by the LED manufacturer (shown by the solid line). It indicates that in order to make the LED junction temperature not exceed the maximum allowable value (about 100 ° C), the operating current of the LED should decrease with the increase of the ambient temperature. In response to the actual requirements of LEDs, we have tailored an LED dedicated constant current driver for LEDs - "Intelligent Constant Current Driver". It can maintain constant current under the conditions of power supply voltage fluctuation and LED load change. When the ambient temperature is raised, the constant current value is automatically decreased (about -0.3%/°C) close to the required value of the LED (indicated by the dotted line). In order to distinguish from unconditional constant current, we call this new constant current method a conditional constant current.
The use of conditional constant current can prevent the LED from being overheated in a high temperature environment, avoiding the reduction of light efficiency and speeding up the light, and achieving the purpose of prolonging the service life of the LED.
The output characteristics of the unconditional constant current (shown by the horizontal dashed line) and the output characteristics of the conditional constant current (shown by dotted lines) are also shown in FIG. They are compared: the unconditional constant current overload starting temperature t1 is lower than the conditional constant current overload starting temperature t2; the unconditional constant current of the LED overload is much higher than the conditional constant current.
Unconditional constant current, LED is a working current in winter and summer, and conditional constant current in winter and summer LED working current is different, summer working current will automatically decrease. The high temperature of the working environment in summer is unfavorable for LED heat dissipation, and it is very reasonable to reduce the working current appropriately.
Some people may ask: Reduce the LED operating current will reduce the brightness of the LED? The answer is: 1. When the temperature is high, the working current is appropriately reduced to prevent the LED from being seriously overloaded, and the service life is greatly extended. Even if the brightness is slightly lowered, the trade-offs are worthwhile. 2. From the relationship between the luminous flux and the junction temperature of the LED output of Figure 2, it can be seen that when the operating current decreases and the junction temperature decreases, the luminous efficiency of the LED increases, and the luminous flux also increases (about -0.8%/°C), which gives A certain amount of compensation is given due to a decrease in luminous flux caused by a drop in operating current. In fact, the brightness of the LED is not significantly reduced, and the impact on the normal operation of the LED lamp is small. It is almost invisible to the naked eye.
According to the innovative design concept of “conditional constant currentâ€, we have produced five series of products such as 0.35A, 0.5A, 0.7A, 0.9A and 1.5A.
Their common feature is: "three high."
First, high work reliability
The constant current driver has many protection functions such as short circuit, open circuit, open circuit and anti-shock, reverse connection, anti-overheating, etc. (the first two protection drivers, the last three protection LEDs) ensure the constant current driver and LED lamp in various Safe use under working conditions. In particular, we have broken through the problem of “opening and then connecting with anti-shock†protection and applied for national patents. Short circuit, open circuit protection power consumption <1W. Working temperature rise <20 °C. The service life is 25,000 hours, more than 5 years.
Second, efficient energy saving
The constant conversion efficiency of the constant current driver is 93%; the power factor is >0.9.
Third, high cost performance
Good performance and low cost.
The intelligent constant current driver has an output power range of 25W-120W, which is mainly used with high-power LED street lamps, high-power LED floodlights, and high-power LED floodlights.
Solar LED land lamp uses sunlight as the energy source, charges during the day and uses at night, does not need complex and expensive pipeline laying, can arbitrarily adjust the layout of lamps and lanterns, safe and energy-saving, pollution-free, stable and reliable without manual operation, saving electricity and maintenance. Solar LED street lamp is mainly composed of solar cell module (including bracket), LED lamp holder, control box (with controller, battery) and lamp pole.
Solar Led Street Light,Street Light Lamp,Solar Powered Street Lights,Solar Powered Led Street Lights
Yangzhou Heli Photoelectric Co., Ltd. , http://www.heli-eee.com