As a new light source, the near LED power supply and drive circuit are different from the electronic ballast of the fluorescent lamp. The main function of the LED drive circuit is to convert the AC voltage into a DC voltage and simultaneously match the voltage and current of the LED . As the silicon integrated circuit power supply voltage drops linearly, the LED operating voltage is more and more in the optimal range of the power supply output voltage. Most of the low-voltage IC power supply technologies are also suitable for powering LEDs, especially high-power LEDs. . In addition, the LED power supply should also be able to take advantage of the economies of scale brought about by the gradual increase in the output of low-voltage IC power supplies.
First, the main technical overview of LED power supply and drive circuit
1) Voltage conversion technology
Power supply is an important part of the reliability and adaptability of LED light sources. At present, the mains electricity in China is 220V AC, and the LED light source is a semiconductor light source, which is usually powered by DC low voltage. This requires AC-DC conversion circuit in or outside of these lamps to adapt to the characteristics of LED current drive. At present, the power supply selection methods include switching power supply, high-frequency power supply, and capacitor rectification and rectification power supply. Various options are selected according to different requirements such as current stability, transient overshoot, and safety and reliability.
2) Life and cost of power supply and drive circuit
In terms of LED life, although the life of a single LED itself is as long as 100,000 hours, its application must be matched with a power conversion circuit. Therefore, the overall life of an LED lighting device must be considered from the optoelectronic integration application. However, for lighting LEDs, in order to meet the matching requirements, the life of the power supply and the drive circuit must exceed 100,000 hours, making it no longer a bottleneck factor for the LED lighting system. Considering long life and not increasing too much cost, the life and cost of power supply and drive circuit should not exceed one third of the total cost of lighting system. In the early stage of LED lighting products development, power supply must be balanced. The relationship between the life of the drive circuit and the cost.
3) Programmable technology for drivers
A significant feature of LEDs as light sources is their ability to maintain lumens efficiency even at low drive currents, while also for RGB polymorphs.
In the case of mixing light to form white light, by developing a digital RGB hybrid control system for LEDs, the user can adjust the brightness, color and color of the LEDs in a wide range, giving a new visual enjoyment. . In the urban landscape lighting application, the LED light source can be changed according to different modes under the control of the microprocessor, forming a dynamic effect of the night, which will reflect the uniqueness of the LED relative to other light sources. Competitive Advantage.
4) Efficiency of power supply and drive circuit
The LED power supply and the driving circuit must have a certain forward current output close to the constant current required for the LED, and have a high conversion efficiency. The electro-optical conversion efficiency is an important factor of the LED illumination, otherwise the LED will be lost. The advantage of energy saving, the current commercial switching power supply has an efficiency of about 80%. As a power source for LED lighting, its conversion efficiency still needs to be further improved.
Second, the trend of technology development
1) Develop a series of constant voltage constant current control electronic circuits for the characteristics of LEDs, and use integrated circuit technology to control the input current of each LED to the optimal current value, so that the LED can obtain a stable current and produce the highest output luminous flux. The LED driver circuit preferably controls the magnitude of the LED current when factors such as input voltage and ambient temperature fluctuate.
2) The LED driver circuit has an intelligent control function, so that the load current of the LED can be controlled at a pre-designed level under the influence of various factors. When the load current changes due to various factors, the primary control IC can control the switch to return the load current to the initial design value.
3) In the design of control circuit circuit, it is necessary to develop into three aspects: centralized control, standard modularization and system scalability.
4) Under the current LED light effect and limited luminous flux, fully exploit the characteristics of LED color diversity, and develop control circuits for color-changing LED lighting .
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