Interpretation of the development trend of LED driver power technology

As a new light source, LED power supply and drive circuit are different from the electronic ballast of fluorescent lamps. The main function of LED drive circuit is to convert AC voltage into DC voltage and match the voltage and current of LED at the same time. With the straight-line decline of silicon integrated circuit power supply voltage, LED operating voltage is increasingly in the optimal range of power supply output voltage. Most technologies for powering low-voltage ICs are also suitable for powering LEDs, especially high-power LEDs. In addition, LED power supply should also be able to take advantage of the economies of scale brought by the gradual increase in the output of low-voltage IC power supplies.

1. Overview of main technologies of LED power supply and drive circuit

1) Voltage conversion technology

The power supply is an important component that affects the reliability and adaptability of LED light sources and must be considered as a priority. At present, my country's mains electricity is 220V AC, while LED light sources are semiconductor light sources, usually powered by low-voltage DC. This requires the installation of AC-DC conversion circuits in or outside these lamps to adapt to the characteristics of LED current drive. At present, there are many ways to choose power supply, including switching power supply, high-frequency power supply, capacitor step-down and rectifier power supply, etc. Different choices are made according to different requirements for current stability, transient overshoot, 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 up to 100,000 hours, it must be used with a power conversion circuit, so the overall life of LED lighting fixtures must be considered from the perspective of optoelectronic integration applications. However, for lighting LEDs, in order to meet matching requirements, the life of the power supply and drive circuit must exceed 100,000 hours, so that it no longer becomes a bottleneck factor in the LED lighting system. While considering long life, the cost should not be increased too much. The life and cost of the power supply and drive circuit should not usually exceed one-third of the total cost of the lighting system. In the early stages of the development of LED lighting products, the relationship between the life and cost of the power supply and drive circuit must be balanced.

3) Programmable technology of driver

A notable feature of LED as a light source is that it can maintain its lumen efficiency under low driving current conditions. At the same time, for RGB polycrystalline light mixing to form white light, by developing a digital RGB mixing control system for LED, users can adjust the brightness, color and hue of LEDs in a wide range, giving people a new visual enjoyment. In the application of urban landscape lighting, LED light sources can be changed in different modes under the control of microprocessors to form a variety of dynamic effects at night. In this regard, it will reflect the unique competitive advantage of LED over other light sources.

4) Efficiency of power supply and drive circuit

LED power supply and drive circuit must have a certain forward current output close to the constant current required by LED, and have a high conversion efficiency. The electro-optical conversion efficiency is an important factor in LED lighting, otherwise the energy-saving advantage of LED will be lost. The efficiency of the current commercial switching power supply is about 80%. As a power supply for LED lighting, its conversion efficiency still needs to be further improved.

2. Technology Development Trends

1) Develop a series of constant voltage and constant current control electronic circuits based on the characteristics of LEDs, and use integrated circuit technology to control the input current of each LED at the optimal current value, so that the LED can obtain a stable current and produce the highest output luminous flux. The LED drive circuit is best able to control the size of the LED current when factors such as input voltage and ambient temperature change.

2) The LED drive circuit has an intelligent control function, which enables the LED load current to 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 terms of control circuit design, it is necessary to develop in three aspects: centralized control, standard modularization, and system scalability.

4) Given the current limited LED lighting efficiency and luminous flux, we should give full play to the color diversity of LEDs and develop control circuits for color-changing LED lighting.