LED drive power is one of the core components of LED lighting products. Its performance has an extremely important impact on the overall quality of lighting products: the efficiency of driving power supply is not high, the energy conversion ratio is low, which not only affects the lighting quality of lighting products, but also Bringing a large heat dissipation problem; driving failure is an important factor affecting the life of LED lighting products. Statistical analysis of 5400 ç› outdoor LED street lamp failure data in Elwood City, USA, 59% failure of LED street lamps and driving power supply and its control devices Related to failure. LED driver failure is related to many factors. Electromagnetic interference is an important aspect. Especially with the development of drive technology, the electronic integration of drive power is getting higher and higher, including not only the drive circuit, but also the LED electronic control or dimming circuit. . Therefore, the testing and evaluation of its electromagnetic compatibility characteristics (including electromagnetic interference and anti-interference) is very important, and it is an important factor to consider driving failure. 
In recent years, dimming technology has been gradually applied in the field of LED lighting, especially in the field of commercial lighting. Dimmer Compatibility and Flicker performance have attracted the attention of many international standards organizations, such as the US Energy Star and the International Energy Agency's 4E plan, all of which propose dimming compatibility and strobe. Testing requirements. Therefore, the test and evaluation of the LED driver should be based on its own functional characteristics, and through comprehensive testing methods, it should be considered comprehensively.
LED drive power related standards
The standards for LED drive power include the requirements for LED drive electrical performance, EMC electromagnetic compatibility, and testing. In April 2013, ENERGY STAR released the final draft of the ENERGY STAR® Program Requirements Product Specification for Lamps (Lamps FD), which included the testing of the ringing wave in the transient protection characteristics. The test standard is ANSI/ IEEE C62.41.2. At the same time, for dimmable LEDs, it is also required to measure the maximum value of the flicker indicator. The International Energy Agency (IEA) has previously proposed that the Flicker Index should not be greater than 0.3% for full-power street lighting. From the perspective of the standards and the development trend of international standards, LED drivers not only need to measure the basic electrical properties, EMC and other characteristics, but also need to investigate the transient protection characteristics and scintillation index and other characteristic parameters according to their applications.
System test plan for LED drive power
2.1 Electrical performance test
The electrical performance is the basic characteristic of LED driving. The performance of this performance is directly related to the light quality and energy efficiency conversion of LED. There are many parameters to be considered, including steady flow (voltage) range, power factor, startup time, and output overvoltage ( Flow) protection value, input surge current, and output current (voltage) ripple. Such a large number of electrical performance indicators, generally need to use a variety of testing equipment combined measurement, the operation is very cumbersome. Figure 1 shows a typical LED power performance analyzer (LT-101). Figure 2 shows the measurement principle of the LT-101 LED driver. The LT-101 can simultaneously test the input and output characteristics of the LED driver. All measurement content is met to meet the standard requirements, and the LT-101 also features output ripple measurement and harmonic analysis.
Figure 1 Typical LED Power Performance Analyzer
Figure 2 Test schematic
2.2 Electromagnetic compatibility testing
The EMC (Electromagnetic Compatibility) of LED driving power sources includes electromagnetic interference (EMI) and electromagnetic sensitivity (EMS). EMI (Electromagnetic Interference) requires that the electromagnetic interference generated by the LED drive power system during the normal operation of the environment and other things (including equipment, systems, people, animals and plants) should not exceed certain limits. EMS (Electromagnetic Susceptibility) is electromagnetic sensitivity (immunity resistance). This characteristic requires the LED driving power system itself to have stable running performance under electromagnetic disturbance, such as the ability to resist lightning, static electricity, ringing waves and the like. For different EMC characteristics, the standard test requirements are different, and you must select your own professional test plan for testing. The following is a description of the EMS performance tests that are important for LED driver power supplies and are the most prone to failure.
2.3 Surge impact detection
Natural lightning strikes, power system switching, equipment grounding grids or short circuits between grounding systems can cause surges in the LED drive in this environment, which can lead to equipment failure and damage. Therefore, the standard GB/T 17626.5/IEC61000-4-5 has clearly defined the anti-surge impact performance evaluation of electrical equipment. The lightning surge test system for LED drive power is shown in Figure 3. The main equipment is a fully automatic multi-function lightning surge generator. It superimposes a surge spike on the 220V mains, with a maximum value of 10kV and a peak rise time. And the duration is 1.2 μs / 50 μs.
2.4 Electrostatic discharge detection
There are many semiconductor devices in the LED driving power circuit, which may encounter electrostatic discharge during manufacturing, assembly, transportation, storage and use, resulting in malfunction and failure of the LED driving power supply. Electrostatic discharge testing of LED driver power electronics can be performed in accordance with US National Standards ANSI/ESD STM5.1, ANSI/ESD STM5.2, US Military Standard MIL-STD-883, and International Electrotechnical Association Standards JESD22-A114D, JESD22-A115 -A, etc. Figure 4 is an ESD-1000 LED electrostatic analysis test system designed for LED electrostatic testing. The machine mode (MM) and human body mode (HBM) electrostatic discharge test can be realized according to the standard requirements, and the discharge voltage can be up to 30kV. In addition, for the electrostatic discharge immunity of the overall LED drive power system, the test shall be carried out in accordance with GB/T 17626.2/IEC61000-4-2. Contact discharge is the first test solution, and air discharge can be used at locations where contact discharge is not possible. Indirect discharge shall be tested according to the content specification of Section 7 of GB/T17626.2.
2.5 ringing wave detection
The ringing wave detection is mainly for examining the ability to drive interference against the switching of the power line and the control line switch of the electronic and electrical equipment in the power grid, and the ringing wave waveform is as shown in FIG. 5. This feature has been included in the product certification requirements by ENERGY STAR and indicates that the test is performed in accordance with ANSI/IEEE C62.41.2. In addition, the standard IEC61000-4-12 and GB/T17626.12 also regulate this. Figure 6 shows a typical ringing wave generator (EMS6100-12C) with an oscillation frequency of 100 Hz, a test voltage peak of up to 6 kV, and a maximum of 60 transients per minute, which is well suited to meet the test requirements of each relevant standard.
Figure 5 ringing wave waveform
Figure 6 Ringing Wave Generator
LED drive power related dimming compatibility and stroboscopic characteristic detection
Dimming technology has been gradually applied to various types of LED lighting products, and the process of intelligent lighting has been opened, but the dimming compatibility and stroboscopic characteristics brought about by this have also attracted much attention. The LED can be dimmed by an integrated dimming circuit inside the driving power supply or by an external dimming controller, but both of them often cause LED ripple output ripple due to incompatibility of the driving circuit, and the LED light source strobes. In theory, the stroboscopic characteristics can be measured by the output ripple characteristics (measured by the LT-101), but more of them reflect the LED light output characteristics. Therefore, the measurement of the light output variation characteristics through the LED will More objective.
Strobe can cause visual fatigue, vertigo, migraine, etc., and in the field of road lighting, strobo can also cause the driver to have the illusion and cause traffic accidents, so it is getting more and more attention from relevant international standards organizations. Both the US Energy Star and the International Energy Agency (4E Program) have performance requirements. The former specifies in its Lamps FD that the lighting fixtures need to measure the maximum value of the scintillation indicator. The latter stipulates in the performance specifications of its SSL street lighting fixtures that the flashing index of the luminaire is not more than 0.3% at full power. Figure 7 shows a typical LED stroboscopic test system. The core detection device is the FSH-2000 high-speed flash analyzer (see Figure 8). The sampling width of the device is adjustable from 1-12s, and its sampling frequency is up to 20kHz. Fully meet the requirements of ENERGY STAR's latest test standards.
Figure 7 Typical LED strobe test system
Figure 8 Test equipment
The evaluation parameters of the stroboscopic characteristics of the LED lamp include a Percent Flicker and a Flicker Index. Figure 9 is from the Lighting Handbook of the North American Lighting Association (IESNA). A and B are the maximum and minimum values ​​of the luminous flux fluctuation curve in a cycle. The average optical output is bounded, and the test waveform is divided into Area1 and Area2, and the percentage of flicker and flicker. The index can be given by the formula in the figure. Figure 10 is a waveform diagram of the flicker measurement of an LED lamp by the FSH-2000 analyzer. The built-in software calculates the percentage of flicker (37.555%) and flicker index (0.1004) of the LED lamp according to the waveform.
Figure 9 IESNA flicker test indicator
Figure 10 A LED flashing waveform measured map
summary
The driving power of LED can be said to be the core component of LED, and its performance quality has a great influence on the energy efficiency, reliability and lighting quality of LED. With the development of LED driver technology, some new performance parameters, such as stroboscopic indicators, have attracted a lot of attention, related standards have become more and more perfect, and the corresponding test equipment has also matured. According to the characteristics of the products, LED driver manufacturers should select the corresponding testing scheme to comprehensively characterize and evaluate the characteristics of the driving power supply according to the development requirements of domestic and international standards. This not only improves the overall quality of LED lighting products, but also helps to further standardize LED lighting. Product development.
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