Analysis of the hottest LED lighting test technolo

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Analysis of LED lighting test technology

in recent years, as a new energy-saving light source, LED has won high investment enthusiasm and great attention in the world and China, and has penetrated from outdoor to indoor lighting application market. Tens of thousands of LED lighting enterprises, large and small, have also emerged in China. The main reason for LED lighting to shine is that it advocates 4. Conference cost: 2000 yuan/person, energy saving, environmental protection, long life, easy to control, maintenance free and other characteristics

however, it is ironic that we often hear that led lighting fixtures are not "long-lived" because the service life of LED driving power supply itself directly affects the service life, which greatly increases the maintenance/use cost; Or the efficiency of the driving power supply is not high, resulting in the energy efficiency conversion ratio of LED lighting is not as high as expected, or the output current ripple is not well controlled, which affects the luminous quality, which greatly reduces the green energy-saving advantage of LED lighting, and even affects the market popularity

therefore, the driving power supply is also an important part of the improvement and maturity of the LED industry chain. However, the current situation is that the design and quality limitations of LED driving power supply have increasingly become the "hind legs" of the development of LED industry. Therefore, power module manufacturers and lamp manufacturers are paying more and more attention to the use of advanced testing and measurement technologies and schemes. In view of this situation, Tektronix is unique. It goes deep into customers, understands the actual needs of the site, and formulates various solution combinations for LED vertical applications, aiming to help more Chinese LED lighting manufacturers, drive power suppliers and relevant quality inspection/certification institutions obtain more accurate test results, ensure the quality of LED drive power, and promote the healthy and prosperous development of China's LED lighting industry

the reliability and energy efficiency of LED driving power supply are the key to the test

then, what characteristics or requirements should a truly high-quality LED driving power supply have? Tech summarizes the following main aspects:

1 High reliability and service life: the service life of the driving power supply should match the service life of the LED, especially for the driving power supply such as the LED street lamp, because it is installed at high altitude, it is inconvenient to maintain, and the maintenance cost is also large

2. High efficiency: This is particularly important for the structure where the power supply is installed in the LED lamp. Because the luminous efficiency of LED decreases with the increase of temperature, but its performance depends on the operation of computer servo system, so the heat dissipation of LED is very important. The efficiency of the power supply is high, its power consumption is small, and the calorific value in the lamp is small, which reduces the temperature rise of the lamp and is beneficial to delaying the light failure of the LED

3. High power factor: with the continuous improvement of social requirements for power supply quality, people pay more and more attention to the power quality and harmonic problems brought by electric equipment. For example, the European Union has issued standards that stipulate that power supply equipment with power greater than 25W must have power factor correction circuit. While many other countries may have certain index requirements on power factor for 30 ~ 40W LED driving power supply in the near future

4. Constant current drive: there are two kinds of current: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. The combination of this method is flexible, and the failure of one LED will not affect the work of other LEDs, but the cost will be slightly higher. The other is direct constant current power supply, LED series or parallel operation. Its advantage is that the cost is a little low, but the flexibility is poor. It also needs to solve the problem that the failure of one LED does not affect the operation of other LEDs

5. Appropriate output ripple: the output ripple will affect the light output effect of LED. However, reducing ripple requires the use of higher quality and capacity capacitors. In order to improve the overall service life of the power supply, designers tend to adopt the scheme without capacitance. Engineers must determine a compromise on the output ripple index

6. Surge protection: the anti surge ability of LED is relatively poor, especially the anti reverse voltage ability. Some LED lights are installed outdoors. Due to the start and fall of electrical load and the induction of lightning stroke, various surges will invade the secondary electrical system, and some surges will cause led damage. Therefore, the LED driving power supply should have the ability to suppress the invasion of surge and protect the LED from damage

7. Protection function: in addition to the conventional protection function of the power supply, it is best to add LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high

8. Protection: for the external installation structure of lamps, the power structure should be waterproof and moisture-proof, and the shell should be sun resistant

9. To comply with safety regulations and electromagnetic compatibility: ε T is elongation at break or elongation at yield; Please

in order to meet the design standard of high-quality driving power supply, comprehensive testing, measurement and analysis are required. As shown in Figure 1, LED lighting test mainly includes five parts: power quality, harmonic, power switching device measurement, modulation analysis and driving output parameter test

Figure 1: Tektronix provides a variety of test solution combinations for LED lighting applications for customers to choose

comprehensive and rapid analysis of power quality, harmonics and power devices

there are many ways to measure the input power, power factor and harmonic of the driving power supply. These power quality measurements can be easily achieved by using tektix oscilloscope products with power source analysis function. Using one channel to measure the input voltage and one channel to measure the input current, together with the PWR power analysis software built into the oscilloscope, all power quality related parameters can be directly displayed on the screen

drive power efficiency and electricity do you know what characteristics of fatigue testing machine equipment and which parts need maintenance? The switching loss inside the source is directly related. Reducing the loss of power devices is not only the requirement of improving power efficiency, but also the key factor to improve the thermal stability and reliability of the system. However, it is difficult to measure the switching loss of power devices. Because the voltage amplitude of the device in the on and off working states varies greatly, ordinary oscilloscope products cannot accurately measure the small voltage in the on state under such a large dynamic range, and the on loss cannot be measured

for power devices with high-speed switching, the power can only be calculated by multiplying the voltage and current to obtain the transient power. At this time, the voltage and current must be the waveform at the same time, otherwise the error is huge. However, the principle and structure of voltage probe and current probe are different, and the time delay of high-speed switching signal is also different. If this deviation cannot be corrected accurately, the measurement result of the oscilloscope is not credible. Tektronix's oscilloscope power measurement scheme not only has a comprehensive switching loss test function, but also has a powerful probe calibration function to completely eliminate the time delay error. The unique waveform search function makes it easier to find the time when the maximum loss occurs when the power supply or load changes

specific to the model, dpo/mso4000b and dpo/mso3000 Series Oscilloscopes are good choices for R & D process tests that require high requirements; For the design optimization and parameter test application of factories and production processes, dpo/mso2000 series can fully meet the requirements and further reduce the cost (Tektronix has also recently launched DPO popularization preferential activities. For details, please log in:). These oscilloscopes have a long storage length per channel, which can capture the whole cycle of driving power measurement with high sampling rate. Waveform navigation is convenient for power system troubleshooting, and advanced mathematical calculation function. Users can customize comprehensive mathematical expressions, automatically calculate power and other test results, so as to greatly improve the test efficiency

Figure 2: key test items of LED lighting driving power supply

Figure 3: Tektronix oscilloscope with PWR power analysis module can directly display various measurement parameters to help power engineers easily complete development and testing

Table 1: three levels of oscilloscope selection that can improve the efficiency of LED driving power supply opening and testing and increase the accuracy of testing

in addition, for the excitation source, At present, Tektronix can provide pws4000/pws2000 series programmable DC desktop power supply series, which provides accurate and high-resolution constant current and constant voltage output for driving LED

PWM analysis and output ripple measurement help enter the high-end market

truly energy-saving household LED lighting products ultimately need to have dimming function. At present, they are also the demand of high-end markets such as Europe and the United States, and will be gradually popularized in other countries and markets in the future. The latest technology of LED dimming is PWM. By generating PWM signals with different pulse widths, the ratio of on and off of power devices is controlled, so as to achieve the purpose of adjusting the output luminous flux. Compared with other dimming methods, PWM dimming does not change the current flowing through the LED, and the lamp will not have color deviation, which also avoids the energy loss caused by resistance dimming and maintains the high efficiency of LED lighting

Tektronix's AFG3000 arbitrary waveform generator can easily generate PWM signals. Users can arbitrarily change the form of PWM change, the proportion of pulse width output and the change law. All operations only need to press the button on the panel, and the built-in impedance adjustment function of the generator can meet the needs of more circuits

ripple is the AC voltage added to the DC output voltage, and it is also an important measurement parameter in the LED power supply test. The higher the ripple current, the lower the power supply cost, but the light output will be affected, and the junction temperature of LED will be increased, which will affect the performance of LED, and even seriously reduce the service life of LED (experience shows that the service life of LED will be shortened by half every 10 ℃ rise in junction temperature). Therefore, it is very important to measure the ripple accurately. The power supply test scheme of Tektronix oscilloscope has the ripple measurement function, which can complete the measurement of ripple parameters with one key. For high-end applications, Tektronix tcpxx series current probes can provide ripple current measurement accuracy as low as 1mA. For low-cost applications, there are also corresponding cost-effective probes to choose from

in addition, if engineers want to complete the ripple measurement task through a simple digital multimeter, tech can also provide the corresponding scheme. Dmm4040/4050 digital multimeter has the function of double parameter measurement, which can display the AC voltage or current components at the same time. Its dual degree function, trend chart and histogram function facilitate users to detect output changes for a long time; Through the front and rear panel input function, users can alternately measure two groups of data for comparison. (end)

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