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LED display electromagnetic compatibility (EMC) the most effective design and improvement methods

LED display electromagnetic compatibility (EMC) the most effective design and improvement methods


Taking into account the high-density LED display in the field of professional indoor applications more and more people on their own health and safety needs of increasingly related to health and safety of EMC design and certification is becoming increasingly important, LED display EMC design and Improve without delay.
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As we all know, light-emitting diode is a low-voltage-driven semiconductor light source, the previous outdoor display AC-DC conversion and transmission are done outdoors, far away from the crowd. And when the high-density LED display gradually into the indoors, we have to consider the process of electromagnetic radiation in a limited space accumulation.
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In order to further study the LED display EMC, select a LED display manufacturer's P2.5 display module for testing, to verify our analysis, and find the most effective LED display EMC design and improvement methods.
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According to IEC and CISPR standards, the sample test items into EMI and EMS two categories. Test results are as follows:
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(1) Test standard: EN55022: 2010 + AC: 2011 / CISPR22 (2008-09), EN61000-6-3: 2007 / A1: 2011 / AC: 2012 Test results: Conducted interference.
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(2) Test standards: EN55022: 2010 + AC: 2011 / CISPR22 (2008-09), EN61000-6-3: 2007 / A1: 2011 / AC: 2012, the test results: emission interference.
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(3) test standard: EN61000-3-2: 2006 / A2: 2009, the test results: harmonic interference.
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(4) test standards: EN61000-3-3: 2013, test results: voltage fluctuations, flicker interference.
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(5) test standard: EN 61000-4-2: 2009, test results: electrostatic discharge protection.
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(6) Test standard: EN 61000-4-3: 2006 + A2: 2010, the test results: RF electromagnetic field protection.
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(7) test standard: EN 61000-4-4: 2004 + A1: 2010, test results: transient pulse protection.
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(8) Test standard: EN 61000-4-5: 2006, the test results: surge voltage protection.
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(9) Test standard: EN 61000-4-6: 2009, test results: conducted interference protection.
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(10) Test standard: EN 61000-4-8: 2010, test results: power frequency magnetic field protection.
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As the LED display product itself using high-end switching power supply, with transient voltage suppressors, wiring specification, from the test results can be obtained in addition to the launch, the other tests were passed, therefore, LED display products through the launch EMC certification needs to overcome the key issues.
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According to the previous measurement data, LED display switching power supply, control card and internal signal transmission will have different degrees of electromagnetic radiation.
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In addition, LED display works by adjusting the LED current pulse parameters to achieve high gray, high refresh, therefore, the higher the refresh rate of the display screen, the system card signal frequency also increases, resulting The stronger the radiation interference, which is the inevitable result of high-quality display applications, but also the display of the most important sources of electromagnetic disturbance.
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The internal signal cable input and output lines, power input and output lines, from the switching power supply and the control card on the electromagnetic radiation generated in the internal cable coupling between the formation of radiation channels, the final conduction out of the formation of conduction interference, which Part of the radiation most easily overlooked, but it is an important part of radiation emission, for which we can take the following measures were tested.
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1, shielding
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Through testing, found the module and the system adapter board signal connection between the flat cable is the focus of rectification object. At first by increasing the magnetic ring, the peak was a certain inhibition, but the effect is not obvious.


2, filter
Field test, the module power supply VH2 at the increase of a 3300uf electrolytic capacitors and found that the inhibition of radiation is obvious, especially in the 30MHz to 1000MHz range of glitch and energy spectrum of the inhibition was obvious. The larger the capacitance, the greater the suppression of the glitch spike, and the smoother the smoothed curve. Of course, the choice of capacitance value in accordance with the actual design requirements to be.


3, formation shielding
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When the transfer plate from the original two-layer board to four layers, that is, an increase of the top and bottom of the ground layer, this can also be on the circuit radiation protection.
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When the LED surface array driver board to increase the two-tier ground, from the original four-layer board into six layers, can play a better role in preventing radiation. When the edge of the transfer plate with the entire side of the copper foil, and metal box with a screw fastening to form a shell, so as to achieve the role of shielding the signal.


4, reduce the product supply voltage
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Because conduction, radiation and dv / dt or di / dt is proportional to the value, so the higher the voltage, conduction, radiation, the greater the value. Sample supply voltage is 4.6V, when the voltage adjustment for the 4.2V, the experimental data can be seen, found that spikes can also be a certain improvement.


5, optimize the product structure
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Taking into account the radiation and the largest aperture size, when the hole spacing is much larger than the hole diameter, the shielding effect can be greatly improved, so the back cover of the original slot for long elliptical hole changed to 554 diameter hole.
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6, to improve product technology
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The original sample back cover for the ordinary plastic parts, improved coating for the back cover plus the same time, the use of plastic silver copper conductive paint, screw and the whole box connected, making the diagonal measurement of spray resistance is not greater than 20 ohms, This process improvement, but also a better protection from radiation.
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7, multiplier
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As the LED display GCLCK signal effects such as the refresh rate of the display, so by changing the size of GCLCK value to achieve the purpose of reducing, but from the actual experiment, we found that the value of the multiplier has little effect. This improvement in reality is not desirable.
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in conclusion

Through the above-mentioned repeated testing, improvement, re-test, the sample finally passed the radiation detection, the improvement work is very successful, but also for other LED display EMC rectification work to find a reference method.
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By improving the length of the flat cable, the power supply V to increase the appropriate large-capacity electrolytic capacitors, reducing the supply voltage of the product, formation shielding, optimize the product structure, improve product technology and other means, at the beginning of the LED display design, you can avoid a lot The existence of EMC problems, reduce the amount of work to improve and improve product design success rate.


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