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Webinar: Simple Ideas to Make EMI Issues a Thing of the Past

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Sides from David Bourner's EMI webinar.

The consequences of poor design may not show up until compliance testing, which makes this a particularly stressful time as failure may require expensive and time-consuming redesign work to be carried out. Fortunately, the things engineers need to do if they want to reduce the chance of EMI issues causing problems during compliance testing are simple and straightforward.

Published in: Engineering
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Webinar: Simple Ideas to Make EMI Issues a Thing of the Past

  1. 1. 1 Simple Ideas to Make EMI Issues a Thing of the Past David Bourner Senior Applications Engineer December 2016
  2. 2. 2 Orientation › The system you are designing is complex – the many different parts have to work as one – Power connectors, cables – Modules – Circuit boards – Components: Analog , digital, electromechanical – Backplane, chassis, enclosure › Design time, components and resources are always limited › Control of CE - conducted emissions - easy to overlook › Maximum permitted energy levels extremely small › RE - radiated emissions - are measured across many more decades of frequency compared with CE – RE suppression applies to the complete system application
  3. 3. 3 Aspects of EMI Control in Switched Mode Power Systems › Elements of a SMPS › Causes of “noise” in power trees › Noise energy management principles › Some noise control practices at work
  4. 4. 4 Let’s look at a SMPS (Switched Mode Power System) Output filtering, Hold-up cap bank External OCL Load switch Load Surge and transient protection Holdup Cap bank Conducted Emissions Filtering DC-DC Converter Output / remote sensing Redundant switching circuitry Input sensing OVP/ OCP circuits Source(s) and Redundant switching circuits CM and DM noise current control area Bold arrows show DC power flow noise energy flows are different
  5. 5. 5 DCM - DC Module: From Module to Application DCM (DC Module) Evaluation board New Vicor Packages VIA: Vicor Adaptor ChiP: Converter housed in Package Double-clamped ZVS power cell +OUT -OUT Proprietary Buck-boost control +IN -IN
  6. 6. 6 Voltage Across and Current In DCM Primary Winding › ZVS eliminates the discontinuities seen in hard-switched converters › Resulting frequency spectra show this No need for external clamps or snubbers – but other parts will need to be added, external to converters
  7. 7. 7 EMI Noise Spectrum: Classifying Noise in a SMPS Control loop bandwidth not visible Switching fundamental term + harmonics RE 30 MHz – 1GHz UNFILTERED EMI PEAK SCANS - CISPR 22 - 270 VDC, 10% of Full Load, Red Lead MODEL #MDCM270P280M500A40 CE 150 kHz – 30 MHz
  8. 8. 8 EMI Coupling Mechanisms › Inductive coupling 𝑽𝒊𝒏𝒅 = −𝑳. 𝒅𝒊 𝒅𝒕 – Voltages induced with inductive coupling increase with frequency, permeability and proximity › Capacitive coupling 𝑰𝒄𝒂𝒑 = 𝑪. 𝒅𝒗 𝒅𝒕 – Currents induced in adjacent conductors increase with frequency, permittivity and proximity
  9. 9. 9 Keys to Control of EMI › Switching causes noise - couples in two modes: – Common mode and differential mode › Confine noise currents within smallest possible loop areas Use: – Y caps for common mode control › X caps for differential mode control › These are selected and connected in such a way as to preserve safety in accordance with various classifications e.g. Y1, Y2 Note the central area of the block diagram (slide #4) Apply noise control at the converter itself
  10. 10. 10 Simplified Model of the Converter Input Power Port › Common-mode AC voltages Vcm1, Vcm2 and a differential mode AC voltage source Vdm › Cs1 and Cs2: parasitics › Small loop area current pathways required for both the common and differential mode currents Cx Cy1 Cy2 shield plane Cs1 Vcm1 ~ Vdm ~ Vcm2 ~ Front-end of DC-DC converter Cs2 Suppression of pervasive noise must be effective
  11. 11. 11 EMI Control Concepts › There is a critical order to EMI control component placement. As much of the CE noise is to be conducted back to its origin. Block and bypass noise from the converter input port toward the input power source – X and Y capacitors are HF energy suppressors – place them close to converter – Surge and transient protection may affect X and Y cap action › The negative impedance of the converter - if unchecked - will produce input power bus instability › Input filter damping helps dissipate EMI noise energy and assures stable operation On the input side of the system we note that: The input holdup caps provide bus stability due to ESR
  12. 12. 12 Noise current pathways change with frequency AC source VIAs going through substrate, to solid ground plane trace on topside of board lower end of each via makes good electrical contact to the ground plane, the brown solid layer At LF --- circuit completed through straight segment of ground plane between the via contacts there, through minimum resistance path At HF --- circuit completed in image traces in the ground plane, through minimum inductance path resistive load ~
  13. 13. 13 Glimpse of CE for a standalone PRM/VTM power tree PRM switches at ~1.3 MHz VTM switches at ~ 1.6 – 1.9 MHz Common mode input noise spectrum at PRM black power terminal Note that the oscilloscope traces are measured in limited (20 MHz) bandwidth
  14. 14. 14 28V PWR SOURCE + _ M-FIAM7B + _ EMI GND FIAM BASEPLATE + _ + _ PRM L2 R VTM + _ +12 VDC DC_RTN MP028F036M12AL / MV036F120T100 TEST FIXTURE CE CONTROL ARRANGEMENT 28V RTN lL1a lL1b 28V lL3 SHIELD PLANE (COPPER BENCH TOP) CY1(a,b) CY2(a,b) CY3(a,b) CX1 CY4(a,b) CX2 CX3 Notes --------------------------------------------------------------------------------------------------- Y and bypass caps CY1(a,b), CY2(a,b), CY4(a,b): 4.7 nF HV safety caps Vishay VY1472M63Y5UQ63V0 or equivalent CY3(a,b): 4.7 nF 250v a.c. rated part Vicor part number #01000 X-caps CX1: 1000uF 63V rated ALEL paralleled with two 2.2 uF 50V rated ceramic caps CX2: two paralleled 10uF 25V rated ceramic caps, parallel 4.7nF HV cap added CX3: four paralleled 10 uF 25V rated ceramic caps ----------------------------------------------------------------------------------------------------------------- Inductors (all based on the Coilcraft SLC7530D-101ML power inductor) L1a, L1b one winding each for common-mode choke implementation L2, L3 series connection of each winding in the part Detuning resistor R 1206 sized 10 W resistor for detuning An example of a line-up for controlling CE
  15. 15. 15 Simple lab-based CE check outcome Test setup – prototype built up with FIAM, PRM (Pre-regulator) and VTM (isolated Voltage Transformation Module) Zero input test FFT CM FFT spectrum PRM black power terminal
  16. 16. 16 Implementing RE Control Detecting noise sources in the system in the near H field Cable harness design and placement; Use twisted wire, ribbons or coaxial cable. Apply CM filtering to harnesses to minimize RE. Grounding of heatsink turns it into a shield
  17. 17. 17 Checklist for Addressing EMI Concerns › Design for EMI from the beginning; know what performance you require › Select components, circuits with EMI in mind › Plan your PCB layout – Board stack-up: ground planes to be located close to matched power and signal trace layers – Assign placements for filters, SMPS modules, analog/digital circuits and returns › Determine cable harness design – select connectors – consider their placement › Plan Grounding Strategy at component, circuit, module, circuit card and system level › Filters: verify ratings, use correct components, keep input & output routes separate › Shielding: select materials appropriate to noise spectrum, target usage: look for gaps, openings and deploy conductive gaskets (critical gaps < λ/20 guide) › Use the schematic as tool to document EMI control design – Apply a flow check to ensure assignment of appropriate in-circuit control measures – Ensure that the input filtering design is conducive to input power bus stability › Carry out EMI pre-assessments continuously as the design progresses
  18. 18. 18 Acknowledgments - Question Session Special thanks to the very patient Vicor folks who helped me out with this project Scott Lee Hannes Schachenmayr Bob Pauplis Chris Swartz Arthur Russell Harry Vig Joe Aguilar Ankur Patel Peter Makrum Mike DeGaetano Vamshi Domudala
  19. 19. 19 IEEE PDH Information › Code: 1206SOL › Link for form: http://fs25.formsite.com/ieeevcep/form36/index.html

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