Hi Istvan,
Thanks for the links to the papers (I'm certainly not a power supply expert but I'll do my best to digest them) and for your comments. The product in question is a small compute module with limited board space for filters hence the customers request to combine all the filters into one. All the best James James Pawson EMC Problem Solver Unit 3 Compliance Design for EMC / Pre Compliance / Problem Solving / EMC Testing / Consultancy / Environmental & Vibration <http://www.unit3compliance.co.uk/> www.unit3compliance.co.uk -- 07811 139957 Opening Hours: Tuesday to Friday, 0830 to 1800. Closed Monday. <https://www.linkedin.com/in/james-pawson-unit-3-compliance/> Connect with me on LinkedIn From: Istvan Novak <[email protected]> Sent: 04 June 2019 13:40 To: [email protected] Subject: Re: [PSES] DC/DC EMI Input Filter Stability Hi James, If you consider input filters for DC-DC converter inputs (not a must, but a good idea), you want to have one filter for each converter input.? In such a case if you design each converter with its own input filter to be stable, there will be no problem.? I have been designing computer systems with many DC-DC converters in the past 22 years (also up to a dozen converter inputs connected together without input filters) and there were no issues around this.? The key is not to save on high-ESR bulk capacitors connected across the input of each DC-DC converter.? In practice I have found the loop stability on the output side to be much more challenging to solve, but that should be handled differently. You can find a few additional considerations in http://www.electrical-integrity.com/Paper_download_files/DC12_11-MP2.pdf and http://www.electrical-integrity.com/Paper_download_files/DC17_PAPER_11_Overv iewComparisonPowerConverterStability_Hartman.pdf Regards, Istvan Novak Samtec On 6/4/2019 3:45 AM, James Pawson (U3C) wrote: Morning all, ? I?m designing an EMI filter for a DC input power line that has four DC/DC converters all running off it. ? I know that the output impedance of the EMI filter needs to be much lower than the input impedance of the DC/DC converter to prevent oscillation/instability. But what happens when there are multiple DC/DC converters running in parallel from the same input? How do the input impedances interact? Do they appear in parallel or do the control loops isolate stability issues to individual converters? ? My understanding from this paper - http://www.ti.com/lit/an/slua929a/slua929a.pdf - is that the control loop and output filter of the DC/DC contributes to the stability analysis. If so, then each DC/DC can be considered individually with the filter being designed to have margin to the lowest input impedance of all of the converters. This is instead of just adding all the input impedances in parallel. ? Is my understanding correct? ? Thanks in advance, James ? ? ? ? James Pawson EMC Problem Solver ? Unit 3 Compliance Design for EMC / Pre Compliance / Problem Solving / EMC Testing / Consultancy / Environmental & Vibration www.unit3compliance.co.uk <http://www.unit3compliance.co.uk/> -- 07811 139957 Opening Hours: Tuesday to Friday, 0830 to 1800. Closed Monday. ? Connect with me on LinkedIn <https://www.linkedin.com/in/james-pawson-unit-3-compliance/> ? ? - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[email protected]> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[email protected]> > - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
