Dear member of the Land & Naval Defence Electronics Division, Linear regulators, where the input is the output of a SMPS, are subject to the limitations of the PSRR of the 78xx regulators; typically less than 20dB above 40kHz. Even if no SMPS, then the typical 78/79XX does little for the 'ambient' stuff > 100kHz. As efficiency should not be a principle design factor, avoid SMPS in general, and switching LED drivers in specific; unless you need a wide-spectrum noise source...
Recently, had to replace the incandescents in my employer's humble chamber. My solution was a discrete version of a LDO regulator configured for CC, where the reference voltage was buffered and filtered and the op amp that drove the series-pass mosfet was 2d order filtered. The mains power is from a transformer model chosen for its inherent shielding and capacitive coupling rating, and each bridge diode had a good (class II ceramic) capacitor. Output of Bridge through a pi filter. Essentially no noise, except what CM stuff manages to get coupled into the long DC power lines to the LEDs. The LEDs themselves can be a bit of a source noise if they get too warm, but this can be decoupled, and seldom a problem if good CC source used (CV sources cause shot noise and perform poorly with LEDs). An easier solution would be to use one the new LDO regulator designs, but be wary of those using noisy bandgap references. TI and LT have some app notes on linear current sources. Brian Member of the Desert Naval Cacti Offense Division -----Original Message----- From: Price, Andrew (Leonardo, UK) [mailto:andrew.p.pr...@leonardocompany.com] Sent: Wednesday, November 22, 2017 4:01 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Use of LED Spots in EMC Chambers [General Use] Hi all. Has anyone had experience with using LED Spot lamps in EMC Chambers? What types/manufacturers would be recommended? Would appreciate help in trying to solve someone's problems with noise during radiated emissions. Test Facility has just had all their chambers converted to LED Spots and they are suffering broadband noise issues. Regards Andy Andrew Price Land & Naval Defence Electronics Division Prinicpal Environmental Engineer (EMC) Leonardo MW Ltd Sigma House, Christopher Martin Rd, Basildon SS14 3EL, UK Tel EMC LAB : +44 (0)1268 883308 Mobile: +44 (0)7507 854888 andrew.p.pr...@leonardocompany.com<mailto:andrew.p.pr...@leonardocompany.com> leonardocomapany.com - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> 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 <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
