I am not a power supply designer - but all of the people in this lab are -> so guilt by association.
Do not know of any commercial LED drivers that use linear converters, so you are probably stuck with SMPS noise. I made a linear driver for cactus LED array for a xmas decoration - but had to carefully feedback with both V and I to compensate for temp coeff, and it was somewhat of a monstrosity. Much RFI comes from the 'smart' controllers where there is also a microprocessor and perhaps data lines. Most modern converters operate > 20kHz, otherwise component and PCB feature size would be too large and efficiency sucks. If you are making your own, the best approach would be to use a 'dumb' converter, operate about 15kHz, use an over-sized transformer where the LC leakage negates any need for pri/sec y-caps, and LC decouple the output far away from the main converter. If you have enough margin for increased temperature and decreased efficiency, make gate drive signal edges to main switch transistor very sloooowwww. Also locate the controller and converter external to the EMC chamber. While you are at it, do not use PFC unless the converter is > hundreds of watts. It may reduce conducted emissions/harmonics, but can radiate more stuff. Brian -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of Rene Charton/Twn/TUV Sent: Friday, March 01, 2013 6:46 PM To: [email protected] Cc: [email protected]; [email protected] Subject: RE: LED Chamber Lighting - drivers outside the chamber If the multi-string controllers are switched-mode, then we have the RFI problem again. Or, can the switching frequency be set to 500 Hz, so the 10th harmonic becomes 5 kHz which is below 9 kHz ? twisting the wires will also help for the frequency range 9 kHz to 30 MHz. Rene Charton "Brian Oconnell" <oconnellb@TAMURA CORP.COM> To Sent by: <[email protected]> [email protected] cc Subject 03/02/2013 03:06 RE: LED Chamber Lighting - drivers AM outside the chamber Please respond to <oconnellb@TAMURA CORP.COM> Most mondo very mucho correct about string current imbalance. Look at reference designs by TI and others that use multi-string controllers. Brian -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of John Woodgate Sent: Friday, March 01, 2013 10:33 AM To: [email protected] Subject: Re: LED Chamber Lighting - drivers outside the chamber In message <[email protected]>, dated Fri, 1 Mar 2013, "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> writes: >I know the topics about LED current sourcing and temp coefficient, but >as my power source is limited at 3 amps, which also is the full load >current of the LEDs, there is no risk of dead LEDS due to temp runaway. >There are 10 LEDS in series and 10 of these chains in parallel. I hope you are right but 'NTC' plus 'parallel' can spell 'current hogging'. Incidentally, it's not 'luminary' (a sort of up-market celebrity) but 'luminaire'. -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk SHOCK HORROR! Dinosaur-like DNA found in chicken and turkey meals John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- 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://listserv.ieee.org/request/user-guide.html 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]>
