George, The LCD itself does not usually use high voltages, but most are supplied with a fluorescent tube backlight. This is usually driven by a high-frequency (50+ kHz) oscillator with an output designed to deliver an open circuit voltage in the low kilovolt range to strike the tube, followed by a constant running current at a lower voltage. Maybe this is what is causing the emissions.
Kind regards, Geoff Lister Senior Engineer Motion Media Technology Ltd., Bristol, UK. http://www.motion-media.com -----Original Message----- From: George Stults [mailto:[email protected]] Sent: 29 June 2001 01:21 To: '[email protected]' Subject: LCD Monitors etc. Hello All, I have theorized that a Liquid Crystal Display (LCD) monitors should have less radiated emission than a comparabe CRT (same viewing area) since there is no high voltage tube and high powered oscillators, etc. I am wondering if anyone can confirm or deny this rumor based on actual testing. Also If there are folks in the crowd who sell LCD monitors, I would like to hear from you offline. And to follow up an earlier question that I asked the group about quiet test equipment, I did an experiment as follows: I purchased and tested a Fujitsu LifeBook B-2175 (500 MHz laptop). As a 'Best Case' I tested it stand alone, battery operated, no cables, just running MS Word with an 'HHHHHHH' pattern on the screen (I'm guessing that the pattern made no difference on the LCD screen). In that configuration, it was 4.4 dB over class B. I think the test site claims an measurement uncertainty of 4 dB. Anything else I did, connecting cables etc, made it worse. The lap top in question has a magnesium case and gives the appearance of quality construction. Given the 80/20 rule, the production process could be compliant and I wouldn't know any different, but I wonder if there is such a thing as a Class B laptop in the real world? Best Regards George Stults WatchGuard Technologies Inc. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall," --- Incoming mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.261 / Virus Database: 131 - Release Date: 06/06/01 ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
