Ferrite Bead "fix" for Electrostatic Discharge EM emissions? - Page 1
Forum section: electronics / beginners

author: chaseadam
author_rank: Contributor
timestamp: December 24, 2019, 02:37:51 am
content: Electrostatic discharge from me getting up out of my desk chair is causing my older HP LP3065 30" WQXGA screen to "disconnects" from a 2019 15" Macbook Pro. The source of the issue evaded me for a while, but I finally narrowed it down to the Electrostatic discharge (very reproducible).The monitor only takes Dual-Link DVI input, but the computer only has USB-C, so I have the following adapters in series to connect the monitor:6" aluminum USB-C to DisplayPort adapter (Aliexpress/Ebay, questionable quality)BizLink Active DisplayPort to Dual-Link DVI adapter with separate USB cable for power input3' Dual-Link DVI cable with dual ferrite beads (Amazon Basics, seems high quality)I put on a split core ferrite bead onto the 6" USB-C to DisplayPort adapter and the issue rarely occurs now. Ferrite bead was pulled off of a USB or similar cable from a while back. I recalled reading a Sony manual for a digital camera from the early 2000s regarding the huge ferrite beads on the USB cable that came with it and it mentioned EMF in addition to the ferrites on digital and analog video cables.What is this ferrite bead doing to help during an electrostatic discharge event?Is there an ideal bead to use for this purpose?Is it helping to maintain the signal integrity?Is it protecting the Macbook from excess voltage?Other information:The issue occurs with a 6' dual ferrite bead Dual-Link DVI cable (seems high quality).The issue occurs with Apple USB-C power adapter with grounding and non-grounding power cables.The shield of the male DisplayPort plug on the adapter is low resistance to ground, presumably, through the shield of the DVI cable to the shield of the monitor to the ground of the power cord.I am not touching the desk or devices when I get up from my chair when this occurs.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 24, 2019, 06:37:08 am
content: If the USB cable is poorly shielded, or the adapter is poorly constructed (to a similar end), the ferrite bead will tend to reduce the amount of interference that leaks through that shield and couples to the (USB) data lines.That's the most likely scenario based on your description, with the actual culprit potentially being anywhere along the signal chain. For example, it could even be, say, a power supply glitch resetting or locking some part; but data signals being weaker (a volt or two), they are a more likely victim.Ferrite beads don't usually do very much in this situation -- ESD is a huge signal, so it's hard to attenuate meaningfully by itself. Probably the exact combination is just marginal enough, and the combination of your seat and clothing fabrics, ambient humidity, the area and contact pressure of your butt, etc., is just teetering over that threshold.Increasing the distance between chair and PC/adapters/monitor, or rerouting or disconnecting cables that may possibly be conducting EMI between them, is another option. Or adding shields -- the difference being, a shield is purposefully (and correctly) RF-grounded to the equipment and cables, so that external EMI "splashes" over it rather than being dropped across cables and carried into/through devices. (The risetime of an ESD pulse, in terms of the speed of light, is easily about a meter long -- so a shield about the size of a desk (say if the desk were metal, and these things were carefully grounded to it), subjected to ESD, is very much analogous to ocean waves crashing over a beach!)Tim

author: chaseadam
author_rank: Contributor
timestamp: May 01, 2023, 07:29:52 pm
content: Turns out my ESD emissions are likely from a gas lift chair with metal legs. This is a known phenomenon and was even covered on EEVBLOGhttps://invidious.fdn.fr/watch?v=r-V_Z3bD_PAThis paper from 1993 (http://www.emcesd.com/pdf/eos93.pdf) hypothesizes that the ESD generated internally by the seat cushion foam returning to it's un-compressed state radiates out from the metal legs causing an extended 10-15 seconds of ESD events.displaylink FAQhttps://support.displaylink.com/knowledgebase/articles/738618-display-intermittently-blanking-flickering-or-losmentions converters exacerbate this issue.> Issues such as those mentioned above are particularly evident in video cable converters.and It specifically calls out a Ferrite Bead as something which will help> swapping video cables, especially for ones with magnetic ferrite ring on the cable, can eliminate this problem.contemporary social thread with loads of resources:https://mastodon.online/@haeckerfelix@mastodon.social/110272427846205529