Can an ESD create a current path? - Page 1
Forum section: electronics / beginners

author: int6h
author_rank: Newbie
timestamp: August 02, 2018, 10:07:23 pm
content: Since plasma is conductive, can a spark of ESD create a current path in a spark gap?

author: CopperCone
author_rank: Super Contributor
timestamp: August 02, 2018, 10:09:52 pm
content: yes look at tubes like krytron

author: int6h
author_rank: Newbie
timestamp: August 02, 2018, 10:35:53 pm
content: Thanks for the answer.Can it be dangerous for HV electronics? I mean, you're not supposed to put your finger in there anyway, but other surfaces can also create ESD.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 03, 2018, 01:51:53 am
content: Absolutely. Watching lightning real close.

author: exe
author_rank: Unknown
timestamp: August 03, 2018, 03:59:35 pm
content: I think so, check this out:(spoiler alert: exploded light bulb destroyed MCU)

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2018, 07:54:22 pm
content: The closest example I can think of, off hand, is old CRT TVs. I remember reports in repair magazines where a low current EHT flashover had triggered a very destructive arc across the low voltage HT mains derived supply.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2018, 01:37:05 am
content: That is exactly how triggered spark gaps work.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 06, 2018, 09:08:48 am
content: Quote from: Gyro on August 03, 2018, 07:54:22 pmAh, but that's probably not "low current", because EHT is supported by the ~500pF capacitance of the CRT glass. Indeed, HV strikes in CRTs were a not-infrequent occurrence -- due to impurities flaking off inside the bulb, or excess gas -- and ESD protection was usually seen, usually a GDT (or three) on the socket.I traced the signal path in a Trinitron monitor once, it's got one GDT for each cathode (the cathodes are driven with video, about 50V at ~100MHz bandwidth), and series carbon comp resistors (presumably, the lowest value possible without impairing the bandwidth, 22 ohms). The driver itself has small clamp diodes, so there's double protection. The driver is a bipolar IC, internally an emitter follower driving the output pins; it would have some capability for transient handling, but not much considering the small feature size of high voltage RF transistors used. In short: it's designed to withstand, essentially, 30kVmachine modelESD, while maintaining a 100MHz analog bandwidth -- a challenge by any means!Tim

author: Gyro
author_rank: Super Contributor
timestamp: August 06, 2018, 11:08:18 am
content: QuoteYes indeed!Irrc, these reports were more along the lines of poorly routed / degraded / dirty EHT leads and intermittent tube outer coating ground spring connections arcing to the board - older cheaper stuff. Internal tube flashover to cathode(s) were normally better protected, even on the cheaper sets (PCB slot gaps etc.)EDIT: Useless unrelated fact warning: B&O used to use Philips southern hemisphere CRTs upside down to move the EHT cap to the bottom, thus enabling them to thin down the cabinet profile at the top. Unfortunately this lead to rather close proximity between the EHT connection and the electronics.