Path: csiph.com!eternal-september.org!feeder.eternal-september.org!nntp.eternal-september.org!.POSTED!not-for-mail From: "Don" Newsgroups: sci.electronics.design Subject: Re: CoB LED filament analysis Date: Tue, 21 Apr 2026 16:55:37 -0000 (UTC) Organization: A noiseless patient Spider Lines: 59 Message-ID: <20260421b@crcomp.net> References: <20260411a@crcomp.net> <20260421a@crcomp.net> <3c6fuk16nn9tfhj24q3ulue347ab93jvh8@4ax.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Tue, 21 Apr 2026 16:55:38 +0000 (UTC) Injection-Info: dont-email.me; posting-host="55d1dd6df35d5c1e7ec3894686ebf19d"; logging-data="1744315"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+FdjDxvsMm8sDGMVr7sD1I" Cancel-Lock: sha1:xLl9QT127NPdPybCg58fylAEaUs= Xref: csiph.com sci.electronics.design:743198 john larkin wrote: > john larkin wrote: >> Don wrote: >>>Don wrote: >>>> Recent thread topic transitioned to a tentative opinion on a work-in- >>>> progress webpage: >>>> >>>> >>>> >>>> Radiography imparts interesting insight. Second opinions welcome! >>>> The current waveform flopped. Any advice on how to use a Fluke >>>> 80i-1000s connected to a Tek 2465B to display the 120 VAC current >>>> wave is appreciated in advance. Also, what does "P2 < P1" signify on >>>> the current probe? >>> >>>Alright you guys, a couple of current curve images are now available on >>>the webpage. For the present case, in regards to the probe's "P2 < P1" >>>orientation decal, P1 designates Line while P2 indicates Neutral. >>> The probe provides a sharper, cleaner curve compared to the >>>resistor. Both curves illustrate how the silicon filament primarily >>>presents itself as a capacitive load. >>> The filament's high voltage combined with its low amperage degrades >>>resistor curve quality. It took a 10 M ohm resistive current sensor for >>>the half-wave rectification effect to become visible. >>> The probe curve's mostly blue trace shows the peak-to-peak Line >>>voltage. It's used to properly trigger the scope. (Perhaps the scope's >>>line trigger accomplishes the same result with less effort?) The probe >>>curve's mostly green trace shows the current, with peaks and valleys >>>created by half-wave rectification at each end of the filament. >>> The current curve is set to 2mV per division. Does anyone know how >>>to transpose it to mA? >> >>It can't be capacitive. It has no mechanism to store energy. >> >>Unless one of the thingies on the end is a cap. A DC curve would >>resolve that. >> >>A thermal image would be interesting too. >> > No, it lights up with DC, so there's no series cap. ELI the ICE man. The trace of the current curve clearly leads the voltage trace, so the filament must present a capacitive load. A silicon device that presents a capactive load is different from a series capacitor: COB LEDs present capacitive loads through parasitic capacitances inherent to their densely packed chip-on-board structure. These capacitances arise between closely spaced LED dies, bonding wires, and the substrate, affecting driver circuits during switching. Danke, -- 73, Don, WD7Q veritas _|_ liberabit | https://www.qsl.net/wd7q vos |