Re: CoB LED filament analysis

From	Bill Sloman <bill.sloman@ieee.org>
Newsgroups	sci.electronics.design
Subject	Re: CoB LED filament analysis
Date	2026-04-22 03:54 +1000
Organization	A noiseless patient Spider
Message-ID	<10s8dkd$1mbf8$1@dont-email.me> (permalink)
References	<20260411a@crcomp.net> <20260421a@crcomp.net> <3c6fuk16nn9tfhj24q3ulue347ab93jvh8@4ax.com> <on6fukd6chfua8nm2puqkdc6llb2jbatub@4ax.com> <20260421b@crcomp.net>

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On 22/04/2026 2:55 am, Don wrote:
> john larkin wrote:
>> john larkin wrote:
>>> Don wrote:
>>>> Don wrote:

<snip>

>> 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.

Seems unlikely. It's more likely bad triggering from a 
not-all-that-closely related waveform.

>      A silicon device that presents a capacitive 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.

The internal capacitance won't be anything like big enough to show up at 
mains frequency

The likeliest explanation is a bunch of LEDs connected in series with a 
current limiting resistor between each LED. You'd put in four mains 
rated diodes to rectify the current going through the LED/resistor 
string as the applied voltage switched direction.

Close to zero and 180 degrees the mains voltage isn't high enough to 
push any current through the LEDs, but they will start turning on at 
about 20 degrees, and progressively more of the voltage will get soaked 
up by the resistors until the voltage peaks at 90 degrees/270 degrees.

The LEDs and the resistors will heat up a bit during each half cycle - 
more in the middle of the string than at the ends, and that will make 
the current lumpier than you'd expect from a pure sine wave.

It won't make much difference to the resistors but LED forward voltage 
drop is a function of both current and the die temperature, and as the 
junction gets hotter the forward voltage drops by about 2mV/C

The LED/resistor load  also going to make current less sinusoidal than 
the mains supplier would like.

-- 
Bill Sloman, Sydney

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CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-12 05:34 +0000
  Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-12 10:45 +0100
    Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-12 10:48 +0100
      Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-12 10:50 +0100
        Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-12 12:03 +0100
          Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-12 04:44 -0700
  Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-12 04:19 -0700
  Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-13 07:40 +0000
    Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-13 01:46 -0700
      Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-13 11:40 +0000
        Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-13 14:31 +0100
          Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-13 06:59 -0700
            Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-14 12:25 +0000
              Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-14 14:04 +0100
              Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-14 08:21 -0700
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-15 02:48 +1000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-14 11:14 -0700
                Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-14 19:25 +0100
                Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-14 19:43 +0100
                Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-14 20:19 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-14 12:54 -0700
                Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-14 19:42 +0100
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-14 12:57 -0700
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-14 13:02 -0700
                Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-14 21:29 +0100
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-14 19:10 -0700
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-15 11:36 +0000
                Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-15 12:35 +0000
  Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-21 14:39 +0000
    Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-21 08:41 -0700
      Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-21 08:54 -0700
        Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-21 16:55 +0000
          Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-22 03:54 +1000
            Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-21 21:05 +0000
              Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-21 17:03 -0700
          Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-21 12:26 -0700
            Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-22 01:44 +0000
              Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-21 19:16 -0700
            Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-24 13:37 +0000
              Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 07:55 -0700
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 08:04 -0700
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-24 16:43 +0000
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-24 20:15 +0000
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-26 03:45 +1000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-25 11:14 -0700
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-25 22:56 +0000
                Re: CoB LED filament analysis ehsjr <ehsjr@verizon.net> - 2026-04-25 21:33 -0400
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 02:18 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-25 20:08 -0700
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 04:44 +0000
                Re: CoB LED filament analysis Arie de Muijnck <noreply@ademu.nl> - 2026-04-26 13:03 +0200
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 11:35 +0000
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 11:43 +0000
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 16:44 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-26 10:17 -0700
                Re: CoB LED filament analysis Arie de Muijnck <noreply@ademu.nl> - 2026-04-26 19:58 +0200
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 19:22 +0000
                Re: CoB LED filament analysis Jeroen Belleman <jeroen@nospam.please> - 2026-04-26 20:30 +0200
                Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-26 18:24 +0100
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-26 17:52 +0000
                Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-26 19:17 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-25 20:10 -0700
                Re: CoB LED filament analysis Jeroen Belleman <jeroen@nospam.please> - 2026-04-24 22:23 +0200
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 15:42 -0700
                Re: CoB LED filament analysis Jeroen Belleman <jeroen@nospam.please> - 2026-04-25 10:53 +0200
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-26 12:05 -0700
                Re: CoB LED filament analysis piglet <erichpwagner@hotmail.com> - 2026-04-26 19:20 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-27 12:49 -0700
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-27 17:04 +1000
                Re: CoB LED filament analysis Jeroen Belleman <jeroen@nospam.please> - 2026-04-27 10:59 +0200
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-27 08:11 -0700
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-28 01:51 +1000
                Re: CoB LED filament analysis Jeroen Belleman <jeroen@nospam.please> - 2026-04-27 21:40 +0200
    Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-22 16:36 +0100
      Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-22 17:10 +0000
        Re: CoB LED filament analysis JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-22 18:17 +0100
          Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-22 17:31 +0000
            Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-22 18:14 +0000
              Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-22 11:23 -0700
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-22 18:43 +0000
                Re: CoB LED filament analysis Jeroen Belleman <jeroen@nospam.please> - 2026-04-22 23:50 +0200
          Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-22 11:24 -0700
            Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-23 17:22 +1000
              Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-23 07:58 -0700
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-23 17:15 +0000
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-23 21:26 +0000
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-24 02:53 +0000
                Re: CoB LED filament analysis John R Walliker <jrwalliker@gmail.com> - 2026-04-24 18:19 +0100
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 10:39 -0700
                Re: CoB LED filament analysis John R Walliker <jrwalliker@gmail.com> - 2026-04-24 21:39 +0100
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 15:19 -0700
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-25 15:23 +1000
                Re: CoB LED filament analysis "Don" <g@crcomp.net> - 2026-04-24 17:45 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 11:12 -0700
                Re: CoB LED filament analysis Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2026-04-24 18:30 +0000
                Re: CoB LED filament analysis john larkin <jl@glen--canyon.com> - 2026-04-24 11:42 -0700
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-25 15:49 +1000
                Re: CoB LED filament analysis Bill Sloman <bill.sloman@ieee.org> - 2026-04-25 15:47 +1000

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