Re: CoB LED filament analysis

From	john larkin <jl@glen--canyon.com>
Newsgroups	sci.electronics.design
Subject	Re: CoB LED filament analysis
Date	2026-04-24 15:42 -0700
Organization	Highland Technology
Message-ID	<4arnuklt5a6olqtb0h77fab934tg1nbov9@4ax.com> (permalink)
References	(6 earlier) <20260424a@crcomp.net> <rl0nukdg28kug1ncquik61iqb06ak4gtld@4ax.com> <rh1nukhsan6d1hkhamqvl6bqr46jv1cj11@4ax.com> <20260424b@crcomp.net> <10sgjg4$bf5o$1@dont-email.me>

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On Fri, 24 Apr 2026 22:23:32 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:

>On 4/24/26 18:43, Don wrote:
>> john larkin wrote:
>>> john larkin wrote:
>>>> Don wrote:
>>>>> john larkin wrote:
>>>>>> Don wrote:
>>>>>>> john larkin wrote:
>>>>>>>> john larkin wrote:
>>>>>>>>> Don wrote:
>>>>>>>>>> Don wrote:
>>>>>>>>>>> Recent thread topic transitioned to a tentative opinion on a work-in-
>>>>>>>>>>> progress webpage:
>>>>>>>>>>>
>>>>>>>>>>> <https://crcomp.net/ledfilament/index.php>
>>>>>>>>>>>
>>>>>>>>>>> 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.
>>>>>>>>>
>>>>>>>>> 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.
>>>>>>
>>>>>> Since the current probe waveform is so different from the one that
>>>>>> uses a resistor, one must be wrong, or likely both.
>>>>>>
>>>>>> Stray capacitances are at least six orders of magnitude from causing
>>>>>> the phase shift that you are seeing.
>>>>>
>>>>> You're wrong, no doubt about it. Stray capacitance caused my problem.
>>>>> And your sweeping generality at this juncture led me to question my
>>>>> correct quantitative instincts.
>>>>>
>>>>> "ELI the ICE man. The trace of the current curve clearly leads the
>>>>> voltage trace" leads to the correct solution.
>>>>>
>>>>> Hint: stray capacitance originates from more than one source.
>>>>
>>>> Probably the biggest capacitance is the LEDs themselves.
>>>
>>> Or the rectifier diodes. But still not much c.
>>>
>>> Measure it.
>>>>
>>>> If you used a sensible value current shunt resistor - ohms and not
>>>> megohms - the effects of the capacitance would be invisible with 60 Hz
>>>> excitation.
>>>>
>>>> Measure the capacitance and do the math. Or Spice it.
>>>>
>>>> "ELI the ICE man" is not quantitative.
>> 
>> OK, We'll do it your quantitative way. Stray capacitance is at least six
>> orders of magnitude higher than what you imagine. Because the biggest
>> capacitance does not originate with the filament.
>> 
>> There's no need to goof with a shunt resistor when an accurate current
>> probe measurement is already available:
>> 
>>      <https://crcomp.net/ledfilament/curveprobe.png>
>> 
>> It shows you everything you need to do your own math. Show me your
>> math and I'll included on my webpage, with your permission.

Iron-core current transformers get very nonlinear at low currents. The
magnetic domains get sticky. You showed a gigantic CT.

>> 
>> Hint for people who still don't see the light (so to speak): Bob Pease
>> said, "My favorite programming language is solder." On a related note,
>> Pease passionately hated one piece in particular, amid the equipment
>> found in an electronic lab.
>> 
>> Danke,
>> 
>> --
>> 73, Don, WD7Q                                             veritas    _|_
>>                                                            liberabit   |
>> https://www.qsl.net/wd7q                                  vos         |
>> 
>
>This still doesn't make sense, but you piqued me enough to make
>me do my own measurement. I don't see any phase shift between
>voltage and current, although the power factor is certainly far
>from unity. You can see my results here:
><https://cern.ch/jeroen/LEDstring>.
>
>Jeroen Belleman


Was the curve on the left done at DC?

Why is your voltage waveform flat-topped? At 100 volts?

At 30 mA, your 1K resistor drops 30 volts. So the "Voltage" connector
doesn't represent the voltage seen by the DUT.

And does the "Voltage" connector go straight into a scope channel? No
probe?

Your current waveform does have about the right shape and timing. No
time lags. 

The x-rayed COB seems to have a 4-diode bridge rectifier, two
resistors, and one string of LEDs. That is more cost effective than
having two strings, twice as many LEDs, each on half the time.


John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

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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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