A fully floating BJT-based LED current driver

From	"Don" <g@crcomp.net>
Newsgroups	sci.electronics.design
Subject	A fully floating BJT-based LED current driver
Date	2026-04-09 09:17 +0000
Organization	A noiseless patient Spider
Message-ID	<20260409a@crcomp.net> (permalink)
References	<6tltskde2lkpbo4s5g44ujar7b2tttk0k9@4ax.com> <18a493794d041b26$1$2982030$4226dc73@news.newsgroupdirect.com>

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someone wrote:
> If you stand back from the microscopic current mirror circuit
> interpretation, the transistor equivalent of the DIAC using Q2,4,3,
>  with a threshold of 2.5V or so, comes into focus. Then add in some
>  current limiting/ regulating resistors here and there, and you end
>  up with the floating current source. The BC557C has an absurdly
>  small Early voltage and RCE, combined with the 'C' version beta in
>  the range of 200-800, and start-up is a done deal. Voltage compliance
>  shouldn't be a serious issue for driving LEDs, but it would be nice
>  to see an analytic to that effect. AI hasn't penetrated deeply enough
>  into our freebie CADs to give us that capabilty, so we're stuck with
>  looking at graphs.

Excellent! Your circuit suggests some silicon secrets pertinent to the
120 VAC LED COB filaments mentioned by me elsewhere:

Allow me to transition this topic to 120 VAC LED COB filaments. This
picture shows such specimens, with the topmost powered-on and the
bottommost powered-off:

  <https://crcomp.net/led/accob.png>

The protoboard's black wire connects to 120 ACV Line while its white
wire connects to Neutral. My goal is to discover the silicon secrets
in such a simple filament.

-- 
73, Don, KB7RPU                                           veritas    _|_
                                                          liberabit   |
https://www.qsl.net/kb7rpu                                vos         |

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silly circuit john larkin <jl@glen--canyon.com> - 2026-04-02 13:56 -0700
  Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-03 16:45 +1100
    Re: silly circuit piglet <erichpwagner@hotmail.com> - 2026-04-03 06:47 +0000
      Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-03 04:31 -0700
      Re: silly circuit "Don" <g@crcomp.net> - 2026-04-08 15:51 +0000
    Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-03 08:20 -0700
      Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-04 03:10 +1100
        Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-03 09:29 -0700
          Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-04 04:48 +1100
            Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-03 14:07 -0700
              Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-04 17:33 +1100
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-04 03:59 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-05 00:35 +1100
                Re: silly circuit someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-04-09 03:30 +0000
        Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-03 13:27 -0400
          Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-04 17:22 +1100
  Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-04 18:07 -0700
    Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-05 12:24 +1000
      Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-04 19:37 -0700
        Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-05 14:14 +1000
          Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-05 01:10 -0400
            Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-05 01:57 -0700
              Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-06 02:59 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-05 10:10 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-06 03:47 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-05 11:02 -0700
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-05 14:07 -0400
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-05 12:23 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-06 15:01 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-06 07:25 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-07 03:47 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-06 12:08 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-07 16:34 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-07 11:02 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-08 23:28 +1000
                Re: silly circuit piglet <erichpwagner@hotmail.com> - 2026-04-08 16:13 +0000
                Re: silly circuit piglet <erichpwagner@hotmail.com> - 2026-04-07 15:58 +0100
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-07 09:00 -0700
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-08 23:48 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-08 09:41 -0700
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-06 11:56 -0400
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-07 03:55 +1000
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-06 14:12 -0400
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-07 16:05 +1000
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-07 09:27 -0400
                Re: silly circuit Bill Sloman <bill.sloman@ieee.org> - 2026-04-08 01:53 +1000
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-07 09:06 -0700
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-07 12:46 -0400
                Re: silly circuit john larkin <jl@glen--canyon.com> - 2026-04-07 11:31 -0700
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-07 16:06 -0400
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-07 16:12 -0400
                Re: silly circuit JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-08 00:50 +0100
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-07 22:35 -0400
                Re: silly circuit "Edward Rawde" <invalid@invalid.invalid> - 2026-04-05 22:16 -0400
            Re: silly circuit piglet <erichpwagner@hotmail.com> - 2026-04-05 22:27 +0100
  Re: silly circuit someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com> - 2026-04-09 03:45 +0000
    A fully floating BJT-based LED current driver "Don" <g@crcomp.net> - 2026-04-09 09:17 +0000
      Re: A fully floating BJT-based LED current driver JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-09 16:16 +0100
        Re: A fully floating BJT-based LED current driver "Don" <g@crcomp.net> - 2026-04-09 22:03 +0000
        Re: A fully floating BJT-based LED current driver john larkin <jl@glen--canyon.com> - 2026-04-09 16:46 -0700
          Re: A fully floating BJT-based LED current driver john larkin <jl@glen--canyon.com> - 2026-04-09 16:57 -0700
          Re: A fully floating BJT-based LED current driver "Don" <g@crcomp.net> - 2026-04-10 03:24 +0000
          Re: A fully floating BJT-based LED current driver JM <sunaecoNoChoppedPork@gmail.com> - 2026-04-10 17:34 +0100

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