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I can only guess that the unusual circuitry in what would otherwise be a typical linear current regulated LED lamp is to tick a box for European requirements.
It's using a separate current regulator on the capacitor to soften the current peak at the top of the sinewave. Probably to fudge a slightly better power factor.
I'm not sure what the voltage divider is monitoring.
The addition of a high speed diode in series with the bridge rectifier output is perplexing. Is it some odd attempt at adding faster reverse recovery to the rectifier? At 50/60Hz it doesn't seem like it's needed.
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13 thoughts on “Tesco lamp with weird circuitry twist”
  1. Avataaar/Circle Created with python_avatars Richard J Lebens says:

    My guess…. the capacitor is not there to provide DC. the chip is a constant current source for the LEDs that follows the AC waveform and provides a fairly decent power factor. the capacitor is charged at a midpoint on the falling edge of the AC waveform to keep the diodes on and lessen flicker. the fast diode is there to lessen the loss of the reverse recovery of the big rectifier diodes as the input drops below the cap voltage.

  2. Avataaar/Circle Created with python_avatars Hola! Simmo PM Hunter says:

    With the active capacitor switching, the fast diode stops reverse current back into the bridge.
    The lesbian nun will allow the cap to be charged when the LED voltage/ current drops.

  3. Avataaar/Circle Created with python_avatars der.Schtefan says:

    Come come, you can't complain in every second video how the power companies are going to charge us for reactive power soon with their devilish smart meters, and when you then get a lamp (which will be installed maybe 10 times in one's house) that does nice PFC you call it "European Bureaucracy".

  4. Avataaar/Circle Created with python_avatars Joseph E says:

    The lamp is rated at 7. 3 W but what is the actual consumption?

  5. Avataaar/Circle Created with python_avatars twocvbloke says:

    A "Lesbian Nun Input", now there's an interface that needs to become a standard… 😛

  6. Avataaar/Circle Created with python_avatars imark7777777 says:

    I'm probably not the first to say it but I wonder if the diode has to do with the dimming?

  7. Avataaar/Circle Created with python_avatars Gazza Macca says:

    LN Lesbian Nun. Very electronic music group name. 🤣

  8. Avataaar/Circle Created with python_avatars Slikx666 says:

    Clive. They made it that way to impress you. They knew that you would take one apart. 😄👍

  9. Avataaar/Circle Created with python_avatars Hungry Horse says:

    I've seen a few lesbian nuns on a stag do once, that was a great show.

  10. Avataaar/Circle Created with python_avatars CyberWomble says:

    Hmm, I wonder what fun you could have with the Nothing Phone and its 900 LED's?

  11. Avataaar/Circle Created with python_avatars Ferrum Ignis says:

    The LN terminal is measuring the difference between the rectifies supply rail and the LED Vf. This is almost certainly used to control the capacitor charge current, i.e. make it proportional to voltage so the circuit appears resistive, at least during the portion of the AC waveform where the cap is charging.

    Modifying the lamp to reduce LED current will probably upset this; with less current the ripple on the capacitor and therefore conduction angle will be reduced which would degrade PF. Probably the ~5 ohm resistor needs to be adjusted accordingly.

  12. Avataaar/Circle Created with python_avatars L4b3n says:

    I guess Pin 8 is Vcc and the divider is there to limit the voltage. The only reason for the additional diode is probably that the leakage current of the bridge rectifier diodes is to high and therefore a additional diode is added. But it really doesn’t make sense at all …

  13. Avataaar/Circle Created with python_avatars Dry Roasted says:

    Watch out for Lesbian Nuns! 🤣

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