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Thread: Making a flickering LED filament bulb (flame simulation) - what transistor for 60V?

  1. #1

    Default Making a flickering LED filament bulb (flame simulation) - what transistor for 60V?

    I would like to modify a bulb containing LED filaments (example image below) so that some of the filaments flicker, kind of like a flame. I intend to use flickering 3mm LEDs to control the flickering. Flickering LEDs contain a tiny IC inside the epoxy which cause them to flicker. I also want the bulb to be activated by a PIR sensor. I will have to carefully open the bulb and break/make some electrical connections.

    I think the filaments accept 10-15 mA at 50-60 V.

    Could I use a BC337-25 transistor for this? The voltage across everything is really high but I'm not sure that matters since the LEDs drop it all and the current is maximum 15 mA. If the transistor is closed, is it trying to hold back the entire 60 V? In that case what would be a suitable transistor which is small and cheap and not overkill? The max collector-emitter voltage for BC337-25 is 45 V.

    I could put the flickering LED in series with the filament or I could use it to turn the transistor on and off? I don't know which is better, if either?

  2. #2
    Join Date
    Jan 2004
    Pleasanton (Bay Area), CA, USA

    Default Re: Making a flickering LED filament bulb (flame simulation) - what transistor for 60

    Very innovative approach.

    I am not an expert - really just a beginner who has failed on making circuits a few times, so take this for what it is worth.

    An alternative method of making it flicker is to use a 555 timer chip with a sensor attached to the control pin. That might be easier than taking apart a flickering LED to get to the circuit, and would provide a way to alter the frequency to your choosing. My guess is that someone has already built a similar setup with a 555 timer and you could use ideas from their circuit to double check your own design - even if you stay with the led trigger method.

    It isn't clear to me if you need a transistor driver in between the LED / 555 timer and the actual on/off transistor or not, but I suspect that you do.

    I think that part of making this work will depend on how you ground or don't ground (float) some of the components. The voltages required are based on relative voltages, not absolute voltages, so it is possible that a battery driven setup that is isolated from the LED string voltages could work.

    Perhaps a mod will move this thread to the electronics / battery section, as it is a perfect question for that area. PM the mod in charge of this section and ask if they think it would fit better there. Please don't re- post, that is frowned upon.

    Sorry for the poor quality answer, but perhaps there is enough info to look further.
    Last edited by HarryN; 11-16-2017 at 09:35 AM.
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  3. #3
    Flashaholic* DIWdiver's Avatar
    Join Date
    Jan 2010
    Connecticut, USA

    Default Re: Making a flickering LED filament bulb (flame simulation) - what transistor for 60

    Golly, that might just work.

    Except that it will fry your transistor. When the transistor is turned on, it will see almost no voltage at all, but when it is off, it will see the full power supply output voltage. If it's around 60V when the LEDs are lit, it will be somewhat higher than that when they are not.

    Some better choices would be 2N5550, 2N5551, BC63916, MPSA06.

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