LED Light Bulbs Running Directly from Wall Current? - Page 1
Forum section: electronics / beginners

author: DrDeke
author_rank: Contributor
timestamp: July 23, 2017, 05:29:31 pm
content: I moved recently and found some light fixtures in the new house with "candelabra base" (smaller than the normal light bulb screw connector) sockets containing incandescent bulbs. I replaced these with some "classic filament" style LED bulbs that I bought at a local retailer, and noticed that the new bulbs have a pretty strong strobe/flicker effect when in use. This got me wondering about what kind of driver circuit these bulbs had, but when I took a look, it appears that they don't have any kind of driver or power supply circuit at all, and that the LED elements run directly from wall current!I have been seeing these "filament-style" LED bulbs quite a bit lately but have no idea how they are made or how they work. The light emitting elements look like relatively long strips; are they actually a bunch of LED junctions in a long strip? If not, any idea what they are?Here are a couple pictures of the bulb in question in case my description wasn't clear:Cheers,Rusty D.

author: Zero999
author_rank: Super Contributor
timestamp: July 23, 2017, 05:46:06 pm
content: I don't think they run directly off wall current. There will be a tiny capacitive dropper circuit integrated into the base. The filaments consist of many little LED dies in series, so the voltage can be relatively high and current low.

author: kalel
author_rank: Frequent Contributor
timestamp: July 23, 2017, 05:53:55 pm
content: There are a lot of tiny LEDs in there, running on relatively high voltage.There are all kinds of variants.Here is one:https://youtu.be/NffhdAz9pc4?t=559The circuit is in the base in this example.

author: boffin
author_rank: Unknown
timestamp: July 23, 2017, 05:56:11 pm
content: I suggest looking at some of Big Clive's videos on filament LED bulbs

author: kalel
author_rank: Frequent Contributor
timestamp: July 23, 2017, 06:31:27 pm
content: Quote from: boffin on July 23, 2017, 05:56:11 pmDefinitely.I linked one above, but there are multiple videos about it, and many about LEDs in general.

author: IanB
author_rank: Super Contributor
timestamp: July 23, 2017, 07:34:30 pm
content: Whether LED lamps flicker depends on the quality of the design. Some are better designed than others. I recently bought some of the same style of lamp and they seem fine to me, no observable flicker. They also claim to work with dimmers, though I haven't tried this.

author: Zero999
author_rank: Super Contributor
timestamp: July 23, 2017, 07:41:41 pm
content: Quote from: IanB on July 23, 2017, 07:34:30 pmI would have thought that LEDs which don't flicker, will have a larger base than those which do, as more room is required for the filter capacitor.

author: IanB
author_rank: Super Contributor
timestamp: July 23, 2017, 07:46:44 pm
content: Quote from: Hero999 on July 23, 2017, 07:41:41 pmSeems logical. My lamps have the standard base, not the miniature chandelier style. In fact, I am not sure how you can fit any electronics at all in a miniature base. Maybe the OP is right that there is nothing in there?For example, suppose you put about 30 LEDs in series with a small dropper resistor. You could put this string directly across the mains supply and they would self-rectify and need no additional circuitry. They would obviously flicker noticeably as they would only be lit up every half cycle. Maybe this is what the OP's lamp is doing?