LED Three Way Lightbulb Innards - Page 1
Forum section: electronics / projects

author: Infrared_Fred
author_rank: Regular Contributor
timestamp: August 09, 2022, 08:41:30 pm
content: Does anyone know how the driver works in a three way LED bulb,esp. does anyone happen to know of a schematic for one? I tried doing a Google search for "three way led bulb schematic" and "LED three way bulb how it works", but neither got any useful results. The sources tended o explain how an incandescent 3-way bulb works, but I couldn't find any desciption of how the LED driver works for those bulbs. I would love take one apart, except my curiousity is reigned in upon by my budget, and I don't have any dead ones yet.Thanks for the help!

author: Faringdon
author_rank: Super Contributor
timestamp: August 09, 2022, 09:52:16 pm
content: Here is one for you in the free LTspice sim package.Just adjust the reference voltage v4 to get the different light level......ive shown it here dimming down every 10ms.You coudl just have a switch to input the required ref voltage.

author: thm_w
author_rank: Super Contributor
timestamp: August 09, 2022, 10:20:07 pm
content: https://en.wikipedia.org/wiki/3-way_lampThey might use a microcontroller that senses which inputs are connected. Or two completely separate LED drivers and circuitry (seems unlikely, cost would be higher).Never heard of these things before.

author: james_s
author_rank: Super Contributor
timestamp: August 09, 2022, 10:42:31 pm
content: I have a couple but I've never opened one up to see how it works. My bet is they have some clever and very cheap analog circuit that sets the current of the LED driver depending on which of the two live terminals are active. Just take power from either one using diodes and then all you have to do is sense which one(s) are live.

author: themadhippy
author_rank: Super Contributor
timestamp: August 09, 2022, 11:35:15 pm
content: reading the wiki link i can see some confusion waiting to happen in electrical suppliers over in the land were they call 2 way lighting 3 way.

author: james_s
author_rank: Super Contributor
timestamp: August 10, 2022, 03:28:15 am
content: Quote from: themadhippy on August 09, 2022, 11:35:15 pmI doubt it. "3 way" switches and 3 way bulbs have been around for many decades, they are completely different things but it never seemed to cause confusion. A 3 way switch is a switch that has 3 terminals that allows a light to be controlled from two (or more by adding one or more 4 way switches between them) locations. A 3 way bulb is a bulb that has three brightness settings, by containing a pair of filaments of different wattages and a special socket with a sequential switch. Both have been in common use at least as far back as the 1930s and both are still widely available.

author: themadhippy
author_rank: Super Contributor
timestamp: August 10, 2022, 01:40:46 pm
content: Quoteanother example of confusion,to me a 4 way switch can go to 1 of 4 positions,when in fact it only goes to 2 positions,not saying the uk calling them intermediate switches makes things any clearer,but at least theres less chance of confusion.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 10, 2022, 01:51:49 pm
content: Quote from: james_s on August 10, 2022, 03:28:15 amHasn't the 3 way bulb became largely obsolete since the introduction of dimmers?

author: TimFox
author_rank: Super Contributor
timestamp: August 10, 2022, 02:19:55 pm
content: Most traditional floor lamps in the US are wired for "three-way" bulbs, with two internal filaments. For example, a 100 W and a 50 W filament, to allow 50, 100, and 150 W settings.The "four-way" switch has been standard nomenclature in the US (for a DPDT switch wired as a reversing switch) for my entire lifetime, and I'm old.A rotary switch that has four positions is the "4T" (four throw) in SP4T (for example).

author: james_s
author_rank: Super Contributor
timestamp: August 10, 2022, 09:01:31 pm
content: Quote from: themadhippy on August 10, 2022, 01:40:46 pmI'm not really sure it matters, a 4 way switch has four terminals, not four positions. Intermediate switch isn't any more self explanatory, it's just a different name and it makes sense to you because that's what you've always called them. They could be called anything and you'd learn what the name was. To most people a 3 way switch or a 4 way switch or a standard single switch is just a switch, they don't know or care how it works internally, they just want to light to turn on or off when they flip it and it would never occur to them that there are different types of switch. The technical details only matter to electricians and knowledgeable DIY types.

author: james_s
author_rank: Super Contributor
timestamp: August 10, 2022, 09:04:05 pm
content: Quote from: TimFox on August 10, 2022, 02:19:55 pmMost medium and larger table lamps as well, it is virtually universal. I have several table and floor lamps in my house and I think every one of them has a 3-way socket, although only the big antique mogul base floor lamp has a 100-200-300W 3-way bulb in it, the rest are all LED. Lamps with dimmers built in have been available since the 80s but they have never been common.

author: themadhippy
author_rank: Super Contributor
timestamp: August 10, 2022, 09:14:42 pm
content: Quotemaybe to you,but to me it would have 5 terminals,common and 4 outputs.If your naming switches on the number of terminals its has, what about a double pole switch?thats also got 4 terminals

author: TimFox
author_rank: Super Contributor
timestamp: August 10, 2022, 09:19:51 pm
content: Standard nomenclature in electronics for (single-or-multiple poles) with (multiple positions) includes:SPST DPST 4PSTSPDT DPDT .... 4PDT... ... ...SP4T DP4T 4P4T... ... ...Where it is easy to see how many moving (P) and fixed (T) contacts are involved.

author: james_s
author_rank: Super Contributor
timestamp: August 11, 2022, 01:27:27 am
content: Quote from: themadhippy on August 10, 2022, 09:14:42 pmWell we've established before, we both speak "English" but it's not the same language. There are all sorts of things with different names, and words that are the same but have different meanings. That's before you even get to the local dialects and colloquial terms and slang.And responding to Tim, yes I think terms like SPDT are superior in that they are self explanatory once you learn a couple of very simple rules, but tell an electrician you want a SPST switch and he's likely to give you a blank stare.

author: TimFox
author_rank: Super Contributor
timestamp: August 11, 2022, 03:45:00 am
content: That's why I said "in electronics".When talking to electricians, I say three-way or four-way switch and we understand each other.