Expected LED light bulb converter efficiency? (P_LEDs/P_mains) - Page 1
Forum section: electronics / beginners

author: RoGeorge
author_rank: Super Contributor
timestamp: May 06, 2022, 12:34:16 pm
content: For a mains light bulb marked, say 9W, how much of this power will be applied to the LEDs? Else said, what is the ballpark of the expected efficiency for a typical converter used in LED light bulbs?

author: RoGeorge
author_rank: Super Contributor
timestamp: May 08, 2022, 08:01:16 am
content: I don't want to open a good light bulb only for that. Anybody who knows the efficiency of a LED light bulb SMPS please, and can tell if it's more like 50%, or 90%? (unless it's asecret)

author: tunk
author_rank: Super Contributor
timestamp: May 08, 2022, 10:42:48 am
content: A few weeks ago I got some 4.8W bulbs. Opened one to see if they couldbe modified to run at a lower wattage. They measured 3.9W (260V, 15mA),so if you believe the 4.8W marking, they're around 80% efficient. Thinkmost LED bulbs don't use SMPSs.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 08, 2022, 11:27:05 am
content: Oh I didn't understand the OP question until I read Tunk's post. The OP wanted to know the ratio of the power applied to the LED over the power applied to the bulb as a ratio. So in fact an incandescent bulb this would be 100%. Well I wouldn't know the answer but I would believe they varied with bulb to bulb.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 08, 2022, 12:47:04 pm
content: Indeed, the question was not well put.My problem was like this: I have a dead 9W light bulb. The LEDs inside are fine, and I would like to power the LEDs alone, at DC, from a lab power supply. I guess 9W would be too much to apply (since those 9W includes the light bulb SMPS losses).How much power can be safely applied to those LEDs coming from a 9W light bulb?Considering about the same efficiencytunkfound, 80% (thank you), then the LEDs I have would support about 500mW each (9*80%=7.2W, divided by 14 LEDs is 514mW/LED).I've connected only 2 LEDs in parallel, and dialed up the current slowly while keeping an eye to the power. They start lighting at as low as 1mA.For 2 LEDs in parallel and 1.030W, the power supply measures 3.207V and 321mA (and 3.177V at 300mA).Rounded down, probably 0.5W LEDs, with nominal current of 150mA (and a voltage drop of about 3.15V).I was interested to find the nominal current of each LED, since I'm using them as loads to discharge/measure rechargeable AA/AAA batteries (with this method:https://www.eevblog.com/forum/projects/cc-cv-power-supply-as-a-contolled-load-for-batteries-(i-e-rigol-dp832)/msg4159222/#msg4159222)

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 08, 2022, 04:06:33 pm
content: 9W at what voltage? Knowing that you know the current. LED's are current devices so just supply the LED with the same current.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 08, 2022, 05:56:08 pm
content: If you want to connect some unknown LED's, then you can gradually increment their current.When LED's are over driven, their efficiency goes down, and the temperature rises disproportionately.Efficiency of small SMPS circuits is almost always between 85% and 98%.It depends a lot whether the manufacterer wants to make something decent, or something cheap.With very low voltages, the voltage drop over a diode reduces the efficiency dramatically, so synchronous converters are used to improve efficiency.But the best way is to do a bit of research, find datasheets of LED drivers and look at their properties.Efficency is almost always stated in the datasheet. sometimes with graphs for different input and output voltages and currents.

author: james_s
author_rank: Super Contributor
timestamp: May 08, 2022, 06:56:12 pm
content: LEDs are current driven, you just need to find how much current the LEDs are rated to handle and then drive them accordingly, letting the voltage go where it does. Gradually increasing the current while observing the brightness and temperature is a good option, as mentioned above, there is going to be a point where they stop looking much brighter and start getting hotter.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 08, 2022, 07:52:50 pm
content: Yes, I drive them by current, just that I don't have any datasheet, they are not marked (in the area cover by the brown wires it's written "2B7C 5730":To find the nominal current without a datasheet, I've used the nominal power of the light bulb derated at 80%:Quote from: RoGeorge on May 08, 2022, 12:47:04 pmDoh, while writing this post, googled the hidden text and found this:https://4.imimg.com/data4/TM/TE/MY-5541525/led-panel-light-housing.pdffrom where it seems the "5730" might be the type of LED.Googled "5730 smd led" and found the datasheet:http://led-obzor.com/led/led-smd-5630-5730https://www.micros.com.pl/mediaserver/info-olb.5730.2700k.pdfThank you all, solved!

author: SmallCog
author_rank: Frequent Contributor
timestamp: May 10, 2022, 03:07:09 am
content: You may need to pop one open unfortunatelyThey may have a little switchmode in them but are more likley a capacitive dropper or linear regBigClive has a bunch of videos on this topic where he pulls apart various lights

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2022, 04:52:33 pm
content: The LEDs in that picture look a bit like Osram Duris series, a datasheet for those will probably get you in the right ballpark for current.