Electronic 12V transformer for GU5.3 MR16 LED bulbs - Page 1
Forum section: electronics / projects

author: thexeno
author_rank: Regular Contributor
timestamp: September 03, 2019, 09:50:37 am
content: Hi,I have an electric setup in the house with toroidal AC trasnformers (230V to 12V) to lilght up the 12V MR16 lights. I switched from 35W or 50W halogen to 7W LED type.But I read on the blister the suggestion, which seems to me, to use an electronic transformer type. What does it mean? they seem to work ok with the conventional one.Here the pictures of the blister attached.

author: thexeno
author_rank: Regular Contributor
timestamp: September 03, 2019, 09:53:06 am
content: This is the other picture.

author: Zero999
author_rank: Super Contributor
timestamp: September 03, 2019, 10:37:15 am
content: There's nothing on the photographs you've posted recommending an electronic transformer, in English.I think it will work with the existing toroidal transformer. Just replace the bulbs.

author: thexeno
author_rank: Regular Contributor
timestamp: September 03, 2019, 11:32:20 am
content: Quote from: Zero999 on September 03, 2019, 10:37:15 amSorry I have not highlighted the picture.It shows on the first "AC electronic", and on the second check the diagram on the left of the CE mark.

author: Zero999
author_rank: Super Contributor
timestamp: September 03, 2019, 04:17:54 pm
content: Quote from: thexeno on September 03, 2019, 11:32:20 amWhy do you think that means use an electronic transformer?The phrase "AC electronic" doesn't mean anything in English, so I just assumed it's a foreign language and means it's designed for AC electricity.In my experience, LED lamps designed to replace halogens are more likely to be comparable with a mains frequency transformer, than electronic one. They're normally designed to work with electronic transformers, but they don't always work perfectly. I've had issues with flicker and intermittent operation with a halogen replacement LED lamp and an electronic transformer before. It was resolved by replacing the transformer with on of the same brand as those used in other fittings which were already powering LEDs properly. I did consider replacing all of the electronic transformers in that installation, with a single mains frequency one, but decided it wasn't worth it.

author: ledtester
author_rank: Super Contributor
timestamp: September 03, 2019, 04:59:27 pm
content: Quote from: Zero999 on September 03, 2019, 04:17:54 pmWhat are they trying to say with these pictograms?

author: Zero999
author_rank: Super Contributor
timestamp: September 03, 2019, 08:28:57 pm
content: Quote from: ledtester on September 03, 2019, 04:59:27 pmWell spotted. Then it's clearly designed for electronic transformers only, which is odd, but why the hell didn't they say so in plain English, rather than a dumb graphic, which most people won't notice?I dare say the average person won't even know whether the fitting has an electronic or mains frequency transformer. It's retarded. I wouldn't bother replacing the transformer. I'd return those LED bulbs and buy some which will work from a mains frequency transformer.

author: thexeno
author_rank: Regular Contributor
timestamp: September 07, 2019, 05:24:59 pm
content: Ok, I thought the same. Sorry, I should have put arrows in the picture.But then, seems to work without visible issues.Could be that might get damage over time? Now I have them for 3 months already... It does not seem to overheat, but I don't have a reference to be sure for that.My engineer side is telling me to make an age test and see if they survive on the 50Hz line over time

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 07, 2019, 05:45:52 pm
content: Might be because they might flicker. I suggest testing one on a bench PSU to see if it works on DC, and if so, just replacing the transformers with 12V PSUs.

author: Zero999
author_rank: Super Contributor
timestamp: September 07, 2019, 06:35:18 pm
content: Quote from: thexeno on September 07, 2019, 05:24:59 pmIf they're working without any issues then leave them alone. They won't damage the transformer and if they stop working, they're easy to replace.

author: thexeno
author_rank: Regular Contributor
timestamp: September 14, 2019, 09:23:46 am
content: Quote from: Zero999 on September 07, 2019, 06:35:18 pmI was a bit worried that they might become a EM power transmitter in terms of EMI (the regulator working in different modes with 50Hz, or the like, wildly switching to keep track of the slow, high swing changing voltage). But I have no clue to qualitatively check that....

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 14, 2019, 09:48:43 am
content: Also anormalhalogen transformer is rated to 11.something Volt under the rated load. So if you replace the 50W bulb by 7W LED the voltage will be higher. And if you have multiple bulbs it get even worse. Depending on the transformer it can exceed the 12V. That's probably the reason of the short LED lifetime some people face. Switching PSUs shouldn't suffer this problem as they are regulated.By the way that is also the reason why it is a good idea to replace a burnt halogen bulb quickly if multiple bulbs are connected in parallel. The increased voltage will shorten the lifetime of the others.

author: Zero999
author_rank: Super Contributor
timestamp: September 14, 2019, 09:11:58 pm
content: I would have thought there would be less EMI when powered from 50Hz, than the 50kHz. It's generally recommended to keep cable runs as short as possible with electronic transformers, to minimise EMI. Quire often, each lamp will have its own transformer, so the cables can be very short. Conventional transformers are less of a problem: just make the cable thick enough, do the voltage drop isn't significant, with the maximum length being determined by the wire gauge which will fit in the terminals.If the LED lamps are properly designed, they should work over a reasonably wide voltage range, so the slightly higher voltage from a lightly loaded transformer won't be a problem. It should have a switched mode power supply, which will deliver the same current to the LED dies, over a reasonably wide supply voltage range.Electronic transformers aren't regulated either. They typically consist of a Royer oscillator driving a high frequency transformer, with no feedback. It's possible electronic transformers offer better regulation, than conventional transformers, because they have lower copper losses, but they also have additional losses in the rectifier and transistors. Regulation specifications for conventional transformers are easy to find, but I haven't found any for electronic transformers, so it's not possible to compare, unless one has the time and resources to do the experiments. Here's an SG application note on electronic transformers.https://www.st.com/content/ccc/resource/technical/document/application_note/e5/88/46/11/35/8c/4a/bf/CD00003902.pdf/files/CD00003902.pdf/jcr:content/translations/en.CD00003902.pdfIt's actually more difficult to design an LED lamp to be compatible with an electronic transformer, compared to a conventional one. Electronic transformers typically require a minimum load current, which is much greater than an LED lamp, so various tricks need to be employed to make it work. This is why I'm surprised this LED is recommended for use with electronic transformers only. Here's a brief presentation I've found on designing LED lamps to work off electronic transformers.https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&cad=rja&uact=8&ved=2ahUKEwiG5-fHmNHkAhXUasAKHcnGC44QFjAKegQIAhAC&url=http%3A%2F%2Fwww.deyisupport.com%2Fcfs-file.ashx%2F__key%2Fcommunityserver-discussions-components-files%2F24%2F7711.Transformer-application.pdf&usg=AOvVaw1O71tqHvjAr0ZlgfiOK-9nI suspect people have problems with short LED lifetimes because they have bought cheap, crappy LEDs. It may be even more of a problem if they're run off an electronic transformer, as the slow rectifier diodes in cheap LED designed for 50Hz, will get much hotter at 50kHz, assuming they use enough to fulfil the minimum load requirement of the transformer, so it actually works.

author: thexeno
author_rank: Regular Contributor
timestamp: December 16, 2019, 02:15:44 pm
content: As additional thought on my original post, I read thisAN022, paragraph 8.Which makes me think that my LED lamp was showing the capability to work with electronic transformer, while some other LED lamps do not. AFAIK, the conventional toroidal transformer should always work.If the assumption is correct, this makes the LED lamp an higher quality than other LEDs ones, not a worse one as initially thought. Despite the package documentation might not be at the same quality level, as I am still making assumptions. But I thought it could be an interesting read.

author: Zero999
author_rank: Super Contributor
timestamp: December 16, 2019, 06:23:49 pm
content: Quote from: thexeno on December 16, 2019, 02:15:44 pmI agree, it should have no problems working off an ordinary iron core transformer. I suspect it will also work of a wide range of AC or DC voltage.