Mains harmonic emissions from offline dimmable SMPS LED drivers - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: November 16, 2019, 08:43:29 pm
content: As you know, its not difficult to design and build an offline SMPS LED driver that can run at 235W output, and that can also be dimmable down to 25W output. (eg, a Boost PFC followed by a 2 transistor forward converter).However, its far more challenging to make it able to pass mains harmonic emissions at 235W, and also at 25W. This is because the EMC filter necessary to make it pass conducted emissions at 235W, will generally mean that the mains harmonics at 25W are not a pass. (the input stage filter capacitors will generally be too big to allow a mains harmonic pass at 25W)Would you agree with this?

author: ocset
author_rank: Super Contributor
timestamp: November 17, 2019, 07:45:02 pm
content: Sorry to harp on...The attached LTspice simulations show a 97W PFC’d Flyback LED driver which passes mains harmonics at 97W…but when the dimmed down version at 29W is simulated, we see it fails on the 3rd harmonic.Do you agree that it is not economically feasiable to make a 235W Offline SMPS LED driver which passes mains harmonics at 235W, and also passes mains harmonics when dimmed down to 25w operation?The excel file where the harmonics are calculated is also attached.

author: f4eru
author_rank: Super Contributor
timestamp: November 18, 2019, 05:17:44 pm
content: could you please put the attachements in readable format ?

author: ocset
author_rank: Super Contributor
timestamp: November 18, 2019, 08:05:16 pm
content: The .asc attachements are in LTspice simualtion format...LTspice is a free simulator that can be downloaded from the analog.com website.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 19, 2019, 12:18:40 am
content: Quote from: f4eru on November 18, 2019, 05:17:44 pmI agree, please post PNGs or PDFs along with the raw schematic files.

author: temperance
author_rank: Super Contributor
timestamp: November 19, 2019, 09:11:14 am
content: I'm not a frequent visitor if this board but I rather quickly spotted the following pattern:-You have a habit of posting one engineering difficulty after an other on this board and expect people to solve your problems.-You're own input on you're own topics is below zero and you're even absent in your own topics.-You even expect people to serve you boiler plate solutions.-You like people to search the web for you even for an off the shelf switching power supply which is nothing special.It could be that you:1. are a clueless engineering manager.2. the coffee machine expert who wants to brag and sound great while what you have to say is stolen from other people.3. two and three combined. A pain in the ass to just everyone in the engineering department.You probably lack the engineering spirit to solve real problems.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 19, 2019, 12:23:58 pm
content: Quote from: temperance on November 19, 2019, 09:11:14 amIn addition to this forum the same question was asked on other forums:https://www.electro-tech-online.com/threads/passing-mains-harmonic-emissions-with-dimmable-offline-led-driver.157866/andhttps://www.edaboard.com/showthread.php?387657-Mains-harmonic-emissions-for-dimmable-offline-LED-drivers&p=1666587To get to the topic at hand:Here is the LTspice schematic that was shared by Treez:The difference between the two is the voltage source V2 it is 0.5V on the 97W version and 0.17V on 29W version.There is a conflict on the model between the transformer note NS/NP = 0.329 and the inductance ration 270uH : 100uH270uH: 100uH is Ns/Np =0.608This is because inductance is proportional to N2.What is the correct turns ratio?In addition the model presented differs from the manufacturers reference designs. All the reference designs have electrolytic capacitors in the output circuit, C6. This provides energy storage, key to the operation of a PFC.The.tran 0 20m 0 startupruns the simulation for a single line cycle, at 50 Hz, and includes some start-up transients.Change the .tran directive to:.tran 0 100m 40m startupThis will run the simulation for a total of 5 line cycles. The first two cycles are discarded.If you do this you will finds that the third harmonic, 150Hz, is reduced.Regards,Jay_Diddy_B

author: ocset
author_rank: Super Contributor
timestamp: November 19, 2019, 08:45:30 pm
content: Thanks, i would have to be honest and say the simulations were just provided as a kind of general reference, rather than being the central points of the question......its possible to run them, and fiddle with the power levels, and note the significantly worsening of harmonics when at the lower power of 25W.Thankyou for pointing out that i didnt run the sims long enough....in fact, they take ages to run on my PC, and also the general point i am making is just that its not economically feasible to make a offline SMPS LED driver which passes mains harmonics at maximum power, and also at 25w, if the maximum power is > around 120W or so.Even if one believes that it is possible to produce an offline SMPS LED driver which could pass mains harmonics at let's say 100W and 25W…..we all have to admit, that there is a certain maximum power level, whatever it may be, where it can pass mains harmonics at that maximum power level, but not at 25W….for you, this “maximum power level” may be 100W, 200W or 300W, or more…..but we all admit that there is a hard limit somewhere. I very much doubt that many people would expect it to be economically feasible to pass mains harmonics at 250W and at 25W……not with any economically feasible topology.–The conducted EMC filter capacitors would simply be too large and would distort the waveform too much at 25W….resulting in mains harmonic failure at the 25W level.If you say its possible to do it at 250W and 25W…then where is your limit?...i can’’t be much higher than 250W.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 19, 2019, 09:00:55 pm
content: Quote from: treez on November 19, 2019, 08:45:30 pmQuoteQuoteQuoteThe incessant use of equivocating language is proof enough that the poster does not believe the statements they are making. Or believe that others agree. (Which begs the question, why ask?)Perhaps they should just try harder.Quote from: temperance on November 19, 2019, 09:11:14 amQuote from: Jay_Diddy_B on November 19, 2019, 12:23:58 pmIndeed, OP's history goes back many years, over a decade from what I can recall; they were on the DutchForce Electronics Forum (now defunct) in its heyday. I'm not aware they ever got into newsgroups.Tim

author: ocset
author_rank: Super Contributor
timestamp: November 20, 2019, 08:26:05 pm
content: QuoteThanks, though i confess i have solved some nice problems for others on this great forum...one guy i gave him a superb circuit which reduced overhsoot dramatically....for another guy i gave a superb dual boost converter for his nixie tube supply...which reminds me, i need to find time to get back to see how he got on...i gave him a pretty full schem and sim, plus explanation.....plus my free SMPS course...found here...somewhere...QuoteThanks, i know what you mean......the big electrolytic output capacitors mean you dont get 100Hz flicker on the output of a PFC'd flyback led driver...of course, as you know, the big output capacitance is definetely not needed to achieve PFC itself.

author: temperance
author_rank: Super Contributor
timestamp: January 17, 2020, 08:45:36 pm
content: @ treezI just looked at your google drive. Very impressive.I want to send you my apology for calling you an incompetent engineer and some other things. After reading some of your posts I started thinking you're the kind of person who can't solve his own problems while you are actually sharing your insight into the problems you encounter.

author: TheDood
author_rank: Regular Contributor
timestamp: January 30, 2020, 12:47:53 am
content: Quote from: treez on November 20, 2019, 08:26:05 pmThanks Treez, I'm going to check out your SMPS course. I'm trying to build a highly efficient LED driver myself. Glad to hear it's easy lol I've been trying to develop a PFC solution without a premade controller IC.I was thinking a PFC stage followed by an inverter followed by a couple capacitive power supplies (2 LED arrays) being fed by the PFC cap. I could control current by the inverter switching Hz. Feel free to drop any knowledge or if I'm barking up the wrong tree(z) lol

author: f4eru
author_rank: Super Contributor
timestamp: February 02, 2020, 03:45:22 pm
content: Which norms require you to pass harmonics at 25 W ?As far a I know, it´s only when > ~70W or so....