Burst mode SMPS will fail Conducted EMC? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: May 09, 2023, 01:57:07 pm
content: Hi,We are doing a burst mode power supply, (2 tran Fwd with BCM Boost PFC) load is full to no load transients and vice versa, all the time.Around 10ms ON, 10ms OFF...repeatedly100-265vac, 400w peak, 200w average, 37vout.Why does the contractor say it will fail Conducted EMC?The burst frequencies are below 150kHz..and the EN55022 regs dont apply as strictly below 150khz.

author: Gyro
author_rank: Super Contributor
timestamp: May 09, 2023, 08:15:29 pm
content: Quote from: Faringdon on May 09, 2023, 01:57:07 pmWhy don't you ask them?

author: jonpaul
author_rank: Super Contributor
timestamp: May 14, 2023, 09:29:52 pm
content: will fail flicker regs

author: Faringdon
author_rank: Super Contributor
timestamp: May 15, 2023, 06:10:51 am
content: Thanks, do you know what EN number that is?...then i will purchase 24hrs viewing of it on EVS.EEIf it would fail flicker regs...then couldnt we just sense the load current, and when constant for >4 seconds (that would only happen during conducted EMC test) ......then we would just make it transistion to frequency compensated mode...this is cheating the standards but makes no difference in real terms...at the end of the day, whether you have a frequency compensated SMPS, or a burst mode SMPS, ...if your load involves nothign other than full load transient switching, then both versions of smps will give the same "flicker".Where eg mains harmonics are concerned, you can find documents (as below) which tell you what exactly it is....but flicker is different, its impossible to find out what kind of pulsed current draw would make you fail flicker.https://www.emcstandards.co.uk/files/61000-3-2_mains_harmonics.pdf

author: jonpaul
author_rank: Super Contributor
timestamp: May 15, 2023, 06:20:55 am
content: FTTS...Kindly suggest that you finally Research and learn about flicker, compliance and SMPS design. Many fine books and seminars, eg at IEEE PESC, PCIM, Nuremberg, etc.Pleasee see my detailed y invoice for acumulated time on your questions since last years, EU100K.Today special disacount! EU 85K if you pay this week.Master Card, Visa and AmEx cards gladly accepted...(:-:)Jon

author: Faringdon
author_rank: Super Contributor
timestamp: May 15, 2023, 10:38:26 am
content: Thanks, Flicker appears to be covered by EN61000-3 and EN61000-4-15.Does anyone know of any free summaries of these standards.?Also, its one thing saying that a PSU introduces flicker because its in burst mode...but what if the load of a PSU is always "pulsey" anyway, and introduces flicker anyway...which would be there even if a "smooth" non-burst-mode SMPS had been used (ie , a frequency compensated SMPS had been used).Do the standards address this situation?

author: f4eru
author_rank: Super Contributor
timestamp: May 15, 2023, 08:41:32 pm
content: The usual procedure is :1) Buy the norm.2) Read the norm3) understand the norm4) "click5) ....6) design stuff7) profit.

author: jonpaul
author_rank: Super Contributor
timestamp: May 16, 2023, 06:13:24 am
content: FTSS: Why bother with burst mode....entire thread seems bizzare...Burst mode is only used for sleep/power miser idle in battery powered portable ...No benefits in off line SMPSj

author: Faringdon
author_rank: Super Contributor
timestamp: May 16, 2023, 05:52:59 pm
content: Though a story is becoming...because its amazing how a massive number of Power electronics company staff think that a burst mode SMPS is worse at EMC , than a standard frequency compensated SMPS.....which if course, is totally not true....neither does it fail flicker.I once worked at a co, where they had a 600W UV lamp, which was on a gantry going back and forth, every time it hit the gantry end, the 600W was suddenly turned off, then suddenly turned back on again some 2 seconds later......the full load transient made the output go up to >60V.....and it eventually blew up the control PCB.......they were asked why they didnt use a Burst mode SMPS....which would have alleviated the problem....they said , because Burst Mode would fail EMC....which of course, is nonsense...they are pretty much just the same at EMC as a standard frequency compensated SMPS.(ayk, a Burst mode smps, which has a hysteretic comparator at output for regulation.....has a certain fixed peak current setting.....if you incrementally increase its load...you will eventually get to a stage where its output drops a little , and it goes into continuous mode..not bursting.............if you use it for a power level which is just a bit lower than dropout, then it is in burst mode, but its peak current level is pretty well the same as what you'd get with a frequency compensated SMPS.)Take the following nonsense written about Burst mode...https://www.electronicproducts.com/burst-mode-operation-a-double-edged-sword-for-power-supply-manufacturers-users/..They say the filter woudlnt work....burst mode switching in bursts at a certain frequency will give no problem to a standard emc filter.

author: Gyro
author_rank: Super Contributor
timestamp: May 16, 2023, 07:00:06 pm
content: Ahh, Treez: The lighting years. Nostalgic indeed.

author: TimNJ
author_rank: Super Contributor
timestamp: May 16, 2023, 07:54:58 pm
content: Quote from: jonpaul on May 16, 2023, 06:13:24 amThere are mandated EU and DoE requirements on no-load standby power consumption for external power adapters. Open-frame types have no such requirement that I am aware of. Some market sectors are exempt (e.g. medical). External power adapters also need to meet certain average efficiencies based on their nameplate power rating. Certain topologies may suffer a lot at light load (25%), so burst mode is really needed for this condition. And EU and DoE have been tossing around setting minimum efficiency at 10% nameplate power for a while now, though not likely to go into effect (soon).

author: Faringdon
author_rank: Super Contributor
timestamp: May 17, 2023, 05:46:41 am
content: Thanks, i am speakign of burst mode for the whole load range, zero to 100%...which , as you know, is fine.....we will see a massive resurgence of burst mode , specially when loads are transient in nature.

author: Faringdon
author_rank: Super Contributor
timestamp: May 17, 2023, 07:06:53 pm
content: Also..Also, an offline Burst mode PSU can avoid serious output voltage overshoot and undervoltage following transients.....and do so with extremely minimal output capacitance...not so for a frequency compensated SMPS with an opto in the feedback path.....Burst mode 2 tran forward , 400W..and you dont even need output 'lytics...low value film cap will do.

author: langwadt
author_rank: Super Contributor
timestamp: May 17, 2023, 08:41:33 pm
content: Quote from: f4eru on May 15, 2023, 08:41:32 pmyou usually have to repeat 1 and 2 ad infinitum, because each norm just refers to another norm

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 18, 2023, 12:10:59 pm
content: Quote from: Faringdon on May 09, 2023, 01:57:07 pmIt's unclear whether "burst mode" refers to a behavior of the PSU controller (which manifests under light load conditions) or a behavior of the load on the PSU. These are completely different things.Also, I don't think it's useful to implement burst mode control for a PFC front end, at least not in a conventional way. Burst mode is common in the DC-DC stage though. I don't see any reason to expect burst mode control to have worse EMC outcomes. A pulsed load, on the other hand, may be an issue for some tests like flicker, as others have stated. But if you're just designing a PSU, such testing would be up to the end user, I assume?

author: jonpaul
author_rank: Super Contributor
timestamp: May 18, 2023, 03:37:33 pm
content: Many solutions exist for flicker and stby power compliance.Burst mode is just one.Jon

author: Faringdon
author_rank: Super Contributor
timestamp: May 18, 2023, 05:29:29 pm
content: QuoteThanks, totally agree.And of course with Burst mode...for especially offline SMPS..you get fantastic transient response, with very very little output capacitance...and the capacitance you have doesnt need to be electrolytic....your undershoot and overshoot following full load transient switching is tightly controlled.