Mains harmonic emissions for dimmable offline LED drivers.

[treez]

Hi,
As you know, its not difficult to design and build an offline SMPS LED driver that can run at 235W output, and 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?
How do the regulations deal with dimmable LED drivers. At what power level are mains harmonics tested?

 

[volker@muehlhaus]

I looked at LED driver EMC regulations a while ago. From what I remember, you need to test the worst case that is likely in real operation.

https://ec.europa.eu/docsroom/documents/33601

 

[FvM]

They may e newer or more specific test specifications for dimmable LED lamps. The best fitting specification in IEC 61000-2-3:2009 says under C.5.3 Luminaires:

If a luminaire has a built-in dimming device, the harmonic currents shall be measured at the maximum load of the lamps as specified by the manufacturer. The setting of the dimming device is varied in five equidistant steps between the minimum and the maximum power in order to obtain comprehensive results.

My general assumption is that lighting products, except for incandescent lamps with dimmer, belong to the class C.

 

[treez]

Thanks for your quote. From the way that is worded, it does look to me that the mains harmonics are only to be tested at the maximum load. It talks about five equal dimming steps from min to max, but doesnt say that mains harmonics must pass at any of these levels...

......It all makes sense, because it is going to be very challenging to pass mains harmonics at 25w, with an offline SMPS LED driver that is designed to supply a 235W maximum load. In fact, I would say that this is not even a practicable proposition. Would you agree? –The 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.
..surely you agree?

I once worked at a lighting company…and we used to design our offline SMPS lighting product for a higher power than it would ever be sold for (it would be used at multiple different, lower powers, depending on the particular customer). Our boss, kind of smilingly referred to it as a “cheat”, when we asked him why we were designing it for the irrelevant higher power, but of course, we weren’t actually breaking any regulations in reality.

 

[volker@muehlhaus]

treez, please let me know what company you work for, so that I can stay away from products that you designed. You always try to interpret specs and regulations to your liking.

 

[treez]

Thanks, I would love to be able to afford these specs so i can read exactly what is said.
The thing is, there is a question here which may remain unanswered, and that is the following....

It is going to be very challenging to pass mains harmonics at 25w, with an offline SMPS LED driver that is designed to supply a 235W maximum load. In fact, I would say that this is not even a practicable proposition. Would you agree? –The 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.
..surely you agree?

But i suspect the regulations dont even cover the mains harmonics for 25w operation of a 235w offline SMPS LED driver.
The regulations also dont completely cover the situation with TO220 FETs, as the following thread shows....
https://www.edaboard.com/showthread...learance-between-drain-and-source-pads-on-PCB

Also, there is no coverage in the regs for whether or not a PFC stage is needed for 300W+ Class D audio amplifiers which , in their actual useage, have an average power less than 75W, even though their peak power is at 300W+.

 

[volker@muehlhaus]

Have you read my link above?

Section 4.3 EMC Assessment
4.3.1 General Concept

The EMC assessment needs to take into account all normal intended operating conditions of the apparatus. In cases where the apparatus can take different configurations, the electromagnetic compatibility assessment must confirm that the apparatus meets the essential requirements, “in all possible configurations identified by the manufacturer as representative of its intended use”.

 

[treez]

Thanks Volker…

The EMC assessment needs to take into account all normal intended operating conditions of the apparatus. In cases where the apparatus can take different configurations, the electromagnetic compatibility assessment must confirm that the apparatus meets the essential requirements, “in all possible configurations identified by the manufacturer as representative of its intended use”.

..i hate to say it, but that is open to interpretation, and also, it says that it only concerns those conditions identified by the “manufacturer”, and not by the approvals body.

....Supposing that the manufacturer sells the lamp as being for use from 235W to 50W, and knows that it fails mains harmonics at 25w….but still gives the facility for the customer to be able to dim it to 25w…what then?

Also, I would put it to all, that designing a dimmable offline SMPS LED driver which can pass mains harmonics at all power levels from 235W down to 25w, is not economically feasible...would you agree?

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The following offline 600W LED lamp is dimmable down to zero Watts.
I think we can be virtually certain that it doesnt pass mains harmonics levels at 25w power.
-But "operation at 25w power" is not actually stated in its datasheet

https://www.alibaba.com/product-det....normalList.13.24011c94lLiwtl&s=p&bypass=true

...so its perfectly legal , and sells in high numbers throughout the EU. Its not illegal to operate it at 25w.

Perhaps if it was illegal to operate it at 25w (because it fails mains harmonic emission levels at 25W) , then the customer could simply dim it up to 50w, where it may just pass mains harmonics levels….but that would kind of be ironic wouldn’t it?...i mean, a waste of 25w just to operate at a level which passes mains harmonics. –What benefit is that to anyone?

 

[treez]

Hi
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.

 

[Easy peasy]

The aim should be to make it as good as possible at the lower powers, testing other makers products is a good place to learn, below 30W there are, I think different standards for lighting products - so you can argue you meet these - however - it is possible to draw low harmonics from 235W to 25W if you have a good topology and filtering - a dual interleaved flyback could do this quite easily for example - kind regards

 

[treez]

below 30W there are, I think different standards for lighting products

Thanks, but we are sure its Table 2, page 7 (class C ) standard for 25W upwards for lighting supplies...
**broken link removed**

Interestingly, a Dual interleaved offline Flyback converter would need a custom made controller (eg micro etc), since there are no off-the-shelf controllers for offline dual interleaved flyback.

 

[Easy peasy]

FAN9611 fits the bill for controller I think ...

 

[treez]

OK thanks, ill look into adapting it for opto-isolated feedback.

 

[treez]

The aim should be to make it as good as possible at the lower powers, testing other makers products is a good place to learn, below 30W there are, I think different standards for lighting products - so you can argue you meet these - however - it is possible to draw low harmonics from 235W to 25W if you have a good topology and filtering - a dual interleaved flyback could do this quite easily for example - kind regards

As discussed, the Class C regulations require conformance all the way down to 25W. However, as I have remarked, its not economically feasible to produce an offline SMPS LED driver of power >100W that can pass mains harmonics at 100W and at 25W.

Even if one believes that it is possible to produce an offline SMPS LED driver which could pass mains harmonics at 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.

 

[Easy peasy]

agreed - large filter caps add phase shift at light loads - the key is an emc filter with more L than C ...

I note in the spec that quite a bit of 3rd is allowed and others at 25W, if you label your luminaire to say it only operates from 50W to 250W - this would meet spec - need to set Pmin in hardware though ...

 

[treez]

if you label your luminaire to say it only operates from 50W to 250W - this would meet spec - need to set Pmin in hardware though ...

Thanks i see what you mean and agree.
This does appear to be a mistake in the regulations though.......i mean, the customer may only need 25W at a certain time, but would have to use 50W...wasting energy.
I dont think that the regulations have caught up with dimmable LED drivers yet.

I'd like to find an offtheshelf LED driver that was hardware limited in min power to say 50W, and take it to Greta Thunberg and co...they'd have a field day with it.

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the key is an emc filter with more L than C ...

Thanks, agreed, of course, as you know, this needs care, to avoid an input filter with too-high output impedance, which would cause input filter instability.