Why are low power, offline LED lightbulbs power factor corrected?

[Flyback]

Regarding offline SMPS's for driving LED lightbulbs of 7W+, virtually every single semiconductor company offering (as linked below) is using power factor correction, even though PFC is officially not required below 25W.

Why is this?

Is it because non power factor corrected circuits have large-ish electrolytic caps after the mains rectifier bridge which may get damaged by overvoltage spikes when/if the bulb is accidentally connected to a triac dimmer? (ie, overvoltage spikes due to input filter resonance).
Or is it because they are genuinely concerned about losses in the electricity supply system?
Or is it because mains voltage spikes might damage a primary side electrolytic capacitor, more than say a film capacitor?
Or is it because PFC operation means an overall lower voltage across the switching fet, which means less switching losses?
Or is it because operation with dimmers requires the primary dc bus voltage to fall quickly as the phase cut dimmer turns off?
Or is it because they don't want electrolytics at the primary dc bus, because they eventually get worn out by inrush current every time the led bulb is turned on?

 

[jpanhalt]

I think this editorial makes a good argument why PFC is included in the smaller supplies. Namely, as LED lighting becomes more common, the cumulative effect of non-PFC supplies will be significant. According to the author, it is part of the "green" initiative: **broken link removed**

This TI datasheet describes some additional rationale: https://www.ti.com/lit/ds/symlink/lm3450.pdf

John

 

[Flyback]

Thanks, your first article was very informative...of course, considering that article, which emphasises the importance of PFC, the following thread states how PFC is not so important..
https://www.electro-tech-online.com/threads/worldwide-lighting-made-20-more-efficienct.135162/
Also, a PFC'd flyback LED driver will inevitably have a higher RMS fet current than one not using pfc. -so it'll be slightly more inefficient.
Of course, estimating the actual losses in the supply system that would result by *not* implementing PFC in LED lightbulbs is something that would be severely difficult to calculate.
With CFLs for example, if they are to be PFC'd, then typically it requires a front end boost PFC stage, which means the overall CFL bulb is more inefficient. It would be nice to know whether or not that inefficiency is offsetted by the extra efficiency garnered into the electrical supply system by the improved power factor?

 

[jpanhalt]

In your own words from that thread:

but thats* a fantastic reduction.....lighting is an enormous amount of power...so thats a huge reduction

*refers to an estimate of "reduce the total power by 1.94-2.58%"

Do you now disagree with that? You asked a question, which I think that article answers. Now, you seem to want to argue with that answer. Why did you ask the question, if you knew the answer?

Frankly, my first impression of this question reminded me of that old puzzler, "Why did the chicken cross the road?" In this case, you are aided by the fact the On-semi, Texas Instruments, and other manufacturers of such control units have information lines. If you really want the answer, why not ask the manufacturers?

John

 

[Flyback]

I think the manufacturers will recommend people buy their pfc IC offerings as it makes them money.
To be truthful, I have no idea how much energy is wasted in the elec supply system due to all the non PFC'd lighting loads. I certainly wouldn't be able to calculate it.
Certainly discussion of PFC on any forum seems to make people generally very unimpressed, and the concensus of opinion appears to be that PFC is only worth doing (from an energy saving viewpoint) for large industrial complexs using enormous amounts of power.

 

[jpanhalt]

I think the manufacturers will recommend people buy their pfc IC offerings as it makes them money.
To be truthful, I have no idea how much energy is wasted in the elec supply system due to all the non PFC'd lighting loads. I certainly wouldn't be able to calculate it.
Certainly discussion of PFC on any forum seems to make people generally very unimpressed, and the concensus of opinion appears to be that PFC is only worth doing (from an energy saving viewpoint) for large industrial complexs using enormous amounts of power.

Well, it appears you have answered you own question fully.

John

 

[Flyback]

but not about eg, things like, whether its just because they don't want primary side electrolytics.

also..
Post #3 of this thread presents an idea for a new type of wall dimmer which preserves power factor throughout dimming....
https://www.electro-tech-online.com...ghtbulbs-are-damaged-by-triac-dimmers.139049/

..however, as you can read, better minds than mine thought the idea was poor.
If PFC really is king for light bulbs, then my new dimmer should be sailing into the market?

 

[ronsimpson]

If PFC really is king for light bulbs, then my new dimmer should be sailing into the market?

What ate you doing to make that so? (not counting electro-tech-online.com)
Wow are you patents coming?

 

[Flyback]

im not sure what the elec supply system energy savings would really be like for pfc in lighting. thus don't know if the pfc dimmer is worth it.?

 

[Nigel Goodwin]

im not sure what the elec supply system energy savings would really be like for pfc in lighting. thus don't know if the pfc dimmer is worth it.?

Perhaps you should try reading back in the multiple threads you've posted about the subject?.

There are NO savings for the domestic customer, only for high user commercial ones - there's no PF metering on domestic premises.

The requirement for PFC is for efficiency and money saving for the electricity companies - which is presumably why modern TV's have PFC, and presumably why it will become more and more of a requirement.

 

[Flyback]

yes I read those, and it concluded that the energy saving would be 1.94-2.58%.
The problem is that the effect of doing pfc in a led lightbulb, is that it makes the bulb about 2-2.6% more inefficient..so it seems to cancel the benefits of pfc.

The problem with pfc'd led bulbs is that their lack of primary bus capacitance, means that their input emi filters ring like mad when connected to triac dimmers, or whenever switched on...thus they need energy dissipating dampers...also, pfc'd flyback bulbs have higher rms fet current, so more losses there.

Im really not sure if the 1.94-2.58% saving due to doing pfc is not just wasted by the extra inefficiencies of a pfc'd bulb..in fact, I doubt theres much overall saving if it really is just 1.94-2.58% as quoted here

 

[cowboybob]

One of my more recent jobs was as Energy Manager for a research facility with a 2MW HVAC/Building ancillaries power plant.

Just a note from the IEEE for your perusal concerning PF and electrolytics (at **broken link removed** ):

"This paper proposes the use of a single-stage high-power-factor converter for power LEDs, without electrolytic DC bus capacitor. The power factor correction is obtained through direct connection of the Boost inductor between inverter stage and two input capacitor. A rectifier with output capacitor filter connected between the inverter stage and DC bus capacitors is used to obtain DC current in power LEDs. Experimental results are presented to prove proposed design methodology." This is just the abstract. You have to buy it to see the full text.

From jpanhalt's posted site note the 20% world power usage for lighting is a figure that's going to be difficult to recoup from the users (us, you and me).

At my job above, our power bills for the HVAC facility had both KWh and KVAh cost components listed seperately. To do this they power meter was designed such that those values were seperatelty monitored. We had a PF correction cap bank that kept our PF at o.96 to 0.99 quite well.

Domestic meters, however, only monitor KWh. In order for the utilities to recoup the PF losses the meters will have to be, of course, replaced. I am going to assume that the utilities, due to the enormous costs for such a move, won't do it.

Thus, as with incandescents (which do not alter PF but are inefficient), PF altering lights will become illegal by law or caveat and we will have no choice in the matter but to use the , inevitably more expensive, alternatives.

Just sayin...

 

[cowboybob]

I forgot to add that whatever our peak KVAh was for any given month became the KVAh value for all subsequent months for 1 year, irrespective of our actual use.

Not bad for the utility company, eh?

Forced us to retrofit the two chillers with "ramp-up" starters (at no small cost) to avoid the huge inrush currents from dead stop full power starts.

Our payback time for this was 11.3 years, assuming no power usage price increases .

<EDIT> Oh yeah, forget to add the utility claimed the "peak" penalty was to cover maintenance of the delivery grid to assure our "overages".

HUH??

 

[ChrisP58]

One reason for small lamps to be PFC, is because small lamps are often strung in parallel to cover an area. Even though you may not be mandated to use PFC for a 7 watt lamp, put twenty of those together and you now have a 140 watt lighting load. Put many hundreds of those throughout a building, and the improved efficiency that PFC has on the power distribution system will outweigh the small reduced efficiency at the lamp.

 

[alec_t]

im not sure what the elec supply system energy savings would really be like for pfc in lighting

Perhaps you could run a sim of a modelled lighting unit with/without pfc and do the sums?