800W SMPS with no Power factor corrector

[eem2am]

Hello,

i have just seen an 800W offline SMPS for class d supply.

It had no front end power factor corrector.

How can it be ok to endure such huge mains rectifier currents?

...the 680uF input caps surely cannot be rated for that level of RMS ripple current?

(I wont name the company, as it would be wrong of me to do so )

[hesener]

most of the time it will run at maybe 100W or less. the (silicon bridge) rectifiers usually can handle very high peak currents, e.g. the GBPC25 supports RMS currents of 25A but peak currents of 300A. The datasheet says non-repetitive, but that really means that the cycles should come in slower than the thermal time constant in the system, and audio crescendos usually meet that requirements. So, its not unusual....

just my two cents...

[runebivrin]

And an 800W power supply is nothing extreme in itself. The fact that it's a SMPS doesn't change that even if it does allow for greater ripple currents if the regulation is well designed.

[eem2am]

Here is the SMPS in question


https://www.coldamp.com/store/media/...tasheet_en.pdf


...you can clearly see that the choke at the input is not a boost converter PFC choke, because it has the bit of margin tape separating the live and neutral.

800W is actually pretty big for a switch mode power supply.

.......For 800W SMPS, a single stage boost PFC is usually not sufficient to handle the thermal situation......since a simple Boost PFC has just one FET.

.....also, a Boost PFC is the stage right next to the input line........so often the fet switching transition has to be more heavily damped to avoid high harmonic conducted emissions going back into the line...this means the fet getting very hot.

Typically, a boost stage is needed anyway (even if not power factor corrected) after the mains input, so that the rectifier currents are brought down from being sky-high.

Also, having a boost stage up front, makes life much easier for the downstream converter..........easing its design considerably....since it has a nice stable Vin to switch from.

[ssanmor]

For audio purposes, PFC is not mandatory.

This PSU has been tested at CONTINUOUS power levels above 1KW with no problem, and >1.5KW audio. In fact it is pretty robust. The components are rated for much higher currents than the specified available power.

PFC could be added for convenient world-wide mains usage, but we prefer to keep efficiency high and switch the range manually: for users with 100-120VAC mains voltage, voltage doubling can be setup with a jumper. Even in this case full power is available, although currents will be higher so we prefer not to use this mode for continouous (non audio) applications, but to provide a PSU/transformer specifically designed for this mains range, so no voltage doubling is required.

As a curiosity, SPS80 is even being used for military applications (not audio, but to power electrical submarines), in harsh environments with high temperatures, sudden full-load and load-removal, etc. These units are identical to the standard units you can buy, and they are working in a 4-units series configuration (for 400V/8A output) in that applications for 4 years now flawlessly.

We are preparing a new improvement to our SPS series of PSUs that will reduce their already low EMI, based on spread spectrum
techniques.

Sergio Sanchez
www.coldamp.com

[eem2am]

Hello Sergio, the quality of the SPS80 SMPS is obviously very high.

-However, it is illegal and could not be publicly sold in most countries in the world.


Unfortunatley, SMPS's for sale to public consumer markets must all be power factor corrected if above 75W.

This is a blanket rule, that covers all SMPS's for public sale......

-its an unfortunate rule, because most guitar amp applications don't warrant its use (PFC), but unfortunately the regulatory bodies would move in and ban SPS80 from sale to the public.

-as you rightly point out, military customers, in submarines etc can use anything they want, since military considerations are obviously different.

[ssanmor]

Thanks, eem2am. I assume you are referring to the infamous EN61000-3-2. As you said, this is a controversial and not clear at all regulation.

Well, it specifies (in the latest revisions) that Audio equipment is classified as Class-A. The harmonics regulation (that would practically require active PFC) apply when continuous output power is 75W or more. In audio applications, the relation between max. instantaneous power (the "800W" rating) and continuous or rms power is very large, in excess of 10 or more, and in any case not clearly defined. In any case the equivalent of 75W continuous power in audio would lead to an impractical level unattainable with music.

Our PSUs are for audio uses (you can use them for other applications and, if they are not military, an active PFC connected at the input is recommended, under user's responsibility). So it then comes to a matter of definition of continuous vs. instantaneous power capability, integration time, crest factor, etc.
We all agree that having a PFC front-end is better in terms of current-draw quality from the mains line, but it is detrimental from an efficiency point of view, not to talk about costs and size. Having PFC in a PSU of this power level will almost for sure double its price and force a much larger size.

In any case, if the above reasons are not enough, let me say that most audio SMPS manufacturers of proven reputation don't use PFCs in their higher power ranges of PSUs, and if they do it is only for lower power units and/or where automatic range-selection is a customer requirement. As a well-known example:

http://www.hypex.nl/docs/SMPS1200_datasheet.pdf
http://www.hypex.nl/docs/SMPS3k_datasheet.pdf

In these cases we are now talking about 1.2KW and 3KW audio rated SMPSs (really 400W and 1KW continuous, respectively, so we show a fair comparison with our products) with no PFC. I am sure Hypex is also aware of EN61000-3-2 and they have done their homework and determined that PFC is not mandatory for this kind of products.

[metalsculptor]

800W off line is small, most industrial frequency converters are off line I have seen 6000uF effective straight across a 650V DC bus, the power factor is terrible and the makers usually advise the use of a line reactor to improve things. It would be nice if makers would use a PFC but if devices of over 100 KVA can be run off line then 800W shouldn't be a problem unless the capacity of the outlet is exceeded.
It make little sense to set arbitrary wattage limits for domestic PFC use when the aggregate wattage of poor power factor devices is so high., think of those horrible CFL's and computer power supplies, even the inverter air conditioners or their bigger cousins the chiller.