Audio SMPS with PFC is over-engineered?

[grizedale]

Hi,

I have just seen the datasheet for a 180W (peak) offline SMPS which comprises a single stage active power factor corrector...

here it is, its the SMPS180 by Hypex......

**broken link removed**

I cannot , for the life of me, understand why Hypex have made a Power Factor Corrected SMPS for Audio usage.

There is not a single country in the world that requests Power Factor Correction for Audio usage.

Since this (single stage) SMPS is power factor corrected , it will comprise a dreadfully slow feedback bandwidth, (~10Hz)which is totally unwanted in audio applications, where good transient response is required.

In the datasheet, Hypex extol the virtues of them having the bulk storage capacitance on the secondary side...........

.....i can't think why they believe that this is virtuous, the entire switch-mode industry knows only too well that capacitive storage banks are best placed where you have the highest voltage...........generally at the mains side.
Capacitive energy storage quadruples with doubling capacitor voltage because of the square law of capacitive energy storage.

The lack of capacitance on the primary side of the SMPS180 means that it is harder for the SMPS180 to filter the high frequency switching harmonics from the mains....i'm not saying it cant be done, but your hampered by the lack of primary side capacitance.

The SMPS180 will, however, reduce mains harmonic current levels, in comparison to a non-PFC design.........however, what on earth is the point of doing this when the regulatory bodies have no requirement of it.?

A PFC design will be more expensive and require more engineering effort than a non-PFC design, and since there are no advantages in the Audio world of using PFC designs, why have Hypex chosen to do a PFC design.?

Perhaps i am being too cynical there, the inrush current will be less with a single stage PFC design....however, inrush is easily circumvented with NTC's.

One point about Single stage PFC design is that the peak FET currents will be higher, and the transformer will need to be bigger.
The FET RMS current will also be higher, and a bigger FET heatsink, or more expensive low RDS(on) FET wil be required.

Can any reader think of a reason for using the SMPS180 in an Audio application?

Here are Audio SMPS's of several 100W's power level, which have no PFC stage..........................

**broken link removed**

ALC0180-2300

The deleterious point about Hypex SMPS180 is that it is a *single stage* PFC design............if it had comprised a PFC Boost converter, followed by a downstream SMPS, then that would have made sense, since the high voltage bus provided by the Boost PFC stage, would mean a convenient high input voltage for the downstream SMPS stage, which would allow it a very good transient response.

 

[FvM]

EMC regulations requiring PFC for power supplies in the respective power range have been discussed in a previous thread. https://www.edaboard.com/threads/217337/
As far as I'm aware of, at least EU regulations require PFC in this case. I assume, that Coldamp as a spanish manufacturer should know about this stuff.

Referring to technical aspects, a single stage PFC PSU as the Hypex SMPS180 will obviously expose a higher 100 Hz ripple than a standard non-PFC PSU, similar to a classical transformer power supply, if comparable capacitor values are used. Slow bandwidth must be feared with a simple voltage controller, but could be avoided with a more sophiscated design. Power feedforward can achieve a good transient response without corrupting the sine current waveform under constant load conditions. In so far, PFC isn't contraindicated for audio applications in my opinion.

The large secondary capacitor requirement of the single stage PFC design may be a reason to prefer a two stage design, at least if targetting to compact form factors. The problem of PFC transient behaviour still exists in this structure.

 

[grizedale]

OK Thanks.......

FvM
"Power feedforward can achieve a good transient response without corrupting the sine current waveform under constant load conditions."

I agree, however, audio amplifiers for electric guitars are about as far from a constant load as you can get.

Thankyou for pointing out the earlier post about PFC for guitar amplifiers.

-though that post was inconclusive about whether or not PFC is required in Europe for guitar amplifiers.

I can state that i have taken apart quite a few electric guitar amplifiers of 100 to 800 W and i can absolutely assure anyone that they contain SMPS with no power factor correection whatsoever, and these are sold in Europe and the world over.

I would be willing to pay good money for an actual official document that states whether or not electric guitar amplifiers are exempted from PFC laws....and one that states the limits for mains harmonic currents in audio SMPS.

But no such document exists, and the EN documents just talk generally, making it impossible to know.

 

[Orson Cart]

Since the policing of EU standards is complaint driven, unless someone complains that audio gear above 75 watts does not comply with the harmonic requirements - then the selling of it will go on, however the importer has to declare it does conform - so he/she is taking a risk there, if they are selling to the general public - a lot of that gear may well be bought online overseas and shipped in - so it goes under the radar , so to speak.

Where you have a lot of high power audio gear in one place it makes sense to have it PFC, espeically if you are relying on generators to power it if the mains goes off. Regards, Orson Cart.

 

[FvM]

Since the policing of EU standards is complaint driven

In my view, they are driven by the idea of manufacturer responsibility.

It seems obvious, that the general PFC regulations have to be applied to audio amplifiers. I don't see technical reasons that can be hold against it. If you want to know more, ask Coldamp sales people for their declaration of CE conformance, or ask explicitely, if their products comply with EN 61000-3-2 Limits for harmonic current emisions (equipment input current <= 16 A phase).

without corrupting the sine current waveform under constant load conditions

There's a possible misunderstanding. I was referring to the fact, that input current waveform necessarily differs from a sine during load transients. This are however non-harmonic distortions. But it should show a clear sine current with constant load and fast transient response. This can be achieved by the combination of a slow voltage control loop and a fast load power feedforward.

 

[grizedale]

FvM,
"In my view, they are driven by the idea of manufacturer responsibility."

Thankyou, but i tender that you may agree that its nothing to do with being "responsible"

....PFC Audio SMPS is a down right bad idea for the environment and for global warming.

Even an audio SMPS supplying guitar amplifiers of several 100 Watts peak power only consumes around 20-30W on average.....and mostly less than that.....so having a lossy active power factor correction stage at the front end is very inefficient indeed.

When average powers are so low, , then from an efficiency, energy-saving point of view , it makes utterly and absolutely no sense whatsoever to make SMPS for guitar amplifiers have active power factor correction..(evern at 100's of Watts)..unless that is, we really do want to go in the direction of melting the polar ice-caps and starving the polar bears more.

 

[FvM]

I had forgotten, that audio amplifiers are explicitely mentioned in EN 61000-3-2. In so far, it's even more clear, that they are covered by the PFC regulations.

Unfortunately, EN61000 doesn't rate average power consumption. There are clauses for short time operated devices, e.g hair dryers. But at least for the single stage PFC, I won't assume lower efficiency of a PFC design in general.

 

[grizedale]

Thanks.

its spec'd for "audio" but i believe that electric guitar amplifiers are exempted?

 

[FvM]

i believe that electric guitar amplifiers are exempted

Do you have any indications for this? I don't know why.

 

[grizedale]

yes ive taken apart many mains connected guitar amplifiers of 100W+ and inside , the SMPS has no PFC.

These are currently sold evrywhere in the world as well as EU.

EN61000-3-2 does not go into what should be done for smps with a <<<75W average power , even if there peak power is 300W+.

So Guitar amps are exampted.

There simply are not enough sold, and the average power is so low, that the EN body would never manage to uphold PFC for guitar amplifiers.

The EN people are reasonable engineering professionals who would not put a company out of business for producing non PFC guitar amplifiers.

 

[FvM]

I fear, your interpretation of EN 61000-3-2 can't be founded by the text. The standard doesn't refer to average power. Real power is understood according to the glossary as instantaneous value averaged over one mains periode. In my view, it's obvious, that the device's nominal power counts for the 75 W limit.

The average power argument, if applicable for guitar amps, would apply for other audio amplifiers as well. For the harmonic current measurement of audio amplifiers, EN 61000 is referring to test conditions specified in EN 60065. I don't have the text, but apparently pink noise signals are prescribed. Unfortunately I don't know the specified power level, but up to half the amplifier RMS power would be feasible with pink noise.

Personally, I don't have ambitions to fight non-PFC guitar or generally audio amplifiers. Enforcing the regulation would also threaten classical tube amplifiers, that still hold a considerable share of the guitar amps.

 

[grizedale]

I can assure all that Mains connected Guitar amplififers are classed as "portable audio equipment" and are exempt from Power Factor Correction (EN61000-3-2)

Page 5 of the following (near the bottom, tells of this)

 

[FvM]

Thanks for linking the document. Unfortunately you are misunderstanding the commas.

Household equip., tools excluding portable, audio equipment?

spells "tools, excluding portable tools", not "portable audio equipment", which isn't a category of EN 61000-3-2. The description of Class A under 5. Classification and limits on page 6 clarifies. Sorry for that.

 

[grizedale]

Thankyou , you have sharp eyes indeed.

So it seems to be Class A is audio...... and i presume that Guitar amplifier manufacturers must be self accrediting when they market 350W guitar amplififers without PFC?

In other words they own their own EMC lab, and pay the regulatory bodies for a licence) and simply pass their (non-compliant) products through...is this the case i wonder?

 

[FvM]

In contrast to stage PA devices, that can be considered as "professional equipment" above 1 kW, there's no backdoor for guitar amps, I think. I previously suggested to ask the manufacturers for their declaration of conformance. I'm curious, which CE regulations and technical standards are referred by them.

Historically, CE compliance of electronic devices was mainly targetting to EMC in early 90s. Power quality regulations came up later. If you ship your product with a declaration referring to the EU low voltage directive and a number of technical standards, only a few experts will ask what's probably missing.

 

[grizedale]

Hi,

The following two documents, confirm that PFC is not a requirement in the world of Audio for <600W.

EN61000-3-2 states "75-1000W" needs PFC but does not state how that is measured....EN61000-3-2 states that you must draw >75W "continuously" in order to need a PFC stage....guitar amps with nominal power of ~400W definitely don't draw >75W continuously.

DOCUMENT 1:-
**broken link removed**

"2. Is power consumption continuously in the range of 75 W to 1000W?
Note: consumption is only considered (for all phases) during normal operation. Operation under extreme conditions or the rated power of the equipment are not considered. In other words, we only consider the real consumption of the equipment."

"10. Equipment with a rated power input of up to 600W are really at the limit of requiring PFC."

DOCUMENT 2:-
PowerPhysics Audio Electronics - Lab Notes - What is Power Factor Correction (PFC)?


"PFC is required by the European Union CE mark for amplifiers greater than 600 Watts"