Audio SMPS with PFC is overengineered?

[eem2am]

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......

http://www.hypex.nl/docs/SMPS180_datasheet.pdf

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..........................

https://www.coldamp.com/store/sps80.html

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.

[darkfenriz]

Originally Posted by eem2am

Hi,

.....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.

Both volume and price of electrolytic capacitors are more or less proportional to their CV^2, ie. energy storage.

Otherwise I agree with what you've written, PFC is welcome but good transient response and low 100Hz ripple are essencial.

P.S. It is always up to engineer how they obtain norms compatibility, switched PS, linear PS, PFC or not.

[eem2am]

However, i still believe that the SMPS180 would have been cheaper to make if they had placed some capacitance on the primary side to hold the voltage up there, and gotten rid of the PFC aspect....even if that primary side capacitance had to be rated to 400V because of the 90-265VAC input range.

Of course, you are right, and I have no critisism for the engineer, just wondering why i should be prepared, as a potential customer, to pay extra money for a feature which i dont want and dont need.

Since the Active PFC means higher RMS input current, this will in fact tend to make efficiency worse, so we cannot even say that that that the SMPS180 has particularly green credentials.

Does the company anticipate the forthcoming of PFC regulations for audio equipment i wonder?

[darkfenriz]

Audio amps are defined as "class A" according to IEC61000 harmonics content regulation.
These are a bit looser requriements on power clarity compared to eg. computers.

I believe some audiophiles would like PFC for better quality of power supplying other equipment, like CD player, some others are foolish enough to want it because someone told them something.