800W smps with no PFC?

[grizedale]

Hi,

Here is an 800W offline SMPS with no power factor correction.

**broken link removed**

-How can this amp possibly last?

The diode bridge current peaks must be sky-high.

Also, even though there's 1.36mF of capacitance after the mains didoe bridge, surely the input ripple current will stress that capacitance at 800W input.

Surely it would have been better to do away with the selection switch which selects 120VAC or 240VAC, and just put a simple boost converter at the front end, with a 400V output?.........it wouldn''t even have to be properly power factor corrected.

And would you say that it looks liek an LLC resonant converter?

 

[FvM]

800W with simple input rectifier is quite common for single phase input motor inverters. They are available up to 3 kW output power. Input RMS and peak current will be respectively high, but manageable.

And would you say that it looks liek an LLC resonant converter?

Not at all. It's said to be fixed frequency (85 kHz) and no resonance circuit elements can be seen so far.

 

[grizedale]

Hi,

I can see a resonant cap and a resonant inductor.

The inductor has blue coated wire, the cap is a box cap and is next to it.

...the output inductors are just not big enough for this power rating.....also, the output is quite high voltage (+-58V) and this would give too high
di/dt with such small output inductors.

So this must be an LLC resonant converter.

Those motor inverters may well not have PFC.....but they likely have huge passive filters connected before them.....either that, or the general supply that they
draw from is power factor corrected

 

[FvM]

I can see a resonant cap and a resonant inductor.

I see a small FKP cap and a small inductor or transformer, maybe a gate transformer. I fear, you're jumping into conclusions. Of course, we'll need a circuit schematic or detailed specification to know exactly.

My general impression is, that the device has a somewhat scarcely calculated power rating.

Those motor inverters may well not have PFC.....but they likely have huge passive filters connected before them.....either that, or the general supply that they
draw from is power factor corrected

They usually don't have filters. Manufacturers suggest chokes when connecting to very low impedance grids to limit the peak currents, but they only sligthly improve the current waveform. It may be the case, that some large plants have harmonic filtering at their public grid interface. But this won't affect the current waveform of the individual devices.

Interestingly IEC 1000-3-2 respectively EN 61000-3-2 "bans" non-PFC devices, as least for the < 16A rated current range since 1995.

 

[grizedale]

Thankyou,

it is interesting that EN61000 bans non PFC devices, because all audio amplifiers for lectric guitars use non power factor corrected power supplies.
-they just use a big , 50Hz mains transformer, with a rectifier and big capacitor bank
-absolutely no PFC.

-So i am wondering, do audio amplifiers for guitars have an exemption?

 

[FvM]

-they just use a big , 50Hz mains transformer, with a rectifier and big capacitor bank
-absolutely no PFC.

-So i am wondering, do audio amplifiers for guitars have an exemption?

A transformer will improve the current form factor, but not sufficient to comply with the IEC/EN regulations. They are obligatory at least for the EU region. Exceptions exist for medical equipment, small power supplies (< 75 W) and professional equipment > 1 kW, e.g. industrial motor inverters. Guitar amps should be treated like computers, radio or tv receivers in my opinion.

 

[grizedale]

Well, i thankyou your words, though it is still inconclusive if PFC is needed for specific SMPS made specifically for guitar amps.

I would buy EN61000 document, but i don't know if it contains the specific question i have.

These documents are expensive and theres no way of knowing if my question ("do SMPS for guitar amps need PFC?) is answered in the expensive pages of this document.

Does any reader know where is the location of my required information?

 

[FvM]

I only have the initial 1995 (German) version of EN 61000-3-2, but the recent discussion and changes have been reported in various technical articles and EMI tutorial. I'm quite sure, that there's no exceptions for guitar amps.

 

[grizedale]

thankyou,

though this is very interesting , because i can assure people that guitar amplifiers above 75W are definentely not powered by power factor corrected power supplies.

So i am wondering what is happening here.

Guitar amplifier world is using 50Hz transformers with rectifier then big cap bank on secondary.....so the power factor is very low indeed.

-concerning SMPS, the word in the guitar amp world is that SMPS are not up to it to supply guitar amplifiers.......they simply cannot supply sudden overloads well enough....unless they are vastly overrated.