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Old 26th December 2011, 03:29 PM   #1
Boscoe is offline Boscoe  United Kingdom
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Default SMPS for audio.

I have been looked at SMPSs for my current venture on the Connexelectronic website when I saw it said they were only capable of half power on each rail at one time. So a 500W SMPS will only be able to offer 250W at a time. I'm not trying to have a dig at Christi here just trying to work out what I'm doing for my design. Link for the 500W SMPS datasheet.

So if I have a 100W amp into 8ohm I need 28Vrms or 40Vpk so I need a minimum of 40Vdc rails +15Vdc for headroom plus rail sag. So 55Vdc and 5Apk for a 100W to the properly powered, overall I need a 275W PSU but as I can only use half power on each rail I will need a 550W SMPS correct?

For example a regular 300VA toroidal traffo I assume you can pull 300VA on each winding one winding at a time as the only limiting factor is the flux density not to do with the windings?

Thanks
Boscoe
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Last edited by Boscoe; 26th December 2011 at 03:32 PM.
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Old 26th December 2011, 07:50 PM   #2
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"For example a regular 300VA toroidal traffo I assume you can pull 300VA on each winding one winding at a time as the only limiting factor is the flux density not to do with the windings?"

No, flux density doesn't change with load significantly.
The limitation is the resistance of the secondary.
If you need 300va from a 300va dual secondary transformer, you must parallel the secondaries.

The same goes for any smps. if you need full power from one rail, you will have to turn it into a one rail power supply. this means paralleling the secondaries, diodes, output capacitor, output inductor, etc.
For an unregulated power supply you can probably get away with such a modification.
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Old 26th December 2011, 08:24 PM   #3
Boscoe is offline Boscoe  United Kingdom
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So your saying so many amps are under powered massively?
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Old 26th December 2011, 08:32 PM   #4
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Quote:
Originally Posted by Boscoe View Post
So your saying so many amps are under powered massively?
no you assume when building the amp a 500 watt smps is the max wattage w/e you plug into it will use.
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Old 26th December 2011, 08:37 PM   #5
Boscoe is offline Boscoe  United Kingdom
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So what's the point in building a that power amp?
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Old 28th December 2011, 10:54 AM   #6
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not sure what you're trying to say. for the most part when you acquire a dual rail supply it is implied that the complementary outputs will be loaded approximately equally, when averaged across the thermal time constants of the circuitry involved.
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Old 28th December 2011, 06:18 PM   #7
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I am able to pull 13 Amps with 125VDC from my unregulated SMPS with 25V Drop at this load. from +-74VDC with no load

Drawing 800W with AB amplifier SMPS drops around 10 ~ 13VDC with music.
20Hz Sine wave 14V DC drop.

However, SMPS is 1KW max power, but over driving my SMPS is a big joy for me

Good luck
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Old 29th December 2011, 12:53 PM   #8
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Excelent description from Connexelectronic of their smps..........(from your link above)......they go to the top of the favourder list now because of their transparency.

Though it says its "Series resonant" and "LLC resonant"........but these are two different types of SMPS.....so which one is it, we should like to know.

Other points......


there is a rather wide variation in V(out).....why is this, i can see a TL431 secondary side error amplifier....so why such a variation in V(out)

Also, i cant see a MOV in the mains input stage.

Also, i cant see balancing resistors across the input electrolytic capacitors.

Also, the bias winding is single phase rectified, whihc means DC is being drawn from the transformer, which is not a good idea.

Also, it'd be great to get the datasheet for those 820uF input electrolytics, so that we can see the ripple rating, and know what continuous power we can use the SMPS500 at without cooking those electrolytics.

Also, an FFT of mains input current harmonics at 1/8th power (500/8 Watts) would be nice so that we can see if it violates mains harmonic current limits for class A equipment.

Anyway top marks to Connexelectronic for their transparency.

Also, any 5% load to 100% load transient response scope shots would be nice, showing undershoot and settling time. (plus 100% to 5% scope shots too)
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Old 29th December 2011, 04:43 PM   #9
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Another point about the SMPS500 is that its voltage mode controlled......these are always of slower transient response than otherwise equivalent current mode smps's -so i would be surprised of SMPS500 was the optimal solution for a class D amplifier supply which needs a fast transient response.
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Old 29th December 2011, 05:28 PM   #10
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Default Input electrolytics of SMPS500

Also,
If the input electrolytics of the SMPS500 (with the mains changeover link fitted) are the SMQ series 820uF, 200V, then these have only 2.37 Amps of ripple current capabiliy at 50Hz.

If the load is continuously more than just 170W, and the mains is 98VAC, then these electrolytic capacitors are going to get destroyed by overheating very quickly.

So i cannot understand why this SMPS is called "500W"....because the input electrolytics alone cannot manage any more than 170W continuous.

SMQ series 820uF, 200V capacitor:
http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/005-snapin/al-smqlug-e-110701.pdf
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