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Old 28th September 2005, 01:42 PM   #101
Pierre is offline Pierre  France
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In fact, if I am not wrong, dissipation in the resistor depends more on the cap value.
Typical snubbers range from 2.2 ohms to 100 ohms. The lower ones can be found in ATX psu's, and are 5W maximum. (although they are half bridge and that must suppose a great difference as the voltage is halved).

The formula for max. power dissipation in the resistor is, according to my references,

Pr=f x C x V^2

min. power is Pr=4 x C^2 x V^2 x f^2 x R

The same references say that the typical power is about half of maximum typically (I suppose it depends on the magnitude of the absorbed ringing).
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Old 28th September 2005, 02:11 PM   #102
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by Pierre
In fact, if I am not wrong, dissipation in the resistor depends more on the cap value.
Typical snubbers range from 2.2 ohms to 100 ohms. The lower ones can be found in ATX psu's, and are 5W maximum. (although they are half bridge and that must suppose a great difference as the voltage is halved).

The formula for max. power dissipation in the resistor is, according to my references,

Pr=f x C x V^2

min. power is Pr=4 x C^2 x V^2 x f^2 x R

The same references say that the typical power is about half of maximum typically (I suppose it depends on the magnitude of the absorbed ringing).
When this SMPS switches, it switches more than 600V as it is a bridge type. Depending on how fast it switches, dissipation will be more or less. Can do some measurements on the waveforms sometime. The dV/dt slope should determine what current flows through the cap and the R and thus the voltage drop over the R can be calculated and thus the amount of power dissipated during each switching event can be calculated and that can be multiplied by the number of switching events. A rough calculation I did predicts something like 5W power dissipation when the 600V switching takes 300ns and when the switching frequency is 150kHz.

Best regards

Gertjan
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Old 20th October 2005, 04:21 PM   #103
fredos is offline fredos  Canada
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Default Solve pumping effect...

Hello guy

You can see news picture of my 8000w amplifier on my web site (www.d-amp.com). Thank's to all guy who have reply to job offer, I got my guy!

For all other who ask me question about design, most of them was about pumping effect on single ended amplifier...I can give you my trick on my first series, I'm now in 4 quadrant output stage, so no more pumping effect.

The simple way is too add a small switching power supply who return (clamp) the amplifier bus voltage to the bulk capacitor of the main switching power supply. The trick is that if you have a voltage doubler main switching power supply (means 340V), and for example +/- 90V amplifier power supply, you just design a 180V (sum of the +/-90V) to 330V power supply. If amplifier rail go over 186V, the impédance of the main line will ''clamp'' the voltage trought switching. A simple IR2153 with a pair of IRF640 and a TN29/19/7.5 toroidal will do the job.

In that way, you will clamp amplifier rail with very high effiency! And best, return this energy to power supply...Think about this!

Another trick I have use in my model 2000, is to simply add 2 more turn on the output filter (speaker side) with 2 MUR840 diode to clamp to the power supply. This will saturate the coil when speaker feed back their energy to the amp and force amplifier to compensate (if you use analogue feedback instead of ''digital'' feedback!).

So thank's to Dan Blouin to join the D-Amp team!

Have a nice day!

I share some trick, so dont think I'm here to take you idea and the money!

Now, just to know if someone have built amplifier with analogue feedback and have some waveform probleme ( on the scope) over 10Khz....But amplifier pass distortion mesurement...Weird...I work on this now....

Bye

Fred
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Old 20th October 2005, 05:48 PM   #104
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Fred,

You manufacture impressive products.....

Can you tell me more about your design? Fixed frequency, full bridge?
Pre or post feedback?

BTW, do people really need more power as 2kW in 4 ohm??

Regards,

Jan-Peter
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Old 20th October 2005, 08:27 PM   #105
fredos is offline fredos  Canada
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Default Hi Jan Peter

I use fixed frequence forced oscilation at 250Khz for my first series and 500Khz for the HVI serie. First serie are in half bridge with the trick I described in last post. Second serie is full floating full bridge with reverse side tighted to ground, so you can bridge amplifier if you need more power (????). Power stage is all isolated from drive circuit by optocoupler and power supply provide regulated floating 190V. For now, my 8000HVI is the better seller. 4000W in 4 ohms is more than most speaker can handle, but a stack with 4x 16 ohms speaker per side is impressive. If you dont run amplifier in limiter all the time, most 18'' of 600W handle it. When run at full power, ie limiter go on at each bass kick, most speaker ''fuse'' in less than 2 minute, no burn voice coil...At this time, only Eminence ''kilomax'' serie and Transparence NAC218 (www.tr.ca) handle that power for all night long.

More technic now...Power supply is half bridge with IXIS 500V 21 Amp mosfet with direct drive by 6N137 and Micrel Drivers. Control is SG3525 in voltage mode with regulation by secondary. Current limit is done with small current transformer, who limit the output voltage above 50 Amp at the secondary to limit power, but with a really slow respond time, about 30 second. So maximum power is reach within 30 second, after that, power go down to 670W per channel in 4 ohms. With music, each time that signal pass trought 0V, circuit is reseted. So no effect on music, but limit power on the bench for savage tech... after 30 second. Another circuit sense current and voltage waveform at the main AC supply, and when current wave is more dense that voltage wave, amplifier limiter begun active. This will prevent fuse and breaker blowing.

Last trick, another circuit sense current in the speaker and when current ration is over range, meaning that speaker voice coil is out of is tolerance, limiter is actived too. Some kind of speaker saver, for short time.

For all who ask for schematics, I'm sorry but I have work 6 years on this amplifier, so I can give you lot of cue, but no schematic....You know that I'm in advance over Crown, crest and peavey, I whant to keep it! Sorry for guy who work here!

Have a nice day!

Fred
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Old 20th October 2005, 09:04 PM   #106
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Quote:
Originally posted by Jan-Peter
BTW, do people really need more power as 2kW in 4 ohm??
More is better, don't you know it?

Pros tend to have many amps with reasonable power instead of one gaint.

BTW: Just read the data. It makes me wonder because some things sound not right.

97.5% effeciency and 7800 watts or?

9600 Watts and 110/220 volts AC? Is that possible in the US, sure not in Europe??
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Old 20th October 2005, 09:33 PM   #107
fredos is offline fredos  Canada
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Smile Hello peranders

4800va per channel is the maximum instantanous consumption recorded in amplifier with music at hard clipping....Sorry for this, I will try to update web site to make this more simple....Sound like some people call peak power....All high power test have been done with 240V 30 amp main supply...The fuse saver in amplifier limit output power to avaible power source...So dont expect more than 1800W RMS total on 120V 15A outlet, but peak at 4000W per side is theire!

Bye

Fredos
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Old 20th October 2005, 10:06 PM   #108
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I thought it would be peak.

Could you also clarify what you mean on your site by "inductive and reactive power includes", that'd be VAR or something no?

Thanks,
Chris
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Old 21st October 2005, 06:10 AM   #109
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Default Re: Hi Jan Peter

Quote:
Originally posted by fredos


I'm sorry but I have work 6 years on this amplifier, so I can give you lot of cue, but no schematic....You know that I'm in advance over Crown, crest and peavey, I whant to keep it! Sorry for guy who work here!

Have a nice day!

Fred

Hi Fredos,

You had worked hard for 6 years and now enjoying the Fruit of Class-D at Kilowatt power levels and that is your Right too....

But Have you visited http://pro-audio.powersoft.it/ these guys had 12KW [12000Watts]CLASS-D amps in 1 U rack space featuring Centifugal Blowers for cooling instead of axial fans...

one more question,
Did your Class-D amps feature 2 LEVEL PWM or 3 LEVEL PWM when they are bridged?

Keep it up ,

regards,
K a n w a r
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Old 21st October 2005, 07:31 AM   #110
fredos is offline fredos  Canada
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Smile Hello Workhorse!

I know powersoft...I already made some test on their 7Kw amplifier, the first serie I think...Not impressive...First, output was not thighted to ground and have a potentialy dangerous DC voltage, referenced to AC and input ground, and second, explain my why, on the bench, they only put 222W RMS in 4 ohms...Something wrong??? I dont know....On music, they seem to peak near 2Kw 4 ohms per side, but bass is very lean, very noticiable with hip hop music whit ''fat'' bass (maybe rolling bass in english???). On other music, like rock with good attack bass, it was a bit impressive, but compare to a Crown VZ5002 (my reference to overkill!), nothing to compare...I dont know about new serie, I cannot find nobody who buy it in Quebec....And yes, I run it on 240V....But one very good thing, the amplifier look very nice inside, I like the way that they have built it....

Nice for their 12KW, but by experience, for now 4KW per side is a bit dangerous for majority of speaker, so except with serie-parrallel speaker, maybe no use....And pro dont made serie-parrallel, at least 4X 16 ohms speakers, what most use on my amplifier.

But just for fun, not for production, I will plan to make maybe a 10KW mono amplifier with SGS thompson fet, the STE53NA50, With the same circuit I use in my 8KW, but at 350V...Could be nice to develop it just for fun, in 1U...

To give you an answer, I only drive my power stage with 1 level PWM, out of phase for each side of my bridge topologie. That means that 1 side of H bridge provide power to speaker and other side shift the DC bus voltage above and under ground reference, just like a conventional full bridge amplifier, but on side to ground and the other to speaker. That's why I use floating power supply. It's the same power as a half bridge at +/- 190V.

By the way, you maybe find that my english is not perfect, but sorry, I speak french!

Thanks!

Fred
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