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Class D Switching Power Amplifiers and Power D/A conversion

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Old 5th December 2012, 09:52 PM   #131
fredos is offline fredos  Canada
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Already used cascoded emiter design for over 12 years in my amplifier... Now I use 2// BSC059N04LSG lo voltage device, with 2// HGTG20N60A4D IGBT high voltage device and APT30D60BHB freewheeling device... Only way I found to run amp at more than +/-100v... At +-/250V, I got 6Kw into 4 ohms... No way to go to 2 ohms... Simple 6N137/TC4421 driver.
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Old 6th December 2012, 03:59 AM   #132
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Hey guys since I have no other source of Internet other than my iPhone I will keep this post short. Have you considered a neutral point clamped half bridge. I have used this topology many times in high frequency (20kHz+) motor drive designs in the >100kW range with 900V busses and 600V IGBT modules. It would allow you to use 120V(20% margin) devices in +/- 100V applications, however your modulator will become more complicated. It is much more suited to triangle based modulators.... Will give more thought to hysteresis modulation and this output topology.
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Old 6th December 2012, 09:38 AM   #133
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Let's stay with the +/-80V level (say below +/-100V) .
Running such an amplifier bridged and stereo at full power will already cause visible fluctuations of the light in a normal house - if not already tripping the mains breaker...
In my flat I already saw the light changing when testing load steps of my last smps design, which was just 1.3kW.
With the intended design we would already be at the level of pulsating 4-5kW.

Both topologies (emitter switched and NPC) definitely have a better fit to higher voltages.
Of course one can build a NPC halfbridge for +/-80V, but I think the efforts especially for the three floating gate drives would definitely kill the goal to keep the design DIYable and remote debugable. Don't you think so?
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Old 6th December 2012, 09:39 AM   #134
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Hi Photonicube

Yes, but it is only usable as 2-level for class D as opposed to 3-level for motor control/inverter, possibly with a LF/HF split.
The huge downside is 3 floating 'high-side' channels.
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Old 6th December 2012, 10:11 AM   #135
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Good news!
There is a second source for the V30200.
The concerned vendor is using a C12H22O11-based 6" wafer technology and is likely to have a much more promising cost position rather than competitors with silicon based technologies.
Attached Images
File Type: jpeg 2ndScource.jpeg (33.2 KB, 477 views)
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Old 6th December 2012, 10:20 AM   #136
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C12H22O11 indeed! Environmentally friendly as well!!
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Old 6th December 2012, 10:24 AM   #137
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Planar too.
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Old 6th December 2012, 11:02 AM   #138
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"In my flat I already saw the light changing when testing load steps of my last smps design, which was just 1.3kW.
"
Light bulbs are very sensitive to small RMS voltage flicker. And the eye is very sensitive to small light changes. At 230VRMS, even 1V flicker can be visible, while +/-10 V changes would still be ok with most AC connected equipment..
I am not sure what your 2kW amp application is within your flat and if all your neighbours would like to dance to your special music ;-) but to avoid flicker, you may just choose a different AC phase for your amplifiers than for lighting.
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Old 6th December 2012, 12:37 PM   #139
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...I was just joking about my flat. In fact there alread my 60W rookie amps driving my 86db/W mini speakers are more than my neighbours can take

I am thinking more about the flicker standard DIN EN 61000-3-3.
There is a flicker curve given, which tells the max. allowed change of the mains voltage as a function of voltage changes per minute.
This curve was derived empirical with a large group of students as test persons. It describes the limit of voltage change which becomes visible when feeding a 60W light bulb.
Every drum beat will cause such a voltage change. Assuming 110 beats/minute the allowed voltage change is around 0.7%.
A mains which is stiff enough to change not more than 0.7% when beeing loaded with pulsating 4-5kW (stereo 2x2kW plus losses), is already beyond average.

I think 2kW (or may be 2.4kW) is a nice number for a high power DIY project. I am definitely not intending to push it higher.
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Old 6th December 2012, 03:43 PM   #140
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Back to circuit design:
For the simple configuration of just two MosFets I am using since years a simulation model which includes the relevant parasitics. Fit between sim and reality was not perfect, but good.
I extended the sim model to the circuitry with series shottky and additional freewheeling diode.
Attached a screen shot of the model and two zooms - showing high side and low side more detailed.
When using reasonably good freewheling diodes I am getting a mostly calm behavior. Even without any snubbering the wave forms remain good enough that the circuit should still work somehow.
The attached wave forms are showing the situation with the values of the shown schematics.
Means snubbering at the gates and across the freewheling diodes, but no snubbering at the MosFets. Also I put 2uF caps from the drain of the upper MosFet to the source of the lower MosFet, while the 100nH inductors model the wiring towards the e-caps and e-cap inductance.

Which real life experiences do exist? Is the configuration with series shottkys and fast soft recovery freewheeling diodes really that forgiving as shown in the sim? Please note, it shows the situation of 50A hard switching, not idle.

...have to check for a sim model of the V30200, from my understanding this diode should make the system even more calm...
Attached Images
File Type: jpeg Snubber_Sim.jpeg (207.5 KB, 455 views)
File Type: jpeg Snubber_Sim_HS.jpeg (74.6 KB, 424 views)
File Type: jpeg Snubber_Sim_LS.jpeg (72.0 KB, 405 views)
File Type: jpeg SnubbedWaveForms.jpeg (86.0 KB, 331 views)
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