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Old 12th May 2006, 05:12 PM   #101
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EVA,

Is that ferrite is the most suitable material for ClassD output inductor? What about Magnetics KoolMu or MPP, are they more suitable for this purpose than ferrite?
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Old 12th May 2006, 06:20 PM   #102
fredos is offline fredos  Canada
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Yes Eva, switching transformer are in #14 litz wirre with Shrink tubing over it for isolation!

Have a nice day!

When we will have picture of your project?

Fredos

www.d-amp.com
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Old 12th May 2006, 07:30 PM   #103
mzzj is offline mzzj  Finland
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Quote:
Originally posted by lumanauw
EVA,

Is that ferrite is the most suitable material for ClassD output inductor? What about Magnetics KoolMu or MPP, are they more suitable for this purpose than ferrite?
Performance is exellent but MPP and kool-mu are very expensive compared to ferrite or iron powder.
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Old 13th May 2006, 03:08 PM   #104
fredos is offline fredos  Canada
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Take a look at premiere magnetics...That was the best I have try and that's what I use.

Fredos

www.d-amp.com

They can make customs parts in small quantity (50-100) parts..
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Old 13th May 2006, 03:44 PM   #105
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Quote:
Originally posted by Eva
Workhorse, I recommend you to build a simple adjustable switching circuit allowing to measure inductances and saturation currents, if you don't have something similar already. Standard LCR meters and the like are not suited at all for gapped ferrites (or iron powder), they will always provide an erratic measurement.

I am experimenting with Gapped Ferrites yet !

Let you know the resultant outcome very soon....

K a n w a r
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Old 13th May 2006, 04:33 PM   #106
Eva is offline Eva  Spain
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Two quick prototype pictures. Vertical board is gate driver. Heatsink and IGBTs are under the horizontal PCB (only a pair of TO-220s currently mounted):
http://eva.eslamejor.com/t_sine19.jpg
http://eva.eslamejor.com/t_sine20.jpg

Capture of 10Khz output at the onset of slew rate limiting with 60V single power supply and a 4 ohm load. Shows output voltage and inductor current at 20mV=1A:
http://eva.eslamejor.com/t_sine18.gif

Note that this is not designed as an audio amplifier but as a full bridge low frequency motor driver that must operate on 330V DC single rail and provide 20A rms overload-proof output with little EMI and dissipation (they even want it without fans!) The output filter resonates at 3600Hz, yet the output is kept flat within +/-1.5dB up to 10Khz independent of load.

I use 60V for most tests since it's more comfortable to the touch than 330V. Switching spikes seen on the output voltage waveform are mostly due to filter capacitor inductance (400V wound foil types are not as good as the 63V or 100V stacked foil ones used for audio). Small spikes seen on current sense waveform are due to inductor parasitistic capacitance.
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Old 14th May 2006, 03:03 AM   #107
fredos is offline fredos  Canada
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Look good, but switching frequency seem low...About 80-100Khz as per current waveform, not suitable for audio!

Thanks Eva!

Fredos

www.d-amp.com
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Old 14th May 2006, 12:11 PM   #108
Eva is offline Eva  Spain
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Oh, it's intentionally done that way, frequency is dynamically controlled to achieve the lowest switching losses without exceeding a certain amount of output ripple voltage, and to score better in EMI emission tests. It will drop to 25Khz under normal operation at full load, as in practice the amplifier will be hardly required to produce any output above 1Khz.

I would operate it in a different way if it was intended for audio, as music allows for very high switching frequencies without too much losses due to its low average power content.
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Old 14th May 2006, 08:37 PM   #109
fredos is offline fredos  Canada
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So you use spread spectrum modulation? What determine the spread frequency? I wish ti maybe try this...Low frequency at low power, then higher frequency at mid power and low frequency again at full power, but I suspect ''beating'' problem between amplifier...

Fredos

www.d-amp.com
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Old 14th May 2006, 10:10 PM   #110
Eva is offline Eva  Spain
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With the average current mode control scheme that I'm employing, spread spectrum is not advantageous for audio as the poles introduced by the current amplifier are shifted down as frequency is decreased.

My frequency control is based in keeping inductor peak to peak current ripple constant. That would cause the frequency to shift to zero near clipping, so a lower limit has to be put. The limit is currently not well implemented as it becomes quite complex to achieve in the analog domain, but I will use a PIC with D/A for that (which I need for other duties anyway).
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