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Class D Switching Power Amplifiers and Power D/A conversion

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Old 19th April 2007, 06:41 PM   #391
blmn is offline blmn  Brazil
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Im not at home now. In a few hours Ill take some shots and put them here.

But the behaviour is like in this picture:
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Old 19th April 2007, 07:01 PM   #392
luka is offline luka  Slovenia
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Hi

What schematic did you use?
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Old 19th April 2007, 07:04 PM   #393
BWRX is offline BWRX  United States
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What do the switching and high side gate drive waveforms look like?
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Old 20th April 2007, 06:17 AM   #394
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Hi everyone !

I got the same problem of noise at the top of the sinus wave with my proto

clock design @ 250kHz with IR2113 driver +2*IRFP4227
it occurs at 40Vpeak when driving 4 ohms
I'm using T106-2 core 47uH + 470nF MKP
rail voltage are +/- 80V
see pic...

could someone help ?
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Old 20th April 2007, 08:18 AM   #395
luka is offline luka  Slovenia
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Hi

I think that fredos said that you have to use big upper capacitance and lower too, but most important is as he wrote
Quote:
good 0.47uF 250V MKT will cure all ringing you have on your squared wave! Some 0.1uF ceramic with 4.7 ohms resistor to ground help a lot too...
0.47uF is cap that is connecteb between +V and -V as close to fets as possible.

And there is something that you gave ground plane under inductor, wich will increase winding capacitance and eliminate ringing.

I hope that this is right
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Old 20th April 2007, 01:50 PM   #396
blmn is offline blmn  Brazil
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Hi,

I took some shots of the waveform yesterday and, after some measurements, I notice that the problem has to do with the layout and absence of some decoupling caps, like Fredos said.

After some wiring mods the ringing was reduced and the amp easily swings more than 90vpp at 8ohms.

At this weekend I wil improve the wiring and will put some decoupling caps. after that I will try o achieve near full rail swing.

for an old analog audio guy its a very funny challenge to put this amp to work...

Tks all
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Old 20th April 2007, 03:35 PM   #397
luka is offline luka  Slovenia
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Hi

Looks good. What is your supply voltage? If you don't get good decoupling cap, buy one that has high voltage, ie. 630v. What happens if you go more than 90Vpp?
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Old 20th April 2007, 05:41 PM   #398
blmn is offline blmn  Brazil
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Luka,

The power supply voltage is 70V regulated in half bridge SMPS.

Its able to put out more than 90vpp, but I prefer rewire and decouple the circuit before stress it.

by the way, actually I just forgot to glue the output coupled inductor of the power supply and the buzz of it when the current raises at 1kHz is awful. I will test more excursion after gluing that too...

best regards

Here is other picture of it working with 35vdc at 1kHz. No problems and a clean waveform.
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Old 20th April 2007, 05:49 PM   #399
luka is offline luka  Slovenia
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Hi

Looks great, could you send me more info on smps and pic if you have them. Did you synchronize it with amp?
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Old 20th April 2007, 06:11 PM   #400
blmn is offline blmn  Brazil
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I will take more shots and put them here.

The power supply is a half-bridge design using a SG3525 controller at 65kHz and 4 irfp450 feeding a toroidal transformer. Its not syncronized.

I designed it to supply aprox. 1.5kW at output, but it was my first off-line design and for sure there is room for some improvement. Im planning use a PFC stage in order to reduce the bulk capacitors at input, a real PITA to reduce the dimensions of the power supply at these levels of power.

The sum of power supply ripple and the amp ripple at voltage buses is really a mess...Im planning to clean it too. I dont know how, yet...

Below is the picture of the waveform at 20kHz 35vdc. 10v/division at output.

Best regards,
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