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Class D Switching Power Amplifiers and Power D/A conversion

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Old 21st December 2009, 05:53 PM   #11
luka is offline luka  Slovenia
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So as it turned out, I won't have to wait until March, got 2092, and got 4227's, so I'm ready to move forward again. I will recheck everything, make sure its working
Apart from what setting for dead time to use, which I think I will have 75ns, which I hope is not that much, and not that little for fets, which are be the best I had so far.
And with freq. of about 250k, it should be up and running soon
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Old 28th December 2009, 03:15 PM   #12
luka is offline luka  Slovenia
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It works, kinda

I did expect freq. to be 250k, but with components used, (I assume I did not make any mistake), does only 93k

I will borrow this picture

Click the image to open in full size.

So based on this picture, I have
r17=1k
c12=1n
c1=c2=c4=2.2n
and R2=100 for 93k, and also tried 270 for 98kHz

Schematic is not totaly the same

I have "the same" as in Figure 26 in
http://www.irf.com/technical-info/appnotes/an-1138.pdf

One thing I also have is, limited voltage for IC, to 5.6V with zeners

What could be done? where to check for something? I hope c4 is not the problem, being 2.2n instead 1n
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Old 28th December 2009, 04:34 PM   #13
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If you are using this schematics using 4227 direct at 2092 output ,maybe this is your problem.Try using other mosfet to see if the frequency reach your target.You could also try to use a buffer and see if you get the right freq.A low qg fet can give you some answers.
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Old 28th December 2009, 05:08 PM   #14
luka is offline luka  Slovenia
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how can fets drop freq. like that? makes no sense to me. This is the best fet I could used and for that matter, only fet. I'm sure IRS can drive them just fine, since its not hot or anything. Its just about the same as ir2110, which had no problem driving stw34nb20, which has only 10nC less gate charge

you sure that C4 is not the problem here?

and gate waveforms look pretty damn good, both upper and lower

Last edited by luka; 28th December 2009 at 05:13 PM.
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Old 28th December 2009, 07:30 PM   #15
Eva is offline Eva  Spain
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If it self oscillates at 93Khz, it's because phase (plus delay) is crossing 180 degree at that frequency Check compensation and component values.
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Old 28th December 2009, 10:49 PM   #16
cccv is offline cccv  Latvia
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hello friends, if is possible i want pcb desin this amp irs2092 my email cccv@inbox.lv
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Old 29th December 2009, 08:34 AM   #17
SNY is offline SNY  Hungary
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Default help...

If it self oscillates at 93Khz, it's because missing GND ..
Check C1, C2, C4...
1nF ok. 2,2 nF ok.
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Old 29th December 2009, 09:27 AM   #18
luka is offline luka  Slovenia
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no I have gnd, that part I have, even if that schematic is wrong
C1,C2,C4 seem to be ok

after talking to Eva, which was totaly right on 2 counts, first being
Quote:
Check compensation and component values
totaly, right... changed then cap in feedback network, from 1n, to 330n and some others, and sure enough, freq. went up

2nd, this was not writen here, yet mentioned by odnaizutra is
that irs will have problems driving this fets, sure enough, this is right too
I mean it does work, but I don't think I would wan't it to run like that, without gate buffers

One thing I can say, self oscilating amp are hard to make, really, everything effect everything
But not type of fets, or better said, ther gate charge, that does not really change freq. that much, few kHz only

Still thinking what to do, do I run it a low freq, ~150k, change filter, or what... I know that I will need to change 2.7R resistor in RC filter at output, because its no good, then you have low freq, and you get +/-20v sine on output with switching freq
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Old 29th December 2009, 05:38 PM   #19
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things that can affect the switching frequency are:vbus,qg,compensation network,c1,c2,c4 and r2.Just try c1,c2 and c4 of 1kpf as the suggested schematics?
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Old 29th December 2009, 06:30 PM   #20
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anything that cause any delay will change frequency ,you can read that at some ir apps.I know that a difference at qg of that size dont really change that much the frequency,but it affect.Try to use the right capacitors at front end and r2 as suggested.I see this kind of amp as an exercise to see how different things can affect the performance of the power amplifier.In some ir apps you can also find a table of differents values of c1,c2 and c4 and r2 in order to change frequency as you wish,i am not sure an1138.Any change at this caps really matter.But all of these are just suggestions because this ic is really hard to obtain a good result at first time.
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