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Old 3rd December 2007, 04:30 AM   #11
zox2003 is offline zox2003  United States
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Ohhh..I fogot.I did play aroun with gate resistor value (currently is 10 ohms) .I increased it and nothing got changed.I also have a dead time RCD network on input of IR2010 (100ohms and 470p).I needed to pull out t 470pF caps because amp did not want to work at all with cap or would make like a dumps in speaker when I aplied audio.So currently there is just 100ohm in parallel with diode(1N4148) on input of IR2010.

Any clue what is going on?
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Old 3rd December 2007, 08:19 AM   #12
Eva is offline Eva  Spain
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If you have access to an oscilloscope and plenty of big $$$ equipment (like you said), why are you neither talking about waveforms at all or publishing pictutes of them to help us find the problem?

Otherwise, if you can't even borrow an oscilloscope, why are you telling us those fairy tales about RF engineering and big $$$$ companies? I was very serious when I told you to get one handy.

Is an RF engineering method to check whether the 12V regulator and the gate driver IC are getting hot in order to know if the amplifier is working properly??? This sounds like a joke. You don't even seem to know the self oscillation frequency that you have got, which is probably higher than expected.

You won't be able to find out what is going wrong and fix it until you can take a detailed look at waveforms. I already told you...
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Old 3rd December 2007, 10:55 AM   #13
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Old 4th December 2007, 03:26 AM   #14
zox2003 is offline zox2003  United States
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Here are soe pictures:

output
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File Type: jpg output 360khz re.jpg (18.5 KB, 1233 views)
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Old 4th December 2007, 03:28 AM   #15
zox2003 is offline zox2003  United States
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Gate on FET (+ rail):
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Old 4th December 2007, 03:30 AM   #16
zox2003 is offline zox2003  United States
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FET gate (on - rail) -reference to GND
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Old 4th December 2007, 03:33 AM   #17
zox2003 is offline zox2003  United States
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Input of IR2010 (ref to GND).All previous mesurements are referencing to GND also: What is wrong with amplifier?
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Old 4th December 2007, 04:42 AM   #18
Eva is offline Eva  Spain
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Ouch, you have massive ringing and it's on every oscilloscope measurement, so there is a strong common-mode and radiated component. If this is the no-load no-signal behaviour, then you are likely to have strong cross-conduction.

The ringing characteristic is inherent to the PCB layout and placement of decoupling capacitors, but it should not be excited in such a strong way when the amplifier is idle. You should not have any cross-conduction with IR2010 because it has 30ns of built-in dead time, but this amount of ringing indeed tells that you have. I think something is wrong with gate drive.

Some ideas:
Check the two inputs of the IR2010 against overlapping.

Try 1k and 220pF RCDs at the input of the IR2010 (don't put the diodes reversed!), this will probably introduce enough dead time to avoid cross-conduction. I think that you had trouble with 100 ohms and 470pF because it was too low R and too high C. Try a higher value gate resistor, like 100 ohms, with a turn-off diode in parallel (if you weren't doing it that way already), slower turn-on will result in less ringing excitation...

Check gate drive for amount of overlapping: Don't connect the supply rails, fed the IR2010 and the CD4069 with an aux. supply, use a signal generator to apply 300Khz sq. wave to the input of the CD4069 (as if it came from the LM311). Join the sources of both IRF540 and take a look at the gates in dual trace mode...

Note that I have not checked your schematics or your layout in detail, so I may be missing some obvious mistake...

BTW: If you do more oscilloscope pictures, try to make them more detailed, like the ones that I posted. The edges are the interesting part of the signals and should be "zoomed", while there is nothing interesting in the flat portions. Showing several signal periods is also of little interest when they are all the same. Also, try to use dual trace mode to show, for example, Vg-s against Vd-s, or input to the IR2010 against Vg-s, etc...
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Old 4th December 2007, 01:44 PM   #19
zox2003 is offline zox2003  United States
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There ia a 4 ohm dummy load on output and no input signal.

Thanks for help EVA.When you said do not put diodes reversed-did you think of not putting diodes at all or "be carrefull do not put them reversed put them right way".

Why gate signals are not looking same?
Is 78M12 OK to supply IR2010 and CD4069?It does get hot.Should I replace it with transistor and zener diode (faster for peaks)?
My output FET's are also getting really hot.

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Old 4th December 2007, 07:51 PM   #20
Eva is offline Eva  Spain
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Oh, didn't you know that gate driving draws substantial current?

Didn't you make any calculations about the exact current requirements for your MOSFETs and switching frequency? This is a must in order to know beforehand the amount of heat produced in the regulator.

Multiply gate charge at your gate drive voltage by switching frequency and by two and you will have an estimation of average gate driver current consumption.

If we take 60nC and 400Khz we get approx. 50mA. Multiply this by the voltage being dropped by the regulator and you get the amount of heat. This is very elementary electronics. If you have 32V in and 12V out, you get 20*.05=1W loss in the regulator. Remember that maximum input for 78xx/79xx is 35V. 1W may be too much for a SMD package.

Concerning the diodes, I meant that you should place them in the right direction.

Concerning MOSFETs getting hot, this is an obvious symptom of cross-conduction.
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