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Old 22nd June 2009, 02:48 AM   #1
Kazus is offline Kazus  Poland
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Default Class D schematic - help needed!!

Hi

Can you tell me what is wrong with this schematic! And how to correct it? This is important for me!!

Regards

Kazus

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Old 28th June 2009, 08:16 PM   #2
Kazus is offline Kazus  Poland
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Can somebody tell me, is this schem OK?! I done it but it didn't work well!! I have big distorsion in output signal! I'm not profesional constructor like you guys :P can you help me? What can I do with this circuit?!
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Old 29th June 2009, 06:49 PM   #3
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It doesn't look too good to me.

The gate drive circuits probably don't provide any dead time. T4 and T5 might limit the shoot through current, but its not a great circuit.

The time constant associated with R10 and C4 is .15 seconds. Unless I am missing something, this doesn't make sense. Also, C4 can't be a polarized cap for this application.

Is the LM566 generating a triangle (like) waveform, or what?

The base emitter junction of T1 will break down when the output of US2B goes low. This will cause degradation of its current gain.

C1 is too small for good low frequency performance.
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Old 29th June 2009, 08:16 PM   #4
Kazus is offline Kazus  Poland
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I done some photos:



This is output signal without load:
Click the image to open in full size.


Triangle waveform on pin 5 (US2B input) without load:
Click the image to open in full size. Click the image to open in full size.

Triangle waveform on pin 5 (US2B input) with load 8ohm!!!!!!!!!
Click the image to open in full size.

Input signal on top and output signal on bottom with load 8 ohm
Click the image to open in full size.

After I connect supply to the amplifier are visible noises on input & tiangle signals!!! Distorsions befor load connection ~2-3%, after load connection ~10% :/


regards
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Old 29th June 2009, 09:00 PM   #5
Pafi is offline Pafi  Hungary
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Kazus!

These pictures are horrible! Reduce their size!

Write onto every picture the V/div, and time/div settings!

I don't understand you. I don't see distortion on the output on the last picture! Where has it gone?

Those whiskers on waveforms are high freq radiations, which are collected by probe cable. You can reduce them by
- making proper ground plane on PCB,
- connecting scope probe GND to ground plane as short as possible, or in the last desperation:
- by filtering scope input.

The schematic is definitely not state-of-the art, there are some very ugly parts, but basically it works. After some proper measurements it can be tuned to work satisfactory, however this short-circuit protection is useless.

If you want to use it in full-range, L3 should be reduced.

sawreyrw!

3-4 mA reverse current wont do harm to the transistor!

Quote:
C1 is too small for good low frequency performance.
Corner freq is 1/(49000*470n*6.28)=7 Hz, so I'd say its enough.

The feedback is only for DC.

Deadtime: I'm not sure. Theoretically when T3 opens, T6 opens fast too, discharges gate of T7, and gate of T8 charged a bit slower, through 55 ohms. Maybe this is not enough, but it tries to make dead-time. Etc...
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Old 29th June 2009, 09:54 PM   #6
Kazus is offline Kazus  Poland
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My mistake, last photo concern output without load resistor!!!

Now I added new photo after connecting load resistor!!
Click the image to open in full size.

CH1 500mV/DZ CH2 5V/DZ 250us/DZ

btw.
can you tell me...
I dont know how to edit my posts?


In my previous post I have not "edit" button!! :/
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Old 29th June 2009, 10:21 PM   #7
Pafi is offline Pafi  Hungary
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The reason of distortion must be that one of the dead times (positive or negative-going) is too big. You should measure into the gate-drivers at idle to investigate it. (Or you can simply get rid of the circuit, but I think you can learn much from it, if you dig yourself into!)

Can you show us the PCB (if there is any)?

You can edit only for 30 min, but if you ask a moderator, maybe he will help you!
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Old 30th June 2009, 07:46 AM   #8
Kazus is offline Kazus  Poland
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As you wish, this is my PCB photos:

Click the image to open in full size.


Click the image to open in full size.
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Old 30th June 2009, 10:06 AM   #9
Pafi is offline Pafi  Hungary
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Just for fun: measure the voltage between the two signed points with your scope! (It should have been 0, but it's not.)

A question: do you want to use this in full-range, or only for sub? (It's unusable for full-range as it is, but can be modified.)
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Old 30th June 2009, 01:39 PM   #10
Kazus is offline Kazus  Poland
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Join Date: Mar 2009
for me better will be full-range!!
can you tell me how to modified this schem!

also I can't find other D class amplifier in discret elements!
Have you sam schematics?! or you know where I can find them!!
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