Class D schematic - help needed!!

Kazus · 22nd June 2009, 02:48 AM

Hi

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

Regards

Kazus

Kazus · 28th June 2009, 08:16 PM

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?!

sawreyrw · 29th June 2009, 06:49 PM

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.

Kazus · 29th June 2009, 08:16 PM

I done some photos:

This is output signal without load:

Triangle waveform on pin 5 (US2B input) without load:

Triangle waveform on pin 5 (US2B input) with load 8ohm!!!!!!!!!

Input signal on top and output signal on bottom with load 8 ohm

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

Pafi · 29th June 2009, 09:00 PM

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...

Kazus · 29th June 2009, 09:54 PM

My mistake, last photo concern output without load resistor!!!

Now I added new photo after connecting load resistor!!

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!! :/

Pafi · 29th June 2009, 10:21 PM

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!

Kazus · 30th June 2009, 07:46 AM

As you wish, this is my PCB photos:

Pafi · 30th June 2009, 10:06 AM

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.)

Kazus · 30th June 2009, 01:39 PM

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!!

22nd June 2009, 02:48 AM	#1
Kazus diyAudio Member Join Date: Mar 2009	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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28th June 2009, 08:16 PM	#2
Kazus diyAudio Member Join Date: Mar 2009	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?!

29th June 2009, 06:49 PM	#3
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	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.

29th June 2009, 08:16 PM	#4
Kazus diyAudio Member Join Date: Mar 2009	I done some photos: This is output signal without load: Triangle waveform on pin 5 (US2B input) without load: Triangle waveform on pin 5 (US2B input) with load 8ohm!!!!!!!!! Input signal on top and output signal on bottom with load 8 ohm 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

29th June 2009, 09:54 PM	#6
Kazus diyAudio Member Join Date: Mar 2009	My mistake, last photo concern output without load resistor!!! Now I added new photo after connecting load resistor!! 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!! :/

29th June 2009, 10:21 PM	#7
Pafi diyAudio Member Join Date: May 2004 Location: Budapest	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!

30th June 2009, 07:46 AM	#8
Kazus diyAudio Member Join Date: Mar 2009	As you wish, this is my PCB photos:

30th June 2009, 01:39 PM	#10
Kazus diyAudio Member 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!!