Charles, we need your help on feedback in single supply Class-D - diyAudio
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Old 23rd December 2004, 12:26 PM   #1
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Arrow Charles, we need your help on feedback in single supply Class-D

Hi Charles,

I want to use the Clocked version of Class-D amp in Single Supply mode. But my confusion is regarding feedback network, i want to use feedback from before filter and to inverting input of comparator. there is no level shifting though. So what would be a good scheme to connect the feedback, is it possible or not.
Reply soon.
Sincere regards,
kanwar
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Old 23rd December 2004, 01:21 PM   #2
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NFB from before the filter is usually done with a summing integrator. Since these are "inverting" you'd have to swap the inputs of your comparator.
But for heaven's sake ,what do you want to use this for (i.e. single supply) ? As a voice-coil cooker ?

Regards

Charles
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Old 23rd December 2004, 01:25 PM   #3
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Old 23rd December 2004, 02:56 PM   #4
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Arrow ThanX Charles

Quote:
Originally posted by phase_accurate
NFB from before the filter is usually done with a summing integrator. Since these are "inverting" you'd have to swap the inputs of your comparator.
But for heaven's sake ,what do you want to use this for (i.e. single supply) ? As a voice-coil cooker ?

Regards

Charles
SALUTE Charles,

ThanX for the Help.

Can we Swap the inputs of IR2110 instead , I mean to say Hi and Lo inputs swapping. is it possible. If not , than would I have to add another opamp as summing integerator for this, is there will be an DC offset Problem asscociated with single supply feedback.
kindly advise us.

No, we dont want to cook Voice- Coil, I simply want to use these 2 modules in Bridging topology , there is no cooking indeed.

Sincere Regards,
kanwar
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Old 27th December 2004, 06:16 AM   #5
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You can of course change phase by swapping the input control signals.
Between the lines I somehow feel that you wanted to use the comparator as integrator to avoid another op-amp. You definitely can't do this for several reasons.
So you will definitely need another op-amp for the integrator. There would also be a possibility for doing this just passively. But apart from simplicity I don't see any advantages of doing so.

There is no offset problem if everything is properly referenced to the same "ground", which is not the negative supply rail but an "artificial" at half the supply voltage.

Regards

Charles
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Old 28th December 2004, 05:12 PM   #6
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Quote:
Originally posted by phase_accurate
You can of course change phase by swapping the input control signals.
Between the lines I somehow feel that you wanted to use the comparator as integrator to avoid another op-amp. You definitely can't do this for several reasons.
So you will definitely need another op-amp for the integrator. There would also be a possibility for doing this just passively. But apart from simplicity I don't see any advantages of doing so.

There is no offset problem if everything is properly referenced to the same "ground", which is not the negative supply rail but an "artificial" at half the supply voltage.

Regards

Charles
Hi Charles ,
ThanX for your Advise,

So what will be your suggesstion:
1) using an extra opamp

or

2) Swapping the control inputs.

We want to use control signal swapping as these can contribute lot more to simplicity.

Advise us, so that we can move further.

Regards,
kanwar
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Old 29th December 2004, 07:47 AM   #7
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Hi Kanwar

You seem to be a multiple personality !

Quote:
So what will be your suggesstion:
1) using an extra opamp

or

2) Swapping the control inputs.
I am afraid you don't have a choice of either one or the other. You'd have to do both. You will have to use a summing integrator for your feedback (alternatively you can use the same integrator for both NFB and triangle generation).
And you will have to change the phase of the PWM signal by either:
1.) swapping the comparator inputs or
2.) swapping the fixed H and L signals on the 2nd XOR inputs or
3.) swapping the mosfet driver's control inputs.

Regards

Charles
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Old 29th December 2004, 12:01 PM   #8
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Arrow reply

Here is the figure
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Old 29th December 2004, 12:02 PM   #9
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Arrow Still Confusing

hi Charles nice advise , but still under confusion.

I want to use a carrier based Class-D approach.

therefore , I will take LM6172 as Triangle generator.
According to my understanding about what you have said is that the triangle generator can be used as both for feedback and integerator, Am I right if not then correct me. than what about comparator.

regards,
kanwar
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Old 30th December 2004, 06:24 AM   #10
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The circuit as shown would not work. You would need a summing integrator. You could do this to a ceratin degree by connecting a capacitor from the inverting input of the comparator to signal ground. But this would be suboptimal.

If you use the opamp as triangle generator directly then you can't use it as integrator as well at the same time (though I have to do some thinking about that) but you could use an opamp as a self-oscillating class-d modulator directly (i.e. hysteresis modulator).

If you want to generate the triangle by integrating a rectangular, then you can use the integrator for the NFB as well at the same time (like the old Sony patent).

But you will definitely need to add something to your schematic !

Regards

Charles
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