Voltage Mode Pre and Post Filter Feedback

[Genomerics]

Or, in other words.... there's an extra part tagged on me website.

http://www.genomerics.org

I've been busy elsewhere but just managed to, sort of, finish off the part that has a look at Pre and Post filter voltage feedback in Class D amplifiers.

Cheers

DNA

[classd4sure]

Excellent! Certainly appreciate the examples, very useful. Can't wait for the rest. Writting style is !

[koolkid731]

Excellent tutorial.

The idealized amp shows -47db distortion for 3rd harmonic and up.

I tried w/o success higher switching freq. to reduce its distortion.

I'll recommend this to newbees.

[Genomerics]

Originally posted by classd4sure
Excellent! Certainly appreciate the examples, very useful. Can't wait for the rest. Writting style is !

Thanks! Loads of fun, I'm still learning myself.

Originally posted by koolkid731
Excellent tutorial.

The idealized amp shows -47db distortion for 3rd harmonic and up.

I tried w/o success higher switching freq. to reduce its distortion.

I'll recommend this to newbees.

It all 'depends'... I get -52dB for 1KHz 30V out. I did try reducing the deadtime and it made little difference. If you take out the clamp then it drops to -67dB. I might have to re-think that one.

Of course it's an idealised spice model but it does let you chase fundamental things.

Cheers

DNA

[koolkid731]

I did take out the clamping zeners and got -67dB 2nd HD.

This is an example of drawbacks of sawtooth-based class-D: not enough loop gain at high frequency to reduce THD.

In a self-oscillating amp, the dominant harmonic is the third when modulation index is high, with other harmonics insignificant. I'm working on reducing that 3rd HD.

[classd4sure]

Have you any plans for covering the topics of mixed feedback? It's a very non ideal solution but frequently implemented.

Seeing a current mode control design example could be interesting as well.

[Genomerics]

Originally posted by classd4sure
Have you any plans for covering the topics of mixed feedback? It's a very non ideal solution but frequently implemented.

Seeing a current mode control design example could be interesting as well.

Ahaaaa, errr not specifically mixed feedback, but you may notice that one of the sections on the front page mentions current mode control of a half bridge.

Strange to say I'm just dragging some things together to do that section. At the moment it's still a 'To Be Done'.

Cheers

DNA

[classd4sure]

aaaah .... um, did I say "could" be interesting? I meant to say "will" be..

Looking forward to it! Even more so the "new" topology.

As per mixed mode feedback, don't worry about it, it sucks anyway.

[phase_accurate]

Very nice indeed. I always wanted to put tigether soething like that but haven't found the time so far.

Regards

Charles

[Pierre]

Very nice material.

Now that Charles is here, I would like to ask how the Nyquist theorem (that we have discussed several times here) matches into the explanations exposed in the Genomerics web. He speaks about slope matching, but how does that relate to the fact that having a crossover freq. higher than Fs/2 causes inestability?

Just that I wanted to hear Charles' point of view.

Best regards,
Pierre