Explanation of Self Oscillating Class D - diyAudio
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Old 1st October 2006, 05:01 PM   #1
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Default Explanation of Self Oscillating Class D

http://www.genomerics.org/selfosc/selfosc.html

I got bored but I'm getting better apart from it throwing up other questions so I may get worse.

Anyway, if it floats your boat there may be more to be added.


Cheers

DNA
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Old 1st October 2006, 07:37 PM   #2
IVX is offline IVX  Russian Federation
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Wrong link? Check this out.
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Old 1st October 2006, 07:38 PM   #3
Baldin is offline Baldin  Denmark
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Great work. I can only encourage you to dig deeper

What would also be very interesting is a reliable model in the frequency domain, that would enable the design of the right feedback loop (phase compensation etc.)

Have tried to make some models in Mathcad .... but I'm not sure at all if it's correct

Keep it up
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Old 2nd October 2006, 03:06 PM   #4
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Originally posted by IVX
Wrong link? Check this out.
Yes, sorry, I went to bed early and switched it off. Sort of between 8AM and 10PM GMT would be good.

I suppose I could claim I need my beauty sleep because I am pug ugly but then, since I am so ugly beauty sleep won't help too much.

It's up at the moment.

I'll drink lots of cider and leave it on overnight.


DNA
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Old 2nd October 2006, 05:42 PM   #5
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Great job. Cleared a few things up in my mind.
Very entertaining
Your whole site is great. Keep it up.
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Old 2nd October 2006, 06:18 PM   #6
BWRX is offline BWRX  United States
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That's a nice spice model to start experimenting with. Simply add a cap (say 0.68uF) in parallel to the load and a cap (say 100pF) in parallel to the feedback resistor (reduce it to something like 30k) and you've got something going.
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Old 3rd October 2006, 12:30 AM   #7
fokker is offline fokker  China
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it didn't work for me, displaying "this page cannot be displayed".

maybe it is off again?
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Old 3rd October 2006, 12:43 AM   #8
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seems to be.

DNA, any chance of hosting that stuff where it's up all the time? I think it'd be worth it.
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Old 3rd October 2006, 02:41 PM   #9
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Originally posted by Baldin

What would also be very interesting is a reliable model in the frequency domain, that would enable the design of the right feedback loop (phase compensation etc.)

Keep it up
Just got on to that bit, thought I knew a little. The result is almost alarming, I didn't expect it. Probably done something wrong but it certainly looks cute....

DNA
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Old 3rd October 2006, 03:44 PM   #10
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Self-oscillating class-d amplifiers always have enough loop gain to saturate the output stage such that effective gain forward through the amplifier and back again around the feedback loop self-adjusts to drop to unity (i.e., zero dB) exactly at the frequency where phase shift around the entire loop just reaches 360 degrees (positive feedback, unity gain).  The frequency of oscillation is controlled entirely by phase loss - gain plays no roll.  In this regard, a self-oscillating class-d amplifier is nothing more than a high level, high power phase-shift oscillator.  Setting operating frequency (and limiting its smear when producing large signal audio) is all about designing and controlling the phase shift around the loop.

An earlier diyAudio thread covered most of the pertinent details: Non clocked (e.g. free running, self oscillating) class d

Regards -- analogspiceman
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