Class D principle

112

01:02:18

Just something I'm trying to put together 

published 6 years ago

hurz

6 years ago

you see this ringing again and again, its because the PWM stops for clipping at analoge to digital conversation. If PWM starts after a little pause the LC part does ring for a while.

thebugger

6 years ago

Yes, I'm trying to get around that. Not sure how exactly though. The advanced feedback seems to counteract the effect slightly, but still needs work

hurz

6 years ago

lower the input peak voltage to 1.5V or maybe 1.6V

hurz

6 years ago

another mean would be to change the LC filters

thebugger

6 years ago

Any proposition for the LC filters.

hurz

6 years ago

yes, 30uH and 470nF for 8Ohm load. corner frequency is about 40kHz and dumpening is perect for 8Ohm. Ringing depends on the ohmic load. For 16 and 4 i have to recalculate. Or do it yourself?

thebugger

6 years ago

Hmm, isn't 40kHz a bit high. Then the filtering would be affected

thebugger

6 years ago

There is considerable ringing with 30uH 470nF with a simulated speaker.

thebugger

6 years ago

Not that 42uH/2.6uF doesn't have huge ringing as well

hurz

6 years ago

40kHz is needed to not have to bad phase shift at 20kHz. With 200kHz you are five times above that corner, ok for a second order filter to not be radio transmitter from loudspeaker cabel, for nothing else we do that filtering, to get an elctromagnetic emmission stamp. 30uH 470nF for which speaker resistance?

hurz

6 years ago

sorry, this combi 470n 30u is for 16 Ohm, and is with 8 Ohm as i said earlier underdamped (series dampening), hmm i will check tomorrow. you have the formulas check them against what my mind reminds d=R/2√(C/L) while d=1 for critical in series resonator, well set d=1 and solve for R is 1/R=1/2√(C/L) with 470n and 30u we then get about 16 Ohm. ugly, but im doing that from mind in this comment field and not on a piece of paper from better wiki or lab-book information. please check if 16 Ohm is now correct and what is your loudspeaker impedance/only resuistance

thebugger

6 years ago

I was testing it out with 2mH inductance 8ohm resistance. I'll check with a 16ohm load now. But a 16ohm load would actually be 32ohms, right? As it is bridge connected

hurz

6 years ago

which combi does result into 2mH, which formula have you used?

thebugger

6 years ago

I just figured that'd be a reasonable speaker inductance.

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