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classd4sure 3rd February 2005 03:37 PM


You can also have intermodulation products between different channels that tend to produce annoying "whistles". That's a defect of every self-oscillating Class-D amplifier.
I wouldn't go so far as to say it's a defect, but sure it's a possibility. I understand this same problem exists in poorly implemented clock based designs as well, there's always a work around isn't there? You have to admit, the definite pro's far outweigh the possible cons.


hypnopete 3rd February 2005 11:26 PM

Does anyone know a good and reasonably simple way to set up some clipping led to a digital amplifier, ie the design i have come up with.....?? is the easiest way to use a comparator for example, when the output voltage reaches 99% of the rail voltage... any other ideas...?



classd4sure 3rd February 2005 11:32 PM

Originally I'd clamped mine at the input, two pairs of series diodes for about +-1.2 volts limiting. Later removed them I found they weren't needed in my case.


hypnopete 4th February 2005 12:26 AM

Perhaps you misunderstand.

All i want to do is give some visual indictation that clipping is occuring..



classd4sure 4th February 2005 12:31 AM

Yes I did, and that's a good idea.

How about a PLL set to lock on 150Khz :)

subwo1 4th February 2005 02:36 AM

For clipping indicators, consider two zeners, one at the upper and one at the lower rail. A resistor connects them together. The LEDS attach to the inner connections of the zeners, observing proper polarity with series 1amp 200PIV rectifiers in series with as well as the necessary current limiting resistor for each LED. The higher the voltage rating of the zeners, the farther from the rail the indicators will sense the audio signal. The LED assemblies are connected to the audio output.

hypnopete 4th February 2005 02:59 AM

Okay I'll Give that a go!!.

I think i could probably get away with just using one led, and monitoring on only one of the rails, probably the top.


subwo1 4th February 2005 06:22 AM

Sounds good.:) The rectifier should be an ultrafast or two 1N4148 in series.

phase_accurate 4th February 2005 07:24 AM

Clipping detection within class-d:

If one drives a class-d amp into clipping it stops switching. I.e. one output device is kept on and the other one off. This situation can be detected at the input of the mosfet driver by means of a retriggerable monoflop.



hypnopete 10th February 2005 11:03 AM

I have just finished winding my new Torroidal Inductor, which is for use at around 300kHz.

As i was unsure of the core material, mix. ( powdered Iron)

I set up a parallel resonant circuit with the inductor and a 1.0uF capacitor.

The resonant peak was measured at 11.5kHz.

According to my calculations, ie L=1/(((2*pi*f)^2)/C)

The inductance is 191uH!... This is much too high i beleive . There are 42 turns on the inductor.

Should i just use say 10 turns instead of 42? to get something in the ball park of 47uH?

Any help would be much appreciated. I am not sure of the exact value i need either.



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