Question about Class D amplifier

[walker5678]

I am designing a class D audio amplifier with PWM control mode. The PWM comparator has two inputs, one is the tri-angle wave, and the other is the audio wave. My question is: how to set the swing range of the tri-angle wave? If the swing range is set to be half of the Vdd, then when the audio wave amplitude exceed the swing range of the tri-angle wave, what will happen?

thanks in advance.

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[lavitaebelle]

The peaks of the triangle wave must be equal to or greater than the peaks of the sine wave, else the audio signal amplitude will not be sensed and a low pass filter at the output will not give a faithful reproduction of the audio signal.

 

[walker5678]

Yes, lavitaebelle, it is the case. However, in order to achieve the maximum output power, the peak of audio wave should be near the Vdd and GND, then the tri-angle wave peak is also near Vdd and GND, so there is difficulties for the PWM comparator to operate at the voltage near Vdd and GND. How to solve this problem? Thanks!

 

[Btrend]

in class-D , Duty*VCC is the gain of ur output signal , not the modulation amplitude, but keep the input amplitude < Vpeak of sawthooth waveform...
it does not matter what Vpeak u choose.... it only care about what Duty result..

 

[walker5678]

keep the input amplitude < Vpeak of sawthooth waveform...

Does it mean that the preamplifier gain should be adjusted to be compatible with the peak to peak range of the sawtooth wave? For example, if the overall gain of class D amplifier is 1, and the sawtooth wave range is from 0.25Vdd to 0.75Vdd, so the value of R2/R1 should be 1/2, is it right?

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[Btrend]

keep Vin*(R2/R1) < 0.5Vdd is necessary.