A question about classD

[incol]

Why classD need feedback, I think it can also work without feedback. What the concept of the classD feedback, Does anyone have the some files about this? I am a new deslgner about classD, thanks very much!!

 

[sethtalk]

it can improve PSRR, THD+N performance,
for example, the feedback resistor RF in fig5
()
sense the average duty cycle and compare to the current
in R2 ,and then send the error signal (current) to
the integrator to adjust the PWM edge ,then the power suppy reduced error compensated!
but, the psrr=0 dB is open loop design! got it?

 

[incol]

it can improve PSRR, THD+N performance,
for example, the feedback resistor RF in fig5
()
sense the average duty cycle and compare to the current
in R2 ,and then send the error signal (current) to
the integrator to adjust the PWM edge ,then the power suppy reduced error compensated!
but, the psrr=0 dB is open loop design! got it?

Hi sethtalk,

Thank you very much. But I don't know "the psrr=0 dB is open loop design! ", what does it mean?

 

[freezeover]

PSRR=0 means the output of your Class-D amplifier changes as much as its power supply changes. as PSRR is an important specification in power amplifier, so you have to feedback.

 

[sethtalk]

sorry;
"the psrr=0 dB is open loop design! " should be
"the psrr=0 dB in open loop design! "


remember , class-d output stage operation means
output node switch to power (or ground ) through
a switch ,which have zero impedence ideally,
so, any signal (noise) on power line will couple
to output node directly,hence psrr=0 dB.
hope to help you!!