From: Chuck Simmons
Organization: You jest.
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Subject: Re: Choosing the right transformer
Date: Sun, 19 Jan 2003 19:00:45 GMT
NNTP-Posting-Date: Sun, 19 Jan 2003 11:00:45 PST
> I am not quite sure i get the whole feedback idea... Why would we try to
> close the loop around the modulator? That does not make any sense to me.
> The actual "amplifier" is the class D analog circuit (the H bridge), if
> there are any feedback to be put in this design, shouldn't it be between the
> output of the H bridge and the input of the H bridge, NOT the input of the
> modulator. Or am i just missing something?
> "Chuck Simmons" wrote in message
> > Greg wrote:
> > >
> > > > ** Normally the supply voltage ( with all its ripple) is fed into
> > > > feedback loop to correct for this problem - is there no way you can do
> > > this
> > > > ?
> > >
> > > The modulator is implemented in a dsp so I don't see how the supply
> > > could be fed back...
> > >
> > > Greg
> > It is clumsy and expensive but it can be done with an A/D converter for
> > the feedback. After all, the most common use of DSP's is probably
> > feedback systems. Most of these applications, though, are 10 or 12 bit
> > and not suited to audio. Oh, the feedback would be from the filtered
> > output rather than the power supply (technically, using the power supply
> > voltage to correct is called anticipation or feed forward).
The H-bridge is like a logic gate in this case. When the supply varies,
what is going into it is already wrong so it must be corrected. That can
only be done in the modulator. In other words, the feedback must be to
the last element which contains a linear representation of the signal.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org