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Old 4th December 2004, 08:55 AM   #1
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Default Feedback in Clocked H-Bridge

Hi All,
I'm currently working on a Class D amp based around the HIP4080. I've simulated the triangle wave generator and it works fine (opamp type) and currently have it simulating with no feedback.
My question is how do I do the feedback from a H bridge?

Is is as simple as say a difference and and a resistor to the input? (probably not )

As its my first attempt, I'm only aiming to use it as Subwoofer amplifier. If it worked in a kind of linear fashion between 20-100Hz I would be very happy.

Also, how am I able to simulate the H bridge in Pspice when the HIP4080 doesn't have a model?

Many Thanks
Matt
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Old 4th December 2004, 11:06 AM   #2
tiki is offline tiki  Germany
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Hi,

even if it is a hard work, try to find out some hints concerning your project out of this thread.
Many people did good work here, including simulation, generator designs, drivers, dead time issues, e.t.c. (e.g. JohnW wrote a lot of interesting posts, which may contain some worthy solutions for your work).
IMHO are the timing characteristics of the generator, comparator and driver sections etremely urgent for the sound quality, also for the low frequency range, if you start without feedback.

IVX realised an interesting small design already (with HIP 4080, as I remember).
I did use HIP 2100/2101 for the driver, they are faster and more flexible therefore, with the small disadvantage of lower driving capability.

A first start for a "differential" feedback may be the Mueta version .

Good luck,
Timo
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Old 7th December 2004, 03:47 AM   #3
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Schematic -
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Old 7th December 2004, 03:55 AM   #4
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Code:
 HARMONIC   FREQUENCY    FOURIER    NORMALIZED    PHASE        NORMALIZED
    NO         (HZ)     COMPONENT    COMPONENT    (DEG)       PHASE (DEG)

     1     1.000E+03    3.382E+01    1.000E+00   -2.586E+00    0.000E+00
     2     2.000E+03    2.915E-04    8.619E-06    9.727E+01    1.024E+02
     3     3.000E+03    2.311E-02    6.833E-04   -1.788E+02   -1.710E+02
     4     4.000E+03    8.774E-05    2.594E-06   -1.532E+01   -4.975E+00
     5     5.000E+03    2.584E-03    7.638E-05   -1.794E+02   -1.664E+02
     6     6.000E+03    1.018E-04    3.010E-06   -1.028E+02   -8.727E+01
     7     7.000E+03    2.803E-04    8.287E-06   -1.466E+02   -1.285E+02
     8     8.000E+03    2.408E-04    7.120E-06   -9.688E+01   -7.620E+01
     9     9.000E+03    1.105E-04    3.268E-06   -9.084E+01   -6.757E+01
    10     1.000E+04    1.825E-04    5.397E-06   -6.560E+01   -3.974E+01


     TOTAL HARMONIC DISTORTION =   6.877638E-02 PERCENT
I went through a few class D threads (the one you mentioned helped greatly) and came up with this design. I havn't incorperated the H bridge yet but the half bridge results are looking good sofare!!

0.068% THD if I measured it right. I thought it was pretty good for my first attempt

The only problem I'm having is the gain. For a 33v output I have a 2v input off +- 100v rails. When I try to increase the gain, the distortion goes up and the output has a few defects near the top of the wave.
If anyone else sees anything that can be improved please comment.

Many Thanks
Matt
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Old 9th December 2004, 12:45 PM   #5
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Smile Reply

Hi Frost,
See this schematic, i think it can provide you with a good idea.

regards,
ampman
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Old 9th December 2004, 01:16 PM   #6
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OP-AMPS in the feedback path is what we want to avoid. Please make the forward path symmetrical and keep the feedback purely passive.

Regards

Charles
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Old 9th December 2004, 02:15 PM   #7
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hi Charles nice to see you

yeah , i think opamps must be avoided,
One can also use two seperate modules with switching frequency in phase and audio signal outpof phase, so that switching frequency will cancel out and audio will pass through , thus eliminate the need of difference opamp in feedback.

Regards
ampman
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