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Class D Switching Power Amplifiers and Power D/A conversion

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Old 22nd July 2009, 01:25 PM   #1
J.R.Freeman is offline J.R.Freeman  Canada
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Join Date: Aug 2008
Default New to Class D

Good morning all,

I'm new to class D. From what I've read so far, it sounds very interesting. I don't have any class D amplifier experience, but I do have a background in electronics so I'm hoping that might be enough to get my by on my first project. Hopefully! :P

Of particular interest to me would be a very high powered mono subwoofer amplifier. I love playing around with bigger and bigger subwoofers, however when it comes time to drive them I'm out of luck. Class D's elegant means of modulating the power supply rails lends itself well to a brute force design such as this! I have lots to learn, which means lots of questions! If anyone would like to share an opinion or suggestion, please feel free.

One question I have has to do with scale-ability. Can I take a 100 watt design and use it to modulate 1000 watts? Take the National Semiconductor LM4651 (now obsolete, but you get the idea). It's a class D driver IC, intended to be connected to an external H-bridge mosfet array.


Could I extract more power out of such a design by applying more voltage to the VCC and VEE of the mosfets, than what is applied to the LM4651? I'm assuming there is some kind of feedback path that is based on the assumption that these voltages are equal. Could I fool the LM4651 into thinking the mosfets are seeing the same supply voltages through use of a voltage divider network in the feedback path?

Also, can mosfets be ganged together somehow to increase their total current capability? Gate current is theoretically zero, so I wouldn't imagine it would be a big deal for the LM4651 to 'drive' more mosfets. However differences in Vgs while the mosfets are on may cause issues.

Finally, can you recommend any exceptional driver IC's, or power supply designs?

Thanks for looking!

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Old 22nd July 2009, 02:15 PM   #2
J.R.Freeman is offline J.R.Freeman  Canada
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Join Date: Aug 2008
Woops: I just saw the Class D Design Issues thread. I'll read up!
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