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Old 31st January 2008, 07:35 PM   #1
zox2003 is offline zox2003  United States
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Default Class D input LM311 Inverting input

I attached schematic of class D Amplifier.Inverting input of LM311 is connected to GND thru 2K resistor.Non-inverting pin is referencing 11K to GND.What is going on with offset in this case?
I have seen a lot of construction like this.Aren't we supposed to have capacitor in series with that 2K resistor?Maybe I am wrong...

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Old 1st February 2008, 07:48 AM   #2
Eva is offline Eva  Spain
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Offset in class D comes both from modulator DC errors and from timing errors. In self oscillating class D you can get rid of the comparator DC error by wiring it in a differential fashion. Then only the DC offset due to asymetric delay remains.

This schematic is not particularly good in that respect, as one input sees 10k at DC and 5n at HF, and the other sees 2k at DC plus 2k in series with 470p at HF.
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