How to determine optimal bias class A current?
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 Chip Amps Amplifiers based on integrated circuits

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 30th August 2004, 06:21 AM #1 Sunsun22   diyAudio Member     Join Date: Jul 2004 Location: Hong Kong How to determine optimal bias class A current? I've been using resisitor to connect opamp's output stage to -V to achieve Class A operations. Yet, I have the following questions: - 1. How to determine the optimal bias current for different opamps? 2. What will happen if the current is too high? 3. What will happen if the current is too low? Thanks Sunny
 30th August 2004, 08:22 AM #2 arthur diyAudio Member   Join Date: Oct 2001 Location: . too high bias will generate heat ,or the chip die too low bias=no use
 30th August 2004, 09:49 AM #3 jan.didden   diyAudio Member     Join Date: May 2002 Location: The great city of Turnhout, BE The best way to determine it is to look at the expected output current. You want a class A current just above the max expected peak output current, so that the output stage will not cut-off. Example: Suppose your max output level is 5VRMS which is about 7V peak. Your load impedance is 1K. That means the max output current will be about 7mA. So you should bias the amp in class A say 8mA. With a supply of 15VDC that will need a resistor of just below 500 Ohms. The dissipation of your opamp now becomes 8mA from the POS supply, say of +15VDC is about 60mW (plus the 'normal' quiescent dissipation, of course, see the data sheet), which should pose no dissipation problems. Your values may be different, but that's the principle. Jan Didden __________________ Music is dither to the brain; lets me think below the usual chaos - me Get more Linear Audio for less! Check out my Autoranger and SilentSwitcher

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