Electronics > Beginners

Why use 15V for symmetrical supply in amplifiers?

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magic:

--- Quote from: Doctorandus_P on September 26, 2021, 03:05:59 pm ---I'm not entirely sure, but I think that a higher power supply voltage results in higher linearity and thus less distortion, because the proportional biasing voltages changes are less for the same output.

--- End quote ---
You aren't wrong, and some rare opamps are officially characterized for that.

Doctorandus_P:
Thanks for the verification.
Looks like about a factor of 4 reduction of THD+N for the 17V power supply and for the same output voltage.

Somehow I expect distortion to lower with a higher power supply voltage, but noise to increase, because each electron slipping through has a higher energy.

I also find those charts suddenly stopping at 100mV instead of going through to 10mV suspicious. It always makes me wonder that something "ugly" may be happening below those 100mV and they do not want to show it. The "wavy" line of the +/- 2V5 graph is also an indication that this LM4562  has some trouble in maintaining internal biasing points at this low supply voltage.

The +/- 2V5 graph also shows a sharp clipping point at 800mV output while the +/- 17V graph shows a much rounder curve which is already starting to get worse at around 7V output. I assume this is caused by current limiting on the output.  7V / 600 Ohm is still only 12mA but apparently enough to show some non-linearity.

Edit: Oops, it's only a factor of two as "magic" wrote below, and the rising distortion can indeed have other causes too.

 

magic:
I see 2x difference. For example, 1ppm vs 2ppm at 0.8V.

Distortion is almost identical at 2kΩ so it could be input stage distortion rather than current limiting. None of it is seen at low supply because the floor is too high and hard clipping occurs earlier.

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