[Eeyore]

Don Pearce wrote:

Eeyore wrote:

Don Pearce wrote:

Here's the thing. Bipolar Gm is
enormously bigger than mosfet, and you can use that in an output stage.
You do it with local feedback by emitter degeneration - a fraction of an
ohm does it.

Actually NO. A fraction of an ohm isn't enough. You'd have to use about 1 ohm at least
which would be intolerable in practical designs for obvious loss reasons.


0.1 ohm is plenty in a high current stage - it makes all the difference
and brings the Gm down to a pretty flat 9ish - there isn't much to be
gained going lower. The variable resistance it is fighting is 25/(Ic *
1000). By the time you hit 200mA or so that is pretty much
inconsequential - everything above controlled by the external resistor.

Sorry 0.1 is not enough. I don't even go that low for current sharing purposes ! More like 0.15,
0.22 or even 0.33.

You're still missing the point about crossover distortion though. OK for 0.1 % THD maybe but
who's going to buy that ?

Graham