|5th May 2004, 02:40 PM||#11|
Join Date: Dec 2003
Location: Near Seattle
Re: Re: Re: Biasing for different classes
Firstly, with NO bias circuitry, a push-pull BJT configuration has 2*Vbe of dead band. As I showed in my 2nd post, this is a significant portion of the wave (and therefor conduction for much less than 50%) even up to 3-watts output power. This topology does not fall into your definition of a class B ever.
Secondly, doesn't your class AB definition fall under the catagory of class A for power developed for current up to 2*bias? Where do you draw the line? At 300mA bias this is almost 3-watts of power. What if you raise the bias a bit more? Is this not a push-pull but also a class A? So what is it?
I agree there is a need to have clear definitions because these are tools we all use for discussion but since there are disparities between the authoritative sources, the only thing to do is to state your definition before your conclusion and let the readers translate to their belief system.
|5th May 2004, 05:57 PM||#12|
The one and only
"Secondly, doesn't your class AB definition fall under the catagory of class A for power developed for current up to 2*bias? Where do you draw the line? At 300mA bias this is almost 3-watts of power. What if you raise the bias a bit more? Is this not a push-pull but also a class A? So what is it?"
It's Class A up to that point, "Class B" beyond. Taken as a whole,
it's Class AB. If an amp runs Class A up to its rated power into
a particular load, it's conventionally referred to as a Class A
amp, with the understanding that beyond that output current
it's likely "B", if anything at all.
I refer to it as "B" with quotes, as someone here will argue
that it's Class AB. Subtle distinction not worth arguing about
as long as we know what we're talking about.
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