Quiescent Emitter Current Question

Thread Starter

zach7953

Joined Dec 11, 2016
7
Hi all! I'm currently working on a class A Audio amplifier. And I am messing around with my final design. I am wondering why my quiescent emitter current has to be greater than or equal to my output current. I understand that if my biasing current is not big enough, then my signal will be distorted but why? Thanks for your help!
 

Thread Starter

zach7953

Joined Dec 11, 2016
7
So what does it tell you about a "Class-A" amplifier?
"Generally class A amplifiers use the same single transistor (Bipolar, FET, IGBT, etc) connected in a common emitter configuration for both halves of the waveform with the transistor always having current flowing through it, even if it has no base signal. This means that the output stage whether using a Bipolar, MOSFET or IGBT device, is never driven fully into its cut-off or saturation regions but instead has a base biasing Q-point in the middle of its load line. Then the transistor never turns “OFF” which is one of its main disadvantages."

So what I am taking away from this is that, my signal will be distorted because if my biasing current is not large enough then it can't enter cut off or saturation?
 

MrChips

Joined Oct 2, 2009
20,880
So what I am taking away from this is that, my signal will be distorted because if my biasing current is not large enough then it can't enter cut off or saturation?
You've got that backwards. You do not want to enter saturation or cut-off.

... is never driven fully into its cut-off or saturation regions but instead has a base biasing Q-point in the middle of its load line. Then the transistor never turns “OFF” ...
 
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