Electronics > Beginners
Class B biasing
Mr Evil:
--- Quote from: mackrc1 on February 22, 2020, 07:00:40 pm ---Design a class A common emitter amplifier using a BC109 with a voltage gain of 5. Modify the bias to produce class B operation...
--- End quote ---
Maybe they mean to first bias the transistor with a current source, then replace the current source with a complementary transistor, turning it into a push-pull amplifier?
coldfiremc:
Class B stands for 180 degree conduction. So the bias must:
-Being on, only in the positive or negative hemicycle
-Have approximately 1 in voltage Amplitude gain (not mean, just when it's on).
For that, you have to turn your amplifier into a switchable current source, emitter output to minimize distortion.
mackrc1:
Its seems the circuit is meant to stay the same and the it should only conduct for 180 degrees.
I had previously tried setting the bias voltage to 550mV were the transistor is nearly fully off but with such a small input signal (100mV) the transistor is barely turning on and surley there would be a large amount of distortion as well?
Unless Im over thinking it and this is what I was meant to realise?
It seems to me that with such a small input signal it is not possible to have a true class B amplifier (where Iq = 0) at-least with the BC109.
edavid:
How do you know what the input level is supposed to be?
And yes, you are probably supposed to observe the distortion level of the class B output.
mackrc1:
The class A design wants a voltage gain of 5 with a 100mV input, then you modify the bias to class B, AB and C operation.
Sorry, I thought I had included it, I re worded it a few times before posting.
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