Transistor and AC

Thread Starter


Joined Jan 5, 2011
Hi everyone,

As a beginner in electronics I was following the tutorial page at about transistor amplifiers and at some point there was an explanation of how AC can pass through a transistor in active mode.

I understood that if the transistor is not in active mode the negative part of the AC waveform cannot be passed because the transistor is in cutoff then (base-emitter voltage drops bellow 0V). Also in the tutorial there is a simulation showing the signal at output which is a full AC wave.
How does the negative side of the AC waveform pass in active mode? Shouldn't the output look more like a half wave(positive) AC? I can't imagine how the output voltage could drop bellow 0V if the transistor is forward biased at all times.

Anyone could please throw some light over this concept please?


I just realized that the output voltage never drops under 0V. I was misreading the simulation graphic. But still, how can the output voltage drop bellow the bias voltage to reproduce the negative part of the input signal?

Thanks alot
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