# The Art of Electronics - SINGLE ENDED FOLLOWER AMPLIFIER (pg.91)

#### vol_

Joined Dec 2, 2015
93
Yes, we are one edge of saturation.

There is nothing wrong in saturation, but in saturation BJT loses all his current gain which is not good for our amplifier. But you probably know this already.
Cheers for one more time!
Cheers!

#### vol_

Joined Dec 2, 2015
93
View attachment 100883

At the peak Q1 is Cut-off
Why Q1 is cut off? I'm getting (with Vb2=13V), Ve1=13V > Vb1=12,4V > Vc1=-30V.

#### Jony130

Joined Feb 17, 2009
5,180
It is a common practice to assume that Q1 is OFF (stage before the output stage) if we want to find the peak output voltage. Because as the load current increases, Q2 needs more base current and this base current is provide by this 100mA current source. So, if Ib2 = 100mA there is no current left for Q1.
And this is why Q1 will or I should say may it be cut-off. It's all depend on load Vin and Q2 beta. Remember hfe =50 and hfe = 70?

#### vol_

Joined Dec 2, 2015
93
It is a common practice to assume that Q1 is OFF (stage before the output stage) if we want to find the peak output voltage. Because as the load current increases, Q2 needs more base current and this base current is provide by this 100mA current source. So, if Ib2 = 100mA there is no current left for Q1.
And this is why Q1 will or I should say may it be cut-off. It's all depend on load Vin and Q2 beta. Remember hfe =50 and hfe = 70?
OK. But if Q1 is cut off no signal will pass 'through' it, isn't it? So how can we have an output voltage peak while we dont have an input voltage?

#### Jony130

Joined Feb 17, 2009
5,180
OK. But if Q1 is cut off no signal will pass 'through' it, isn't it?
Yes indeed and this is why this voltage will give us a information about clipping/the output peak positive swing.