how so? even without the diode, output of shown circuit still cannot reach negative voltage. transfer characteristic is not changed, all the diode does is protect transistor. in case AC input is applied

It works fine, in case u want ur signal generator to sink that current, also during that phase

 

it depends on what one uses as a signal generator. i have FG and tracking PSU that could do +/-30V and 10A. neither transistor not resistor would survive that. so statement "it works fine"only tells me that transistor was not damaged when you applied 9V sine wave from some source (your function generator).

but that is not what i am after - an answer to my question how is transfer characteristic of that circuit affected by adding the diode.

 

how so? even without the diode, output of shown circuit still cannot reach negative voltage. transfer characteristic is not changed, all the diode does is protect transistor. in case AC input is applied

So... if the input is -5 V, what is the voltage across that diode if the output still cannot reach a negative voltage?

 

it depends on what one uses as a signal generator. i have FG and tracking PSU that could do +/-30V and 10A. neither transistor not resistor would survive that. so statement "it works fine"only tells me that transistor was not damaged when you applied 9V sine wave from some source (your function generator).

but that is not what i am after - an answer to my question how is transfer characteristic of that circuit affected by adding the diode.

Here's the circuit with the diode. I've given the source an output resistance of 1 kΩ (R2).



Here's the output of the above circuit. As can clearly be seen, the output (the blue trace) is clearly going negative. With a -9 V input, we would expect the output to be about -4.2 V, which is pretty close (it's actually about -4.12 V in the sim).

 

but that is not what i am after - an answer to my question how is transfer characteristic of that circuit affected by adding the diode.

Here's the two transfer characteristics.

 

thank you for the effort, i see now what i ignored

 

Damn sneaky electrons.

I got busted good by AnalogKid a while back when I overlooked some obvious current paths.

Was embarrassing, but I learned something that day.

 

thank you for the effort, i see now what i ignored

Damn sneaky electrons.

I got busted good by AnalogKid a while back when I overlooked some obvious current paths.

Was embarrassing, but I learned something that day.

It certainly happens to all of us.

 

well... it is so obvious but i was busy at that time and did not bother to read through and think for a second - a big mistake.