wanna_eat_1kg_of_elecons
New Member
Hello i am new here and have got a question about emitter followers.
I am now learning about electronics and i don't care about a circuit that works like copy it from the Internet and build it, but i am more interested in HOW it works. I know it is much easier to make a buffer with a opamp but then again i want to learn how transistors work. So i found a example and want to discus what is going on.
ok here is the question i have got a emitter follower with:
A BC337 transistor.
The collector is connected to the +15V.
The emitter is connected to a resistor (Re) this resistor is also connected to the -15V.
There is a 10k resistor between the base and a functiongenerator i name it Rb, the 10k resistor is here to simulate a high impedance of a previous stage. I am not interested in that stage it could be a voltage amplifier or a sensor or a lot of things but i don't care its just there.
There are 2 situations:
situation A: Re is 3k3 and situation B: where Re is 750Ω
When i change from situation A to situation B the output voltage drops.
When i Analyze this circuit i find:
the impedance looking into the base is Hfe*Re so i think can i say:
Vout = Vin* (Hfe*Re) / ((Hfe*Re) + Rb)
Or if i ad the diode drop and the intrinsic emitter resistance re i would get:
Vout = (Vin* ((Hfe*Re) / ((Hfe*Re) + Rb +re))) -0.6v
I know a emitter follower normally follows the input signal minus 0.6V but here there is probably a voltage drop over the Rb resistor causing a voltage drop on the output and i want to get a better idea how to calculate this situation.
can anyone with more experience please tell me if my findings are correct?
I am now learning about electronics and i don't care about a circuit that works like copy it from the Internet and build it, but i am more interested in HOW it works. I know it is much easier to make a buffer with a opamp but then again i want to learn how transistors work. So i found a example and want to discus what is going on.
ok here is the question i have got a emitter follower with:
A BC337 transistor.
The collector is connected to the +15V.
The emitter is connected to a resistor (Re) this resistor is also connected to the -15V.
There is a 10k resistor between the base and a functiongenerator i name it Rb, the 10k resistor is here to simulate a high impedance of a previous stage. I am not interested in that stage it could be a voltage amplifier or a sensor or a lot of things but i don't care its just there.
There are 2 situations:
situation A: Re is 3k3 and situation B: where Re is 750Ω
When i change from situation A to situation B the output voltage drops.
When i Analyze this circuit i find:
the impedance looking into the base is Hfe*Re so i think can i say:
Vout = Vin* (Hfe*Re) / ((Hfe*Re) + Rb)
Or if i ad the diode drop and the intrinsic emitter resistance re i would get:
Vout = (Vin* ((Hfe*Re) / ((Hfe*Re) + Rb +re))) -0.6v
I know a emitter follower normally follows the input signal minus 0.6V but here there is probably a voltage drop over the Rb resistor causing a voltage drop on the output and i want to get a better idea how to calculate this situation.
can anyone with more experience please tell me if my findings are correct?