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Transistor amp question ---- not homework

P

Peter

Jan 1, 1970
0
I've posted a circuit on my webpage for everyone to view since I don't
think I should upload pictures here.

http://home.comcast.net/~bostonpeter73/


I'm trying to understand how to find Vout. Last night I played around with
loop equations, assumptions, and after hours of trying I had no luck.

The biggest part that is killing me is that 68ohm resistor up top because
you can't just say 20 volts goes to the left part and the right part of the
circuit. I know approx. what I should get because I plugged this into
MultiSim, but that's cheating in my book, I should know how to calculate
this circuit.


If anyone knows the best way to come up with the answer, please let me
know.



Thanks in advance!
 
E

ehsjr

Jan 1, 1970
0
Peter said:
I've posted a circuit on my webpage for everyone to view since I don't
think I should upload pictures here.

http://home.comcast.net/~bostonpeter73/


I'm trying to understand how to find Vout. Last night I played around with
loop equations, assumptions, and after hours of trying I had no luck.

The biggest part that is killing me is that 68ohm resistor up top because
you can't just say 20 volts goes to the left part and the right part of the
circuit. I know approx. what I should get because I plugged this into
MultiSim, but that's cheating in my book, I should know how to calculate
this circuit.


If anyone knows the best way to come up with the answer, please let me
know.



Thanks in advance!

Here's how to "sketch" it in a post, and a hint
at the bottom:


o +12
|
[R1] 68
|
+------------+
| |
[R2] 8.25K [R5] 150
| |
| e/
+-----------| Q1 2N3906
| \
| |
[R3] 36.4K +---- Vout
| |
| /
+-----------| Q2 2N3904
| e\
| |
[R4] 8.25K [R6] 150
| |
+------------+
|
Gnd

Hint: You were concerned about the left hand side and the
68 ohm resistor. What is the lowest possible voltage,
with respect to ground, at the bottom of the 68 ohm
resistor? Can you analyze the circuit, if the 68 ohm
resistor was replaced by a jumper wire?

Ed
 
P

Peter

Jan 1, 1970
0
Hint: You were concerned about the left hand side and the
68 ohm resistor. What is the lowest possible voltage,
with respect to ground, at the bottom of the 68 ohm
resistor? Can you analyze the circuit, if the 68 ohm
resistor was replaced by a jumper wire?

Ed

I believe it can be done. you pretty much ONLY have I1 on the left and I2
on the right because the emitter current of Q2 is the collector current of
Q1 and the emitter current of Q1. So it's almost a parallel circuit.
 
E

ehsjr

Jan 1, 1970
0
Peter said:
I believe it can be done. you pretty much ONLY have I1 on the left and I2
on the right because the emitter current of Q2 is the collector current of
Q1 and the emitter current of Q1. So it's almost a parallel circuit.

Ok, so what do you get (voltages) at the base of the transistors
that way? Will B-E current flow? What will happen in terms
of C-E current?

Ed
 
P

Peter

Jan 1, 1970
0
ehsjr said:
Ok, so what do you get (voltages) at the base of the transistors
that way? Will B-E current flow? What will happen in terms
of C-E current?

Ed

I think I need a few loop equations and not just pulling the 68ohm resistor
out of the circuit to make assumptions. There should be a scientific
approach to this. In any case, if I don't hear from someone soon, I'll pull
the circuit off the webpage.
 
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