Electrical engineers please help?

Question

I need some help on sovling this problem. i have no idea how to do it. I'm totally confused and lost. here is the problem
http://img.photobucket.com/albums/v233/jster28/PRE.jpg

Answer 1

You must be more or less a beginner if you are lost so I will take the technician approach.
To get ICQ you need to find IRE (I am ignoring the current fron base to emmitter IBE as it is usually smaller than the precision)
Therefore consider IRC,ICQ IRE to be the same.
To find IRE you need the voltage across RE (VRE). VRE is almost parallell to VR2 the only difference being the VBE(active).

R1 and R2 are a voltage divider and are part of setting up your Quintescent point for the circuit. This makes the gain of the amplifier independant (around that point ) of the natural gain of the transistor.

Using a proportional approach to a voltage divider.
VR2/R2=VCC/(R1+R2)
VR2=R2*VCC/(R1+R2)
VR2=2.105V

Voltage across RE is the same less the drop VBE

VRE=VR2-0.7
VRE= 1.405

Current through RE

IRE=VRE/RE=1.405/1000= 1.405mA
IRE=IRC=ICQ
ICQ=1.405mA
watch how pedantic your teacher is on sig places!

Voltage across VRC,VCEQ,VRE must add to VCC

VCEQ=VCC-(VRC+VRE)
We dont have VRC but we know IRC as it is the same as ICEQ

VRC=ICQ*RC=4.62V

So
VCEQ=12-(4.62+1.405)=5.98V
Recheck my figures as you go through it yourself. All good engineers get someone to check after them. This will also help you to understand what I have done.

Answer 2

You need to take this problem one step at a time.

First make the Thevenin Equivalent voltage and resistance for R1 and R2. ( If you don't know what that is you had better look it up) These values will now be Rt and Vt

For a steady state DC analysis you can ignore the capacitor CE.

Now the problem is to write the equation for base current Ib and collector current, Ic as follows:

Ib = (Vt - Vbe - Re*(Ib + Ic)) / Rt

Now you know that Ic = Beta * Ib substitute and solve for Ic.

Then you can compute Vce = 12 - Re * (Ib + Ic) - Rc * Ic

Good Luck. Just work the steps and equations....