Common base amplifier exercise

  • Thread starter Rampart
  • Start date
  • #1
27
0

Homework Statement


In the following common base circuit,β=100.If Vcc=15V, VEE=4V,RE=3.3KΩ, Rc=7,1KΩ find the
Ibq and Vceq(they are related to the dc values of the Q point)

R9x3Xff.png


Homework Equations




The Attempt at a Solution


Well ah...i mainly want to ask some things.However knowing that i must show my current work,check the pdf.


I want to ask at first 2 things:
a)I believe Ibq refers to the dc base current.Now how is it possible to have Base current without a Base source.

I found Ic(=IE) but can i say that Ibq=Icq/β even if i don't have any base source?

b)Also can you please describe me the current's route?I mean Vin is in the area of the emitting diode.The ac voltage goes to The diode E.How does it move pass him,when the diode is reverse biased?

so i would like to get these things cleared out.Thanks in advance.
 

Attachments

Answers and Replies

  • #2
gneill
Mentor
20,913
2,861

The Attempt at a Solution


Well ah...i mainly want to ask some things.However knowing that i must show my current work,check the pdf.


I want to ask at first 2 things:
a)I believe Ibq refers to the dc base current.Now how is it possible to have Base current without a Base source.

I found Ic(=IE) but can i say that Ibq=Icq/β even if i don't have any base source?
Ground is a perfectly good 0 V source :) Remember that the emitter supply is negative.
b)Also can you please describe me the current's route?I mean Vin is in the area of the emitting diode.The ac voltage goes to The diode E.How does it move pass him,when the diode is reverse biased?
The AC voltage modulates the voltage at the emitter. As you might imagine, this will cause a big modulation in the base current since the base-emitter junction behaves like a typical diode where forward current changes drastically with forward bias voltage. The collector current change is even larger since it's β times the base current.
so i would like to get these things cleared out.Thanks in advance.
Hope that helps.
 
  • #3
27
0
Hope that helps.
Of course it helped sir.First thing in the morning,tomorrow,i will retry.So for now,have a good night.
 
  • #4
27
0
Ground is a perfectly good 0 V source :) Remember that the emitter supply is negative.
Ok so there is Base current.So i found it by using Ibq=IEq/(1+β).And it is around 0.0099mA.Vceq as found in the pdf is 8.6V.Was this the whole exercise?I mean i just used the DC equivalent.Am i missing something?Ibq isn't the dc base current & vceq the dc voltage?Won't they be found by using only the DC equivalent?
 
  • #5
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,072
Ok so there is Base current.So i found it by using Ibq=IEq/(1+β).And it is around 0.0099mA.Vceq as found in the pdf is 8.6V.Was this the whole exercise?I mean i just used the DC equivalent.Am i missing something?Ibq isn't the dc base current & vceq the dc voltage?Won't they be found by using only the DC equivalent?
If the question refers to the currents and voltages using upper-case letters, I and V, e.g., IBQ and VCEQ, then you are being asked to find the Q-point DC values. (Lower-case letters, i and v are, by convention, reserved for AC components due to that AC signal capacitively-coupled to the emitter.)

Your calculations match mine. :)
 
Last edited:
  • Like
Likes Rampart

Related Threads on Common base amplifier exercise

  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
14
Views
2K
Replies
3
Views
5K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
13
Views
805
  • Last Post
2
Replies
25
Views
6K
  • Last Post
Replies
1
Views
1K
Replies
17
Views
891
  • Last Post
Replies
2
Views
3K
Top