Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

BJT Biasing Formulas

Status
Not open for further replies.

ABEL DANIEL

Member level 2
Joined
Apr 10, 2012
Messages
47
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
1,594
IMG_20141114_104639.jpg



For this i have have a SOLUTION.But i have a doubt in the solution:
Here,base current is found by applying KVL to i/p loop and then

Then Ic =βIb and then Ie=gamma Ib=(β+1)Ib
So Rc is found by applying KVL to output loop

My question is, can we apply formulas like Ic=alpha* Ie(like one,that we used here),Ic=βIb and Ie=gamma*Ib,blindly in every problem;dont we need to find the region of operation(active,cutoff and sat)first,before applying these formulas?
 
Last edited:

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
18,920
Helped
4,209
Reputation
8,421
Reaction score
4,152
Trophy points
113
Activity points
124,366
Hi,

My hint: What goes in must come out. Ib and Ic goes in, Ie goes out. ==> Ie = Ib + Ic.

Klaus
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,959
Helped
14,145
Reputation
28,549
Reaction score
12,831
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,225
dont we need to find the region of operation(active,cutoff and sat)first,before applying these formulas?
Yes, you do. In the present example, the transistor is in saturation, thus beta isn't valid.
 

peeyushsigma

Member level 4
Joined
Apr 15, 2012
Messages
76
Helped
19
Reputation
38
Reaction score
17
Trophy points
1,288
Location
Bengaluru, Karnataka, India
Activity points
1,755
you can not apply these formulas blindly ...here is some points to remember...

1. firstly suppose transistor is in active region and find out the base current.
2. apply Ic =βIb.
3. find Icsat= (Vcc-0.2)/Rc.
4. If Ic< Icsat. then Transistor is in active region otherwise if Ic>=Icsat then it is in saturation region.
 
Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top