# beta dc

Discussion in 'Homework Help' started by amaresh92, Jan 1, 2011.

1. ### amaresh92 Thread Starter New Member

Oct 31, 2010
23
0
calculate alpha DC (emitter to collector dc current gain) and beta DC (base to collector dc curent gain) for a transistor which has Ic=2.5ma, Ie=2.6ma .

formula 1) alpha DC=Ic/Ie.
formula 2) beta DC =Ic/Ib.
formula 3) beta DC = alpha DC/(1-alpha DC)
formula 4) Ib=Ie-Ic

alpha dc=Ic/Ie

=2.5/2.6
=0.96

Ib=Ie-Ic

=2.6-2.5
=0.1ma

using formula 2)

beta DC =Ic/Ib

=2.5/0.1
=25

using formula 3)

beta DC = alpha DC/(1-alpha DC)

= 0.96/(1-0.96)

=24

my doubt is, from above calculation for beta DC using formula 2 and 3 we are getting two different values for beta DC. so which one is correct and under which condition or how i should use these two formula? In the sense when i should use formula 2 and formula 3.

2. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
203
You should be posting in the homework forum - correct?

3. ### mik3 Senior Member

Feb 4, 2008
4,846
70
You should get the same answer. If you round beta DC to 5 decimal places you will get the same answer.

4. ### amaresh92 Thread Starter New Member

Oct 31, 2010
23
0
i am really beg pardon for my blunder mr. marshallf3.
hence after it would not be repeated.

5. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
I think it's a problem with alpha rounding, not with beta rounding. Beta is 25.0000, so rounding isn't an issue.