# Help with this DTL circuit!!!!

Discussion in 'Homework Help' started by genta, Dec 1, 2008.

1. ### genta Thread Starter New Member

Dec 1, 2008
2
0
Hi!

thiis circuit is about finding the minimum HFE value

Fan-out is = 20 and the other values are in the photo below,there's missing one Rc value and it's the same Rc=1k

The hfe has to be about 11, hfe=11, but...
i solved it and I get hfe =7

what's the problem????

2. ### Papabravo Expert

Feb 24, 2006
11,946
2,561
What assumption are you making about the thresholds for a logic 1 and a logic 0. You need to take into account the beta of the transistor, the base resistance and the collector resistance none of which you have provided.

3. ### Ron H AAC Fanatic!

Apr 14, 2005
7,018
682
Look at the attached schematic.

EDIT: Hmmm, I probably should have just given some hints. I forgot this was a homework problem.

• ###### min beta.PNG
File size:
15.2 KB
Views:
20
Last edited: Dec 2, 2008
4. ### genta Thread Starter New Member

Dec 1, 2008
2
0
thank you very much Ron!!!!