hello,

Quick question...

i was just wondering how the fellow in the following video got 360k for Rb????

please view 07:00 of 10:08 of the following video

http://www.youtube.com/watch?v=Pqm5-axy7m8

The math doesn't seem right....???

just wondering if its a mistake in the video.

thanks

 

It looks good to me and clearly explained by the screen at 7:13. Beta seems to be pulled out of the blue, but otherwise it's just applying Ohm's law.

 

Well, first, Rb formula seems to be a little different... As per video is it:

Rb = ((Vc - Vbb) / Ic) * 160

or does he mean:

Rb = ((Vc - Vbb) * 160) / Ic

thanks for replying wayneh
r

 

Those are the same

 

yes ... you are right

but how is the following =360k???

Rb = ((6.65 - 4.03) / 0.001) * 160

bof...... I get 419,200 !

 

yes ... you are right

but how is the following =360k???

Rb = ((6.65 - 4.03) / 0.001) * 160

bof...... I get 419,200 !

Have you tried calculating Vbb?

 

Have you tried calculating Vbb?

no, I didn't work out the problem as per se, I only
casually followed along as I was watching the video
and noticed the numbers he plugged in didn't add
up to 360k. everything else is pretty straight forwards
except the 360k ?

but off the top of my head, (3.3+0.7)?
he plugged 4.03v as vbb! no?

I guess there is something i am not seeing...
why how do you see it?

 

but how is the following =360k???

Rb = ((6.65 - 4.03) / 0.001) * 160

bof...... I get 419,200 !

Of course you are right. I can only guess he made the same error I did - ballpark the first term at 2,000 and multiply by 160.

 

okay....
thanks for replying

r