
#1
Nov1707, 11:16 AM

P: 29

I'm sorry for asking again so soon, but these transistors really give my head a spin.
1. The problem statement, all variables and given/known data The problem is pretty much summed up by the following photograph: 3. The attempt at a solution To be quite honest I'm really stumped here. I can go over what I know (Or at least what I think I know): Since everything displayed here is in series, I'm presuming the current over each element is the same. The voltage over R1 should be 10  v1, basically meaning if I could find v1 I should be able to find the current R1 and thus the current in every other element connected aswell, which would make the problem easy. Vgs for the first transistor is 5 volts, and vgs=vds for the second transistor. R1 and R2 should have the same voltage drop across them. All in all, 15 volts dissipate over this circuits as vdd = 10 volts and vss = 5. After this, it completely stops. I've got the correct answer, which is v1 = 6 v and v2 = 2 v So by my logic, the current over the first resistance is (106)/1000 = 4 mA. This is where I get confused, because if v2 = 2v, doesn't that mean the voltage drop across the first transistor is 4v aswell? But if it is, this indicates that 16 mA runs through it, which isn't really possible if only 4 mA runs through the first resistance. I tried checking what the voltage vds over the first transistor had to have been in order to allow for 4mA to pass through, and as far as I can remember the answer I got was sqrt(2)+1. Which is a fairly ugly number so I'm presuming this is wrong. Anyone got a hint that can push me in the correct direction? It would be greatly appreciated. I'm dying to understand these blasted transistors. 



#2
Nov1807, 02:04 PM

Sci Advisor
PF Gold
P: 2,633

"Vgs for the first transistor is 5 volts..." Vgg=5 volts. Wouldn't Vgs=VggV2?




#3
Nov1907, 07:41 AM

P: 29

Aha, I see now, of course. Thanks!
I managed to solve it now by using four different equations, was quite a hustle but I've never figured it out if not for this! Thanks again! 


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