# i have problems solving transistor and AOP excercices

#### haythem

Joined Oct 15, 2016
4
hello and thanks for helping
first problém its says write the equation of current IL flowing from RL on this differential AOP (i know how to solve basic AOP)
second help me to wriite the equation of gain=s/e of this NPN transistor and also how to calculate the gain when T=25C and Vcc=12V
thank you so much

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#### WBahn

Joined Mar 31, 2012
30,301
So... are you going to show ANY attempt at solving YOUR homework problems?

Or is your idea of "help" having someone just work your homework for you?

#### haythem

Joined Oct 15, 2016
4
well i know only how to solve basic differential aop with superposition law, i have never tried to solve current equation.
any way im electrical engineer specialized on high voltege and renuable energy not on electronics

#### WBahn

Joined Mar 31, 2012
30,301
In other words, you don't feel you should even be expected to try.

#### haythem

Joined Oct 15, 2016
4
hi sir, well for transistor i found the solution now im trying for the differential amplifier
basic solution is like that:
S=(R2/R1).(e2-e1)
to find the IL current flowing from RL
i use voltage divider law as S=R2.IL+RL.IL <=> IL=S/(R2+RL)
what do you thing sir about my responce and thank you

#### haythem

Joined Oct 15, 2016
4
In other words, you don't feel you should even be expected to try.
hi sir, well for transistor i found the solution now im trying for the differential amplifier
basic solution is like that:
S=(R2/R1).(e2-e1)
to find the IL current flowing from RL
i use voltage divider law as S=R2.IL+RL.IL <=> IL=S/(R2+RL)
what do you thing sir about my responce and thank you

#### DGElder

Joined Apr 3, 2016
351
S=(R2/R1).(e2-e1)
to find the IL current flowing from RL
i use voltage divider law as S=R2.IL+RL.IL <=> IL=S/(R2+RL)
what do you thing sir about my responce and thank you

haythem,

To get help in this forum you need to show your work. Just magically showing a solution without supporting math does not cut it.
Your answer is incorrect but we can't show you where you went wrong if you don't show each of the steps to your solution.
This "AOP" circuit is a differential voltage to current converter, i.e. the current in RL is independent of RL.

If you are at a loss knowing where to start, you might start with applying KCL for the noide at the top of RL; and voltage addition, starting at e1, to get the voltage at S - taking advantage of the properties of an ideal op amp of course.

Last edited:

#### DGElder

Joined Apr 3, 2016
351
Well, over a week with no closure so I am closing it out with an answer. IL = (e2-e1)/R1. I solved for a more general case, but when it got messy, I got lazy and just solved for the original problem where R3=R2.

#### MichaelNorton

Joined Oct 25, 2016
1
haythem,

Can you reply to last post from DGElder? he decided your problem?

So... are you going to show ANY attempt at solving YOUR homework problems?

Or is your idea of "help" having someone just work your homework for you?
These students usually go directly to the math problems and start working them without any preparation. When they get stuck on one problem, they flip to the back of the text for the answer. Then, they either try to work the problem backward, to understand the problem steps, or they just copy down the answer. =)