- #1

- 248

- 49

- Homework Statement
- Find the missing voltages and currents

- Relevant Equations
- Circuit analysis

Hello!

I am having trouble with this emitter circuit.

I am given U0 as well as all of the resistor values and I need to calculate the following.

## I_c## ##U_{CE} ## ## U_{C} ## ## U_{a} ## ##U_{Ca}## ##U _{Re} ## Now important to note that all of these need to be calculated at the working point of the circuit.

So since I am doing a DC analysis,I simplified the circuit and this is what I end up with

Now the Ri2 and ## U_L ## I've calculated using Thevenin circuit theorem;

$$ R_{i2} = R1||R2 $$ and $$ U_L = Uo * \frac{R2}{R1+R2} $$ ; and so far this matches the solution in the book. They simplified the circuit as well and calculated the Thevenin voltage and resistance the same way. Now I need to calculate Ib; or the base current. I used Kirchoffs law and the fact that Ic=B*Ib and I end up with this

$$ I_b = \frac{U_L-0,7}{Ri2+(B+1)Re} $$ and when I plug in the given values I get the correct answer. Plugging this Ib in the formula for Ic (as I've written it above) I get the right Ic as well, so far so good.

Now I've tried calculating Uce so the Collector-Emittter voltage and I put a loop on the right hand side of the simplified circuit and I get that

$$ U_{CE} = -U_{c} -U_{RE} + Uo $$ and to find Uc I simply used Ohm's law since I have Rc and Ic and for Ure the same, I found that the current running through Re is simply Ic+Ib and used Ohm's law. This gets me the right result as well.

Now calculating Uc gives me trouble. I simply figured it was Ohm's law but I couldnt get the right voltage. After looking at the solutions they calculated Uc like this;

$$ U_c = Uo- RcIc $$ What I don't understand why are they subracting Uo from this ? Shouldnt the voltage simply be RcIc?

Also the way they calculated ##U_{CE} ## is quite odd they calculated it like this;

$$ U_{CE} = Uo - I_c * (Rc + (1 +\frac{1}{B})Re) $$ I get the same result but why would they calculate it like this?

Also this equation is the loop equation I basically have and here the term Uc is simply resistance times voltage. Why was was Uo subtracted from this.

Thanks !

I am having trouble with this emitter circuit.

I am given U0 as well as all of the resistor values and I need to calculate the following.

## I_c## ##U_{CE} ## ## U_{C} ## ## U_{a} ## ##U_{Ca}## ##U _{Re} ## Now important to note that all of these need to be calculated at the working point of the circuit.

So since I am doing a DC analysis,I simplified the circuit and this is what I end up with

Now the Ri2 and ## U_L ## I've calculated using Thevenin circuit theorem;

$$ R_{i2} = R1||R2 $$ and $$ U_L = Uo * \frac{R2}{R1+R2} $$ ; and so far this matches the solution in the book. They simplified the circuit as well and calculated the Thevenin voltage and resistance the same way. Now I need to calculate Ib; or the base current. I used Kirchoffs law and the fact that Ic=B*Ib and I end up with this

$$ I_b = \frac{U_L-0,7}{Ri2+(B+1)Re} $$ and when I plug in the given values I get the correct answer. Plugging this Ib in the formula for Ic (as I've written it above) I get the right Ic as well, so far so good.

Now I've tried calculating Uce so the Collector-Emittter voltage and I put a loop on the right hand side of the simplified circuit and I get that

$$ U_{CE} = -U_{c} -U_{RE} + Uo $$ and to find Uc I simply used Ohm's law since I have Rc and Ic and for Ure the same, I found that the current running through Re is simply Ic+Ib and used Ohm's law. This gets me the right result as well.

Now calculating Uc gives me trouble. I simply figured it was Ohm's law but I couldnt get the right voltage. After looking at the solutions they calculated Uc like this;

$$ U_c = Uo- RcIc $$ What I don't understand why are they subracting Uo from this ? Shouldnt the voltage simply be RcIc?

Also the way they calculated ##U_{CE} ## is quite odd they calculated it like this;

$$ U_{CE} = Uo - I_c * (Rc + (1 +\frac{1}{B})Re) $$ I get the same result but why would they calculate it like this?

Also this equation is the loop equation I basically have and here the term Uc is simply resistance times voltage. Why was was Uo subtracted from this.

Thanks !