i need a hand with an Electronics question

[otispunkmeyer]

how do i find the Thevenins equivalent circuit for this set up?

i know how to do it for DC circuits, but all the examples of AC thevenins theorem just have impedances in, not split up like this.

the placement of the components is screwing with me

 

[hypn0tik]

If you break the circuit along the line AB and look in, you'll see an impedance of 10 ohms in parallel with 10j ohms.
The voltage at node A is obtained by recognizing that it is a simple voltage divider, 10j/(10 + 10j)

It's been a while since I've done this, so someone please correct me if I'm wrong.

 

[OneOfTheseDays]

if your simply solving for the transfer function you don't need to use Thevenins really, a simple voltage divider will do.

 

[otispunkmeyer]

Originally posted by: Sudheer Anne
if your simply solving for the transfer function you don't need to use Thevenins really, a simple voltage divider will do.

yeah but when doing the 10+10j bit

do i just add em or do the Z = sqrt(10^2 + 10^2)

im pretty sure ive got the resistance sorted, its just the thevenins voltage i want....

10j / (10 + 10j)

what do i do with the J on the top line

 

[hypn0tik]

Originally posted by: otispunkmeyer

Originally posted by: Sudheer Anne
if your simply solving for the transfer function you don't need to use Thevenins really, a simple voltage divider will do.

yeah but when doing the 10+10j bit

do i just add em or do the Z = sqrt(10^2 + 10^2)

im pretty sure ive got the resistance sorted, its just the thevenins voltage i want....

10j / (10 + 10j)

what do i do with the J on the top line

Well, you have a j in the denominator which you want to get rid of. Rationalize the denominator by multiplying top and bottom by the complex conjugate of the denominator. Once you have all your j's in the numerator, you can write the complex number in polar form.

You'll get a result in the form A<B. When you multiply by the input voltage, your final result will be 200*A<(0+B)

 

[otispunkmeyer]

i get 141.42 volts

 

[hypn0tik]

Originally posted by: otispunkmeyer
i get 141.42 volts

There should be a phase as well.

Edit: Calculator tells me phase of 45 degrees.

 

[Qacer]

Thevenin's Theorem simply states that you can simplify a circuit into an equivalent source and equivalent load.

What do you need to find first?
- Open circuit voltage, Vab.

How do you find Vab?
- We know that two passive element in parallel have the same voltage drop across.
- We know that j10 is parallel to Zl.
- We know that we can find Vab by using voltage division.

What's next?
- Find the parallel equivalence of j10 and zl. Use the complex conjugate method or TI-89.
- Use voltage division using the parallel equivalent and 10ohms.

What's next?
- Find the Thevenin impedance.

How?
- Get rid of the voltage source by replacing it with a short circuit.
- Find the impedance seen at the point of ab. It's three elements in parallel.

 

[otispunkmeyer]

Originally posted by: hypn0tik

Originally posted by: otispunkmeyer
i get 141.42 volts

There should be a phase as well.

Edit: Calculator tells me phase of 45 degrees.

yeah sorry i get 45 too

 

[hypn0tik]

Originally posted by: otispunkmeyer

Originally posted by: hypn0tik

Originally posted by: otispunkmeyer
i get 141.42 volts

There should be a phase as well.

Edit: Calculator tells me phase of 45 degrees.

yeah sorry i get 45 too

Good stuff.