Is there a problem with this Source Transformation?

AI Thread Summary
The discussion centers on a user's attempt to find the transfer function of a circuit using source transformation, resulting in a discrepancy with the expected solution. The error identified is the omission of the Thévenin impedance when representing the first stage as a voltage source, leading to an incorrect assumption of zero impedance. This oversight creates an illusion of a unity gain buffer amplifier between stages, which does not exist. To correct the analysis, the user is advised to include the Thévenin impedance to accurately reflect the loading effect. The user acknowledges the feedback and plans to adopt a cursive 's' in their work to avoid confusion in future calculations.
Danie9
Messages
2
Reaction score
0
ssadas.jpg

Hey guys, i did this source transformation as an alternate method to find the transfer function of a circuit, however I am getting a different transfer function of 2/(2s+(s+3)(s^2+1)) to the solution in the following image. Any help would be really appreciated :)
solution2.JPG
 
Last edited:
Engineering news on Phys.org
Hi danie9! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Your analysis using the first method looks right.

The mistake you're making in the second is that while representing the first stage by its Thévenin voltage source you are forgetting about its Thévenin impedance. The result is as though there exists a unity gain buffer amplifier between the two stages because you are, in effect, assuming/using a Thévenin impedance of zero ohms. But there is no such isolating amplifier. So as well as redrawing with a voltage source you need to include the impedance of that voltage source to properly account for the loading effect of stage II on stage I.
 
Last edited by a moderator:
  • Like
Likes Danie9
To avoid the likelihood of sooner or later mistaking your lower-case "s" for the numeral "5" somewhere in the middle of many pages of complex algebra, consider adopting a cursive lower-case letter "s" for your electronics work. Writing it like this will obviate one glaring opportunity for going astray in your work. (Leave off the lower-right upward flourish, that stem is needed only when joining to a following alphabet letter.)

http://www.kbteachers.com/alphabet/cursive/lowercase-s.gif ;);)
 
Last edited by a moderator:
  • Like
Likes Danie9
NascentOxygen said:
Hi danie9! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Your analysis using the first method looks right.

The mistake you're making in the second is that while representing the first stage by its Thévenin voltage source you are forgetting about its Thévenin impedance. The result is as though there exists a unity gain buffer amplifier between the two stages because you are, in effect, assuming/using a Thévenin impedance of zero ohms. But there is no such isolating amplifier. So as well as redrawing with a voltage source you need to include the impedance of that voltage source to properly account for the loading effect of stage II on stage I.
Yes thank you so much, i will definitely start using a cursive 's' :)
 
Last edited by a moderator:
Hey guys. I have a question related to electricity and alternating current. Say an alien fictional society developed electricity, and settled on a standard like 73V AC current at 46 Hz. How would appliances be designed, and what impact would the lower frequency and voltage have on transformers, wiring, TVs, computers, LEDs, motors, and heating, assuming the laws of physics and technology are the same as on Earth?
I used to be an HVAC technician. One time I had a service call in which there was no power to the thermostat. The thermostat did not have power because the fuse in the air handler was blown. The fuse in the air handler was blown because there was a low voltage short. The rubber coating on one of the thermostat wires was chewed off by a rodent. The exposed metal in the thermostat wire was touching the metal cabinet of the air handler. This was a low voltage short. This low voltage...
Thread 'Electromagnet magnetic field issue'
Hi Guys We are a bunch a mechanical engineers trying to build a simple electromagnet. Our design is based on a very similar magnet. However, our version is about 10 times less magnetic and we are wondering why. Our coil has exactly same length, same number of layers and turns. What is possibly wrong? PIN and bracket are made of iron and are in electrical contact, exactly like the reference design. Any help will be appreciated. Thanks. edit: even same wire diameter and coil was wounded by a...
Back
Top