omfg I absolutely forgot how to do my Thev equivalent circuits...

[beer]

well, in a conceptual way, I did. I can solve the more complex ones when I do the node-voltage, solve for Vth and then close the circuit, solve for Isc and find Rth. It's very methodical and I haven't forgotten how to do that. But it's been a year since my first circuits course, so some of the theory behind the math escapes me.

I have forgotten the more basic Thevenins, i.e, when I don't think you are supposed to use node-voltage and then KCL to find Vth.

Take this example:

'A car battery provides 12.5V to a radio that can be modeled by a 6.25 ohm resistor. The same battery provides 11.7V to the headlights, modeled by a .65 ohm resistor. Find the thev equivalent for the battery.

Any help? I am aware I could go into office hours, but I'd rather not go in with such a basic question that is supposed to be review from a year ago.....I have no problem with the NEW stuff pertinent to this course, but the older stuff I forget and it will bite me in the ass, it always does.

 

[dighn]

measure open circuit Voltage that is your Vt

then find short circuit I, divide into vt and that is your Zt
or suppress independent sources (short circuit for voltage sources, open circuit for current sources) and calculate impedance

 

[beer]

Originally posted by: dighn
measure open circuit Voltage that is your Vt

then find short circuit I, divide into vt and that is your Zt
or suppress independent sources (short circuit for voltage sources, open circuit for current sources) and calculate impedance

oh sh!t thats right.

I remember the Voc/Isc graph that I drew in my notes about 10 months ago.
I just found the line equation, found the x and y ints, got Voc and Isc. Set Voc=Vth and Voc/Isc = Rth.

Thanks for reminding me. The graph clicked in my head the moment after Iread your post for some reason.

 

[Omegachi]

my god... i am doing my hw on transient response of transmission lines right now! ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

 

[beer]

Originally posted by: Omegachi
my god... i am doing my hw on transient response of transmission lines right now! ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh

Yeah.

Freshmen here take one circuits course their entire year. After that, it's every semester (or more) for the next three years, depending on your tech area. So I am in need of just refreshing myself on the basics because I got burned in diff eq on not being able to do stuff from calc I (i.e, integration by parts). I don't want to get burned my upper-div circuits courses because I can't do the basics....

Of course, I have four programming courses my first two years and then not really any after that. Kinda funny how the priorities change....

 

[Eli]

Electronics rule.

Unfortunately I don't really have much clue about what your talking about.