# Homework Help: Help find wraparound voltage

1. Jul 17, 2011

### KrNx2Oh7

I need to find the voltage seen by the wraparound (WA) after R1, but I'm not really sure whats in parallel or series.

I think R3 is in series with R4 which are in series with the r1 and r2? If that was the case its a standard circuit problem, but not sure.

http://imageshack.us/photo/my-images/219/59571528.png/

http://imageshack.us/f/219/59571528.png/

Last edited: Jul 17, 2011
2. Jul 17, 2011

### vk6kro

If you redraw the circuit like this:

You can see the full picture.

The two voltage supplies are really grounded on their negative terminals and these ground points, and the others in the circuit, can be regarded as all joined together.

Can you see now which resistors are in parallel?

3. Jul 17, 2011

### KrNx2Oh7

Redid it with source transformatiosn

and what I get is

my original 15V source connected to R1 connected to reduced resistor lets call it Ra and a changed voltage.

Last edited: Jul 17, 2011
4. Jul 17, 2011

### vk6kro

No, the voltage sources are independent of each other. They are not in series or parallel and they affect different resistors.

You follow the path from each power supply positive output back to its negative.

Even if they share a ground connection, this does not mean they share current.

5. Jul 17, 2011

### KrNx2Oh7

step by step this is what I did.

28V/(R2+R4) is current source in parallel with (R2+R4)

reduce the resistors to R3||(R2+R4)

change it to voltage source of 28(R3||R2+R4)/(R2+R4) and the resistor is (R3||(R2+R4))

so its 15V connected to R1 connected to other resistor connected voltage source connected to ground right?

and my vout is sensed over that new calculated resistor

6. Jul 17, 2011

### KrNx2Oh7

Also I'm thinking I'm not getting the concept of ground then

Aren't all grounds connected since they all are 0.

7. Jul 17, 2011

### vk6kro

They are all connected but not because they are zero volts. The circuit would function just the same if the ground symbols were not there.

The only thing that matters is the path between the terminals of each voltage source.

For example, the 28 volt source in your problem only sends current through one resistor. Can you see which one?

8. Jul 17, 2011

### KrNx2Oh7

I see that the 28V only affects R4.

For the Vout, just to verify it is the voltage across whatever the 28V R2 R3 R4 is reduced to correct?

Was the source transformation method I did plus voltage divider afterwards not correct?

9. Jul 17, 2011

### vk6kro

What if I drew it like this:

Does that make it clearer?

I see that the 28V only affects R4.
That's right.

For the Vout, just to verify it is the voltage across whatever the 28V R2 R3 R4 is reduced to correct?

No, the 28 V supply has no effect on the output.

Was the source transformation method I did plus voltage divider afterwards not correct?
Yes, it was not correct.

10. Jul 17, 2011

### KrNx2Oh7

No current flows from the "15V circuit" to the "28V circuit" since there is no return path...so they do not affect each other like you said

So the Vout i'm looking for is the voltage drop of R3||R2 and the right side doesn't affect anything?

Also how did your first drawing with all the grounds show that there was no return path for the 28V right side circuit?
EDIT: I see it now the high side of the 28V connects to the low of R2 (ground symbol) and not high

thanks for being patient with me btw