Nodal Analysis - Electronic Circuits Projects Diagrams Free

petesmc · 18th November 2004, 01:05 AM

Hi,

I'm having problems getting the right answer for the nodal voltages of the included circuit. They should be -4/3 V for Va and 4V for Vb, but i just can't get these. Can someone write a follow through of how to find these nodal voltages for me?

Thanks
-Peter

evandude · 18th November 2004, 01:42 AM

are you getting the following two simultaneous equations?

a/4+3+(a-b)/2=0

(b-a)/2+b/3-4=0

solving those gives -4/3 for a and 4 for b.

petesmc · 18th November 2004, 01:50 AM

I get -3 and +4 for the currents in each of the equations instead of 3 and -4. I thought current away is negative and current into is positive?

-Peter

evandude · 18th November 2004, 01:57 AM

you can do it either way, the signs will work themselves out. i did it with out of the node positive.

if you do it into the node positive, then you would have to negate ALL those terms, in which case all the negative signs would drop out anyway. sounds like you are getting the signs wrong for the current in the terms other than the current sources.

for instance, a/4 refers to the current going OUT of the node a. to get the current into the node you would have to use -a/4.

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18th November 2004, 01:42 AM	(permalink)
evandude	are you getting the following two simultaneous equations? a/4+3+(a-b)/2=0 (b-a)/2+b/3-4=0 solving those gives -4/3 for a and 4 for b.

18th November 2004, 01:50 AM	(permalink)
petesmc	I get -3 and +4 for the currents in each of the equations instead of 3 and -4. I thought current away is negative and current into is positive? -Peter

18th November 2004, 01:57 AM	(permalink)
evandude	you can do it either way, the signs will work themselves out. i did it with out of the node positive. if you do it into the node positive, then you would have to negate ALL those terms, in which case all the negative signs would drop out anyway. sounds like you are getting the signs wrong for the current in the terms other than the current sources. for instance, a/4 refers to the current going OUT of the node a. to get the current into the node you would have to use -a/4.