The problem ask for Thevenin Equivalent for the circuit attached.
Vth = Vab
Rth = Req
Rth = Vth / Isc
Rth = 1 / It
The Attempt at a Solution
Already calculated Vth = 166.67 V. I've no problem with that. Already confirmed by textbook answer.
However, my issue is with Rth,
As per book there 3 methods to calculate Rth
1st Method : Kill independent sources and Rth = Req as seen by terminals. (Provided all sources in the circuit are independent).
2nd Method : Make a wire (short circuit) between a & b going from a to b. Calculate current of this wire (Isc), Req = Vth / Isc
3rd Method : Kill independent source, Put test voltage source with value 1 V, Put test current (It) going from - to + , calculate current, Rth = 1 / It
For the attached circuit, 1st method cannot be used as there is dependent source in the circuit.
I used third method and got Rth = 10 ohm, which is the correct answer.
My issue with the 2nd method !!
If i used the second method and make short circuit between a & b, 10 ohm will be removed as it is parallel with short circuit. Then i calculate Isc and it is zero ! i used different methods (kcl kvl, mesh) still zero!
which will make Rth = 166.67 / 0 = infinity! which wrong for sure. Answer should be Rth = 10 ohm
My questions are :
(1) Did i summarize the methods correctly?
(2) Why is Isc = 0 when I use the second method?
Thanks in advance.
16.2 KB Views: 261