How to Thevenize a Given Circuit
How to Thevenize a Given Circuit :
On the basis of Thevenin Theorem, follow the steps given below:
1. Temporarily remove the resistance (called load resistance RL) whose current is required.
2. Find the open-circuit voltage Voc which appears across the two terminals from where resistance has been removed. It is also called Thevenin voltage Vth.
3. Compute the resistance of the whose network as looked into from these two terminals after all voltage sources have been removed leaving behind their internal resistances (if any) and current sources have been replaced by open-circuit i.e. infinite resistance. It is also called Thevenin resistance Rth or Ti.
4. Replace the entire network by a single Thevenin source, whose voltage is Vth or Voc and whose internal resistance is Rth or Ri.
5. Connect RL back to its terminals from where it was previously removed.
6. Finally, calculate the current flowing through RL by using the equation,
I = Vth/(Rth + RL)
or
I = Voc/(Ri + RL)
General Instructions for Finding Thevenin Equivalent Circuit
We have considered circuits which consisted of resistors and independent current or voltage sources only. However, we often come across circuits which contain both independent and dependent sources or circuits which contain only dependent sources. Procedure for finding the value of Vth and Rth in such cases is detailed below :
(a) When Circuit Contains Both Dependent and Independent Sources
(i) The open-circuit voltage Voc is determined as usual with the sources activated or ‘alive’.
(ii) A short-circuit is applied across the terminals a and b and the value of short-circuit
current ith is found as usual.
(iii) Thevenin resistance Rth = Voc/ish. It is the same procedure as adopted for Norton’s theorem.
(b) When Circuit Contains Dependent Sources Only
(i) In this case, Voc = 0
(ii) We connect 1 A source to the terminals a and b and calculate the value of Vab.
(iii) Rth = Vab/ 1 Ω
Read article –Thevenin Theorem
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