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Using Thevenin's theorem on Wheatstone Bridge
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 Author Topic: Using Thevenin's theorem on Wheatstone Bridge  (Read 1104 times)
V8meathead
Jr. Member

Posts: 51

 « on: August 23, 2006, 01:01:18 AM »

What's the correct way to use Thevenin's theorem to find the current going through Rs?  I keep getting 5mA and it should be 3.33mA.  I can't figure out where my problem is.
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indulis
Electronics God

Posts: 651

 « Reply #1 on: August 23, 2006, 11:53:52 AM »

Does it have to be with Thevenin's? Try it with a "delta-Y" transformation..........

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V8meathead
Jr. Member

Posts: 51

 « Reply #2 on: August 29, 2006, 09:16:58 PM »

V8meathead, I know what you're doing wrong:

When using Thevenin to determine the current through Rs, you need to find an equivalent thevenin source for the rest of the circuit (the red block), this consists of Vth & Rth. For that you need to figure out the open circuit voltage & short circuit current at the terminals of Rs. 5mA is the SC current; it's not your final answer! Find the thevenin parameters as above & replace the red block with the thevenin equivalent source, then calculate the current through Rs, it is 3.3mA.

Ref: Nilsson & Riedel, Electric Circuits 6th edition 2001

Ah ha!  Thanks, I appreciate it.
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