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Subject: A brief stroll over the Steinmetz Bridge
NNTP-Posting-Date: Sun, 01 Dec 2002 21:38:02 GMT
Organization: AT&T Broadband
Date: Sun, 01 Dec 2002 21:38:02 GMT
This curious and elegant circuit is supposedly attributed to Charles
Proteus Steinmetz, the little dynamo of a man who pioneered the study
of ac circuits at the beginning of the twentieth century. (Looked but
couldn't find any references to it on the web.)
| L | || C |
| ,-*-. |
| ( Vac ) |
| `-.-` |
| C || | L |
| || |
| R |
Note that the L and C pairs are of equal value and that the voltage
source operates at a fixed frequency (the line frequency, for example).
Magnetically coupling the L pair will have no effect on circuit action.
Now if the capacitors and inductors are chosen such that they are
resonant at the frequency of the ideal ac voltage source then the
Steinmetz bridge circuit converts it to an ideal ac current source of
V/sqrt(L/C) at the load. A short circuit at the output presents the
input with an open circuit (think about it, the Ls and Cs are now in
parallel). If the load is removed and the output circuit goes open,
input current and output voltage will rise until something arcs over.
Very handy for driving carbon arc lamps, I suppose.
Notice that since the Steinmetz bridge is completely symmetrical, the
input and output corners of the bridge are interchangeable. In fact,
this circuit not only converts ideal source types, it functions as a
general impedance to admittance converter (but, alas, only at its
single resonant frequency).
Almost as much fun as the X converter, eh? -- analog