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| SEC. 1-1 THE THREE KINDS OF
FORMULAS A definition is a formula invented for a new concept. A law is a formula for a relation in nature. A derivation is a formula produced with mathematics. SEC. 1-2 APPROXIMATIONS Approximations are widely used in industry. The ideal approximation is useful for troubleshooting. The second approximation is useful for preliminary circuit calculations. Higher approximations are used with computers. SEC. 1-3 VOLTAGE SOURCES An ideal voltage source has no internal resistance. The second approximation of a voltage source has an internal resistance in series with the source. A stiff voltage source is defined as one whose internal resistance is less than 1/100 of the load resistance. SEC. 1-4 CURRENT SOURCES An ideal current source has an infinite internal resistance. The second approximation of a current source has a large internal resistance in parallel with the source. A stiff current source is defined as one whose internal resistance is more than 100 times the load resistance. SEC. 1-5 THEVENIN’S THEOREM The Thevenin voltage is defined as the voltage across an open load. The Thevenin resistance is defined as the resistance an ohmmeter would measure with an open load and all sources reduced to zero. Thevenin proved that a Thevenin equivalent circuit will produce the same load current as any other circuit with sources and linear resistances. SEC. 1-6 NORTON’S THEOREM The Norton resistance equals the Thevenin resistance. The Norton current equals the load current when the load is shorted. Norton proved that a Norton equivalent circuit produces the same load voltage as any other circuit with sources and linear resistances. Norton current equals Thevenin voltage divided by Thevenin resistance. SEC. 1-7 TROUBLESHOOTING The most common troubles are shorts, opens, and intermittent troubles. A short always has zero voltage across it; the current through a short must be calculated by examining the rest of the circuit. An open always has zero current through it; the voltage across an open must be calculated by examining the rest of the circuit. An intermittent trouble is an on-again, off-again trouble that requires patient and logical troubleshooting to isolate it. |