AC Electric Circuits
Suppose you had an audio impedance-matching transformer (1000 Ω to 8 Ω), and you wished to know the phase relationships of the windings. Unfortunately, the only test equipment you have is an analog DC voltmeter and a 9-volt battery. Explain how you would use these two devices to test winding “polarity.”
Note: you may disregard the center-tap of the 1000 Ω primary winding.
It should be obvious that the load voltage in this resistive voltage divider circuit will be less than 30 volts AC (RMS):
Likewise, it should be apparent that the load voltage in this inductive voltage divider circuit will be less than 30 volts AC (RMS):
From this brief analysis it would appear these two voltage divider circuits are equivalent to one another. However, there is a very important difference in terms of current: load versus supply. Estimate the load and source currents in each of these divider circuits, and comment on the difference(s) between the two.
Devices called step regulators are sometimes used in electrical power distribution systems to boost or suppress line voltages, typically to a maximum of 10%:
The “Line” side of this autotransformer is the source of power, and the “Load” side connects to those devices consuming electrical power. The “Reversing switch” alters the transformer’s function from boost to buck.
Determine which switch position is “boost” and which is “buck,” and then determine which way the moving contact (the arrow symbol) needs to be moved in order to increase the voltage output, and to decrease the voltage output.
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