MM0704, Lesson 1
When the applied voltage is below the resonant frequency of the LC circuit, the circuit reactance is inductive.
When the applied voltage is above the resonant frequency of the LC circuit, the circuit reactance is capacitive.
(where R is negligible).
Time Constants and Transience
Transience is that period during which there is a rapid change from one steady state to another. An example is the
current through a capacitor after a voltage is applied to it.
The study of time constants concerns itself chiefly with the study of any electric circuit during its DC transient periods.
Although a square wave may be AC, each half cycle may be considered a temporary DC voltage. Time constants
involve nonsinusoidal waves such as square waves, triangular waves, and spiked waves.
In the study of circuits it is vital to know how the size of capacitors, resistors, and inductors, along with the frequency,
will determine the rate of the change in the transient wave.
Review of Simple Circuits
Review the following before starting the detailed explanation of time constants.
EL = IXL,
The resistance (R) is the factor that, if multiplied by the current (I), establishes the voltage across a resistance.
The L Circuit. The expression for the voltage across an inductor is
EL = IXL,
where XL = 2fL.
The RC Circuit. The expression for the sum
of the voltage drops
of the circuit shown
in figure 1-12