the applied voltage (Figure 27D). At this time, the input pulse
decays to zero and a back emf is developed across the inductor. This
voltage is equal and opposite to ER, or 63 percent of E. The
current and the resistor voltage now decrease towards zero at a rate
determined by the universal time constant chart. After 1 time
constant, the current and ER are both equal to 37 percent of the
values from which they started to decrease, or approximately 23
percent of their steadystate values. At the same time, EL is
decreasing to approximately 23 percent of E. During the next half
cycle, the current and the resistor voltage start increasing from a
value equal to approximately 23 percent of their steadystate values
and, therefore, reach a higher value than they did during the first
halfcycle when they started increasing from zero. During each
succeeding cycle, the current and the resistor voltage reach a
slightly higher value than they did during the previous cycle, until
a point is reached where ER varies equally above and below the
average value of the applied voltage (50 volts in the circuit
illustrated), and the current varies equally above and below an
average value of 50 volts divided by 100 ohms (value of R) or 0.5
amperes. The inductor voltage at this time varies equally above and
below the zero volt axis.
56
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