during this use decreases to zero. ER remains at 10 volts during the
remainder of the duration period.
c. At 40 usec, the applied voltage starts to decay and the
inductor opposes any change in current flow. At 41 usec, the applied
voltage has decayed to 9.5 volts. The voltage drop across the coil
is considered to be equal to the amount of decrease in applied
voltage (0.5 volt) but is opposite in polarity. The output voltage
ER, therefore, remains equal to 10 volts. The rate of current change
now becomes proportional to the rate of decrease of the applied
voltage, and the output voltage ER decreases at a rate that is equal
to the rate of decay of the applied voltage.
d. At 60 usec, the applied voltage is zero. EL has remained
constant and is equal to 0.5 volt. The output voltage ER is now
equal to EL but is opposite in polarity. The rate of current change
is considered to remain the same; and at 61 usec, there is no current
flow in the circuit and EL and the output ER are equal to zero.
29.
LONGTIME CONSTANT.
a. When the time constant is long compared to the pulse rise,
duration, and decay times, the voltage drop across the resistor is a
small fraction of the applied voltage. Most of the applied voltage
appears across the inductor and the output waveform differs greatly
from the input waveform.
b. The pulse shown in Figure 40B is applied to the lowpass RL
filter in Figure 40A. The time constant is equal to 100 usec. Since
the pulse rise time (10 usec) represents only 10 percent of 1 time
constant, the current and the output voltage ER only reach a very low
value during this time.
78
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