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.

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