c. Response of an RL circuit. An RL circuit has the same effect
on triangular waveforms as an RC circuit if certain changes are
across the inductor in an RL circuit, and the capacitor voltage
waveform occurs across the resistor. The time constant, of course,
is equal to L/R instead of R x C. Also, when a triangular voltage
waveform is applied to an RL circuit, the current increases at a
constant rate. This constant rate of current increase, in turn,
causes the inductor voltage to become constant after 7 time constants.
Section III. HIGHPASS RC CIRCUIT
18.
GENERAL.
When ER is taken as the output voltage, the RC circuit is
known as a highpass filter. A highpass filter attenuates all
frequencies below a certain determined value, while passing
frequencies above this value.
19.
SHORTTIME CONSTANT.
a. The pulse shown in Figure 33B is applied to the highpass RC
filter in Figure 33A. The time constant of the circuit is 1 usec,
which is short compared to the rise (10 usec), duration (30 usec),
and decay (20 usec) times of the pulse. Since the time constant of
this circuit is short when compared with the pulse rise time, the
capacitor charging rate quickly reaches the rate of increase of the
applied voltage. This causes the current and, therefore, the output
voltage across the resistor to level off at a very low value.
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