4-40
from a long time constant (10 times the pulse duration), a short time constant (1/10 of the pulse duration),
and a medium time constant (that time constant between the long and the short). To accurately plot values
for the capacitor output voltage, we will use the Universal Time Constant Chart shown in figure 4-34.
Figure 4-34.—Universal Time Constant Chart.
You already know that capacitor charge follows the shape of the curve shown in figure 4-34. This
curve may be used to determine the amount of voltage across either component in the series RC circuit.
As long as the time constant or a fractional part of the time constant is known, the voltage across either
component may be determined.
Short Time-Constant Integrator
In figure 4-35, a 100-microsecond pulse at an amplitude of 100 volts is applied to the circuit. The
circuit is composed of the, 0.01µF capacitor and the variable resistor, R. The square wave applied is a
pure square wave. The resistance of the variable resistor is set at a value of 1,000 ohms. The time constant
of the circuit is given by the equation:
TC = RC
Substituting values:
T = 1,000 · 0.01µF
T = (1
103) · (1
-8)
