DC Circuits
INDUCTANCE
The relationship between values of current reached and the time it takes to reach them is called
a time constant. The time constant for an inductor is defined as the time required for the current
either to increase to 63.2 percent of its maximum value or to decrease by 63.2 percent of its
maximum value (Figure 7).
Figure 7 Time Constant
The value of the time constant is directly proportional to the inductance and inversely
proportional to the resistance. If these two values are known, the time constant can be found
using Equation (3-5).
(3-5)
TL
L
R
where
TL =
time constant (seconds)
L
=
inductance (henries)
R =
resistance (ohms)
Rev. 0
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