RC circuit
Derivation of RC transient function
RL circuit
Time constant
Application 1: relaxation oscillator
Application 2: pulse generator
Transients in DC circuits
When an RC circuit responds to a step change in input voltage, the time is takes to move 63.2% of the way to its new steady state voltage is known as the time constant, . The value of
for an RC circuit is
If the is for
, begins changing at
, and
as
, the complete transient response of the capacitor voltage is described by
For example, if and
,
Note that the significance of the 63.2% value is that .
For example, using the values of and
specified above, at time
,
The concept of a time constant can be applied to many different systems or process that exhibit exponential decay, including for example heating and cooling of a building, or radioactive decay.
The time constant of an RL circuit is