RL Time Constant Calculator
RL Time Constant (τ)
Calculate τ = L / R
Current at Time t
Calculate inductor current during energizing: I(t) = (V/R) × (1 - e^(-t/τ))
Formula
τ = L / R | I(t) = (V/R) × (1 - e^(-t/τ)) [energizing] | I(t) = I₀ × e^(-t/τ) [de-energizing] | fc = R / (2πL)
Frequently Asked Questions
What is an RL time constant?
The RL time constant (τ = L/R) is the time it takes for the current through an inductor to reach approximately 63.2% of its final steady-state value. After 5τ, the current is considered to have reached its maximum value (99.3%).
How does an RL circuit differ from an RC circuit?
In an RC circuit, voltage across the capacitor rises exponentially (τ = RC). In an RL circuit, current through the inductor rises exponentially (τ = L/R). Capacitors oppose voltage changes while inductors oppose current changes.
What happens when an RL circuit is de-energized?
When the voltage source is removed, the inductor tries to maintain current flow, producing a voltage spike (back-EMF). The current decays exponentially: I(t) = I₀ × e^(-t/τ). This is why flyback diodes are used with inductive loads.
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