Unit 5 Day 11: RL Circuits
• Series RL Circuit Layout
• Current and Voltage Response
vs. Time when V0 is applied
• Current & Voltage Response vs. Time during circuit
discharge (Battery Removed)
A Battery Connected to an RL Circuit
• Consider a battery connected to
a series RL circuit
• The instant the switch is closed
current begins to flow and it is opposed by the EMF induced in the
inductor
• Ass the current flows, there will also be a voltage drop across
resistor R, VR=I·R (Ohm’s law), which will reduce the voltage drop
across the coil
• The current will rise gradually as more voltage is dropped across the
resistor and less across the inductor, until steady state is achieved,
in which all of the voltage drop is across the resistor
Current Response of a Series RL-Circuit
I SS
t


I  I SS 1  e 


L
 where  

R

• where  is called the time constant
RL-Circuit, Steady State, Battery Removed
• Consider the same circuit, in steady state, with the battery
removed.
I  I 0e

t

• The circuit reaches equilibrium again in approximately 4-5
