# LR circuit for PWM Input

#### electronicsLearner77

Jul 2, 2015
306
If i give a pwm signal for the LR circuit with 50% duty cycle, during on the ON time the current will increase and during the OFF time does the current decreases and reverses its direction during the OFF period or it only decreases. My question is mainly on why the current does not reverse?

#### crutschow

May 7, 2021
763
My question is mainly on why the current does not reverse?
And my question is, why do you think it would reverse?
What do you understand about inductance and how inductors behave, that would lead you to think the current would reverse in your circuit?

It would need a voltage source in the reverse direction to reverse the current.
That can occur in an LC resonant circuit, where the capacitor generates the reverse voltage as part of the resonant oscillation, but there is no capacitor in your circuit for that to happen.

Last edited:

Moderator
Nov 17, 2011
13,336
Do the math:
VL = L × di/dt.
VR = R × i
V1 = VR + VL

#### bidrohini

Feb 1, 2023
152
Here is a video series about RL circuit step-by -step design and analysis. You can watch this too:

Feb 19, 2021
623
You thinking of this :

As you can see coil polarity reverses when diode shuts off.

Regards, Dana.

#### electronicsLearner77

Jul 2, 2015
306
Thank you all for the answers, it is always confusing how many times i read, understood for now that current only decreases does not reverse. The initial thought was when voltage signal is applied the current increases in the inductor, and during the OFF period the inductor had to discharge the energy and assumed it will send through the resistor in the opposite direction.

#### electronicsLearner77

Jul 2, 2015
306
One other clarification is
Initiating the storage phase for the inductor L by closing switch

instant the switch is opened.
Now i ask main question in the above diagram there is also ground and it was always told ground is the low resistance path, then current shall go to ground without passing through resistance R2, but why it does not happen? I am confused with ground path.

#### crutschow

May 7, 2021
763
I am confused with ground path.
You have a common misconception about ground.
Ground/common is just the usual name for a node in the circuit that is used as a 0V reference point for all the other circuit voltages (since all voltages are referenced between two nodes).
It has no other special characteristic.
Obviously no current can go in or out of that node symbol unless the ground has more than one connection (where would it go?) which, in your circuit, it does not.

#### crutschow

May 7, 2021
763
during the OFF period the inductor had to discharge the energy and assumed it will send through the resistor in the opposite direction.
The mechanical analogy of inductance is inertia.
The inductance tries to keep the current flowing in the same direction until the inductive stored energy is dissipated.
That can cause the voltage across the inductor to reverse, but that just serves to slow down the current, not reverse it.

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