Home › Lessons › Transients › RL transient

RL transient

Transients · Intermediate · about 15 minutes · part of Zen’s Electronics Design Mastery

An inductor resists changes in current. Switched on, the current rises exponentially with τ = L/R. Switched off, the stored energy keeps it flowing through the flyback diode.

RL transient: the circuit on the simulator's bench

Open this lesson in the labFree, in your browser, no account needed.

How it works

τ = L / (R + Rcoil) = 10 H / 140 Ω = 71.4 ms

I(t) = If + (I0 − If) · e−t/τ, with If = Vs / (R + Rcoil) = 71.43 mA

The scope's yellow trace is VR = I · R, so it draws the current.

Try it on the bench

  1. Click S on and watch the current ramp up on the scope (yellow).
  2. Click S off. The diode lets the coil current die away instead of arcing. Remove the diode and try again to see the kick.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Capacitors, Inductors & Time”.

More on transients