Inductor Flyback ... Back EMF

Basic modeling of inductor flyback. Use energy conservation to get "C" We assume V of spark is 4kV (measure length of spark*dielectric strength of air) E = 0.5L*i^2 Inductor Energy E = 0.5C*V^2 Capacitor Energy from spark i = 2.4Amps steady state, inductor at max L = 5mH ( like primary coil in car ignition) V = 4000V (spark into ambient air) Vs = 12 V (voltage source) R = 5ohm (like ballast resistor in car ignition) Solve C = 1.8x10-9F = 1.8nF Trick is in the sim speed. Everycircuit, as in all modeling software, can make errors. 1. Dial in max sim speed 1s/s 2. Wait for inductor voltage to reach zero (steady state) 3. Pause simulation 4. Dial down sim speed to 5us/s microseconds/sec 5. Open switch 6. You should see voltage spike -3.99kV Depending on your phone's processor you may need to dial up or down the sim speed. If voltage too large or screen skips dial up sim speed. Do not know if "ringing" is real. This is a good exercise in "calibrating" your model. Next, I plan to model a basic car ignition circuit. Target flyback voltage 200V so our "C" will increase to a typical "condensor" value used in car ignition.

published 5 years ago