reverse-voltage-ramps-current-down - Electronic Circuits XIV: Inductors and Switching Energy Step by Step

A negative inductor voltage makes a negative current change. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Negative voltage means negative current change

The initial current is 3 A. A negative voltage removes current instead of adding it.

I_f=I_i+{V\Delta t\over L}

Longer reverse time removes more current

The voltage and inductance stay fixed. Each longer interval makes the negative current change larger in magnitude.

\begin{array}{c|c|c|c|c}I_i&V&\Delta t&\Delta I&I_f\\3\ \text{A}&-2\ \text{V}&1\ \text{s}&-1\ \text{A}&2\ \text{A}\\3\ \text{A}&-2\ \text{V}&2\ \text{s}&-2\ \text{A}&1\ \text{A}\\3\ \text{A}&-2\ \text{V}&3\ \text{s}&-3\ \text{A}&0\ \text{A}\\\end{array}

Reverse voltage ramps the current down

The sign of the applied inductor voltage sets the sign of the current change; the final current is checked from the initial current.

I_f=I_i+\Delta I=3\ \text{A}+-3\ \text{A}=0\ \text{A}