reverse-voltage-ramps-current-down - Electronic Circuits XIII & XIV: Power Supplies and Switching Energy Step by Step

A reverse-voltage-ramps-current-down scan holds the inductance and reverse voltage fixed and varies the interval across three rows, checking that the negative current ramp I_f = I_i + V * delta-t / L pulls current down row by row. The arithmetic is exact only for the stated voltages, times, inductances, current changes, ramp directions, and rows in the ideal inductor model. Real circuits add winding resistance, core saturation, parasitics, switching transients, probe/calibration limits, finite precision, and measurement uncertainty.

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}