power-input-current-three-row-scan - Electronic Circuits XIII & XIV: Power Supplies and Switching Energy Step by Step

Ideal converter input average current follows from output power divided by input voltage, not from a detailed switch waveform in this lesson. The power-balance rows are exact for a lossless model; real input current depends on efficiency, ripple, switch timing, inductor losses, source impedance, and measurement bandwidth.

Ideal output power rows set input-average current by conservation. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Output power sets ideal average input current

The average output voltage is accepted first. Load current then fixes output power and the ideal input-average current.

P_{\text{out}}=V_{\text{out}}I_{\text{out}}\quad;\quad I_{\text{in(avg)}}={P_{\text{out}}\over V_{\text{in}}}

Three load rows connect output power to input average current

Voltage conversion stays fixed. Increasing load current raises output power, then the same power budget sets input average current.

\begin{array}{c|c|c|c}V_{\text{out}}&I_{\text{out}}&P_{\text{out}}&I_{\text{in(avg)}}\\3\ \text{V}&1\ \text{A}&3\ \text{W}&\tfrac{1}{4}\ \text{A}\\3\ \text{V}&2\ \text{A}&6\ \text{W}&\tfrac{1}{2}\ \text{A}\\3\ \text{V}&4\ \text{A}&12\ \text{W}&1\ \text{A}\\\end{array}

The input-current row comes from the ideal power budget

The input average is not a switch waveform claim; it is the ideal power balance divided by the input voltage.

I_{\text{in(avg)}}={12\ \text{W}\over 12\ \text{V}}=1\ \text{A}