Input Average Current Budget Three-Row Scan - Electronic Circuits XIII & XIV: Power Supplies and Switching Energy Step by Step

An input-average-current budget turns the output load demand into the average input current a buck source must supply. The current margins are exact only for the declared output voltage, load current, input voltage, and ideal lossless conversion model; real supplies include ripple, finite efficiency, switch and diode drops, inductor winding resistance, ESR, saturation, thermal drift, and voltage/current measurement uncertainty.

Output load current is converted into an input-average current budget check. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

1 A load row

Buck output stays 3 V. Load current 1 A asks for input average 1/4 A against a 1/2 A budget, so margin is 1/4 A.

I_{\text{in}}=\tfrac{1}{4}\ \text{A},\quad m=\tfrac{1}{4}\ \text{A}\Rightarrow\text{pass}

2 A load row

Buck output stays 3 V. Load current 2 A asks for input average 1/2 A against a 1/2 A budget, so margin is 0 A.

I_{\text{in}}=\tfrac{1}{2}\ \text{A},\quad m=0\ \text{A}\Rightarrow\text{pass}

3 A load row

Buck output stays 3 V. Load current 3 A asks for input average 3/4 A against a 1/2 A budget, so margin is negative 1/4 A.

I_{\text{in}}=\tfrac{3}{4}\ \text{A},\quad m=\tfrac{-1}{4}\ \text{A}\Rightarrow\text{fail}