Regulator Waste Current Limit Three-Row Scan - Electronic Circuits XIII & XIV: Power Supplies and Switching Energy Step by Step

The load current turns a regulator voltage drop into heat, so each row checks whether the waste power stays inside the thermal budget. The arithmetic is exact only for the stated input voltage, output voltage, load current, ideal regulator behavior, and fixed power limit; real supplies add dropout variation, thermal resistance, current-limit foldback, tolerance, cooling, and voltage/current/temperature measurement uncertainty.

Load current turns the same voltage drop into a waste-power limit 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 waste row

Input and output stay 7 V and 5 V. Load current 1 A makes waste 2 W against a 4 W budget, so margin is 2 W.

P_w=2\ \text{W},\quad m=2\ \text{W}

2 A waste row

Input and output stay 7 V and 5 V. Load current 2 A makes waste 4 W against a 4 W budget, so margin is 0 W.

P_w=4\ \text{W},\quad m=0\ \text{W}

3 A waste row

Input and output stay 7 V and 5 V. Load current 3 A makes waste 6 W against a 4 W budget, so margin is negative 2 W.

P_w=6\ \text{W},\quad m=-2\ \text{W}