System power budget calculator
Build a quick system power budget: add loads on each rail, choose the supply, and read total power, current draw and battery life.
Loads
0.495 W
Supply & battery
Power budget
3.3 V rail
current and power on this rail
Total power
Σ V·I across all loads
Bus current @ 5 V
total power ÷ (bus voltage × efficiency)
Battery life
capacity ÷ bus current — constant draw assumed
About the model
Every rail has a power budget and a thermal one — the amps you draw are I²R losses you have to get rid of somewhere. On a single bus, current is total power ÷ (bus voltage × efficiency), so a 12 V bus draws a quarter of the current of a 3 V bus at the same power. Battery life here assumes a constant draw: real MCUs pulse between sleep and active, so use the average current, not the peak.
Keeping rails honest? Check your voltage regulators and batteries in the catalog.
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Frequently asked questions
How is the total system power budget calculated?
Each load contributes V·I of power — entered as current (mA) or power (W) per unit times a quantity — and the tool sums them per rail and in total. A 3.3 V load drawing 150 mA adds 3.3 × 0.15 = 0.495 W, and the default first row computes exactly that.
How is battery life estimated from a power budget?
On a single bus, current is total power ÷ (bus voltage × efficiency), and battery life is capacity ÷ that current. With the defaults of a 5 V bus, 90% efficiency and a 3000 mAh cell, the estimated hours fall out directly — for example a 12 V bus draws a quarter of the current of a 3 V bus at the same power. The model assumes constant draw, so use the average current, not the peak.
How do I check that my supply is not overloaded?
The tool computes the total bus current at the chosen bus voltage and flags when it exceeds the supply current rating (default 2 A). The loads panel accepts up to five rows, each on its own rail, and every rail gets its own current-and-power line so you can spot a rail that is pulling too much and split the load or derate the supply.
Estimates only — real runtimes depend on battery chemistry and load profile. ICBOMS provides this tool for reference only.