MOSFET power dissipation calculator
Work out how much power a MOSFET dissipates: conduction loss from Rds(on), switching loss from the gate charge and frequency, and the total.
Operating point
Power loss breakdown
Conduction loss
I²·Rds(on)
Switching loss
0.5·V·I·(tr+tf)·f — (tr+tf) ≈ Qg·factor / Ig
Total dissipation
Conduction + switching
Heatsink
Parts above ~1 W need a sink
The device dissipates 1.61 W — above the ~1 W a bare package can shed, so fit a heatsink and size the junction-to-air thermal path for this power.
About the model
Conduction loss is the on-resistance times the drain current squared — Rds(on) rises roughly 50% from 25 °C to 125 °C, so use the hot datasheet value. Switching loss comes from the overlap of voltage and current during each transition; it scales linearly with switching frequency and with gate charge, and shrinks with a stronger gate driver that pushes (tr+tf) down. At high frequency switching loss usually dominates.
The model assumes hard switching with a square-wave drive and no body-diode losses, gate drive losses, or package/thermal derating. Compare against an actual circuit measurement for a production design.
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Frequently asked questions
How is MOSFET conduction loss calculated?
Conduction loss is the ohmic loss from drain current through the on-resistance: P_cond = I²·Rds(on), with Rds(on) in mΩ. With the defaults of 5 A and 50 mΩ that is 5² × 0.05 = 1.25 W. Rds(on) rises roughly 50% from 25 °C to 125 °C, so the tool expects the hot datasheet value rather than the 25 °C one.
How is MOSFET switching loss calculated?
Switching loss comes from the overlap of voltage and current during each transition: P_sw = 0.5·V·I·(tr+tf)·f, where the rise/fall time is approximated from gate charge and gate drive current as (tr+tf) ≈ Qg·factor ÷ Ig. It scales linearly with switching frequency and gate charge, and shrinks with a stronger gate driver.
When does a MOSFET need a heatsink?
The tool sums conduction and switching loss into total dissipation and says a heatsink is required above roughly 1 W, the limit a bare package can shed. It also warns when switching loss dominates — the fix is a lower-Qg part or a faster gate driver. The model assumes hard switching and ignores gate-drive and body-diode losses.
Simplified hard-switching model, Rds(on) at temperature. Real designs also budget for gate drive and body-diode losses. ICBOMS provides this tool for reference only.