SMPS Efficiency Estimator
Estimate efficiency, losses, and heat. Use measured input/output power, or estimate from AC line values (PF-aware).
How to Use
- Pick a mode: use measured power, or estimate input from AC line values.
- Enter output voltage and current (or output power directly).
- Enter input power (measured) or AC line voltage/current + power factor.
- Check “Thermal” to estimate temperature rise from loss and °C/W.
Efficiency Lab View
Live readout: efficiency, losses, and power flow.
Eff
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Pout
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Pin
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Loss
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Risk:
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Show Work (step-by-step)
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Work is shown in base units (V, A, W) and standard AC definitions (S, P, PF) when used.
Reference
- Output power:
Pout = Vout × Iout(DC) - Efficiency:
Eff = (Pout / Pin) × 100% - Loss:
Ploss = Pin − Pout - AC apparent power:
S = Vac × Iac - AC real power:
P = S × PF - Thermal rise:
ΔT ≈ Ploss × Rθ
PF (power factor) matters for AC-input supplies when estimating real power from line current.
FAQ
Why can my wall-meter watts be different from Vac×Iac?
Because Vac×Iac is apparent power (VA). Real watts depend on power factor: P = VA×PF.
Is “loss” the same as heat?
For most SMPS, most losses end up as heat in the supply (plus a small amount as EMI/radiated energy). Treat loss as heat for estimation.
What’s a typical efficiency?
Small wall-warts may be ~80–90%. Quality supplies can exceed 90% depending on load and topology.
Why does efficiency change with load?
Fixed overhead (control/drive), switching losses, and conduction losses vary differently across load—so the curve usually peaks near mid-to-high load.
Tool Info
Last updated:
Updates may include mode improvements, unit support, and edge-case handling.