Switch-Mode Power Supply (SMPS) Efficiency Calculator
Compute overall efficiency of a switch-mode DC-DC converter by summing loss contributions from the MOSFET (conduction + switching), diode (forward drop + reverse recovery), inductor (DCR + core), output capacitor ESR, and controller IC bias current.
How to Use
- Enter the output power P<sub>out</sub> in watts.
- Enter estimated losses for each category: FET (conduction + switching), diode (forward drop + reverse recovery), inductor (DCR + core), cap ESR, and control IC bias.
- The calculator sums losses, adds them to P<sub>out</sub> to get input power, and reports efficiency η = P<sub>out</sub> / P<sub>in</sub>.
- The breakdown identifies the dominant loss contributor — where to focus design optimization.
Show Work
Formulas
History of SMPS Efficiency Engineering
Switch-mode power supplies trace to 1950s radar and early computer applications where high-efficiency conversion of 400 V to logic levels was essential. The first commercial SMPS for computers appeared in the late 1960s; IBM\'s System/360 mainframes pioneered line-operated switchers at scale. Early converters ran at 20 kHz (just above audible range) and achieved 70–80% efficiency.
The transition from linear to switching supplies accelerated through the 1970s–80s as cheap fast-switching bipolar and later MOSFET transistors became available. Ed Abramson and Bob Mammano\'s 1976 paper on PWM control established the design methodology; Bob Erickson and Dragan Maksimović\'s Fundamentals of Power Electronics (1999) became the definitive engineering textbook. Loss accounting — the kind this calculator does — has been standard practice since the 1970s.
Modern efficiency gains come from: synchronous rectification (replacing diodes with MOSFETs), GaN and SiC wide-bandgap semiconductors (lower switching losses), digital control loops (dynamic optimization), and active dead-time tuning. State-of-the-art converters now reach 98–99% at specific operating points — losses are approaching fundamental physical limits, and further improvements require entire topology changes (e.g., soft-switching LLC resonant converters instead of hard-switched buck/boost).
About This Calculator
Enter output power and the six main loss categories. The tool computes total loss, input power, efficiency percentage, and identifies the dominant loss contributor — pointing you to where design optimization would pay off most.
For estimated values, use these starting points: FET 1–3% of Pout, diode 1–2% (higher for non-synchronous), inductor 1–2%, cap ESR 0.3–0.8%, control bias 0.1–0.5%. Refine with datasheet specs and simulation for precise numbers. Everything runs client-side.
About the Switch-Mode Power Supply (SMPS) Efficiency Calculator
Working on electronics and circuit design? The Switch-Mode Power Supply (SMPS) Efficiency Calculator is a free browser tool that gives you the answer in seconds. Compute overall efficiency of a switch-mode DC-DC converter by summing loss contributions from the MOSFET (conduction + switching), diode (forward drop + reverse recovery), inductor (DCR + core), output capacitor ESR, and controller IC bias current.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Where do SMPS losses come from?
Five main categories: (1) MOSFET conduction loss I²·R<sub>DS(on)</sub>·D; (2) MOSFET switching loss (gate drive + overlap losses ~ V·I·t<sub>sw</sub>·f<sub>sw</sub>); (3) diode losses V<sub>f</sub>·I·(1−D) plus reverse-recovery charge Q<sub>rr</sub>·V<sub>r</sub>·f; (4) inductor losses I<sub>rms</sub>²·DCR plus core hysteresis/eddy; (5) capacitor ESR I<sub>rms</sub>²·R<sub>ESR</sub>. Adding them gives total loss.
Why does light-load efficiency drop?
Fixed losses — controller IC bias current, gate-drive power, core loss — don\'t scale down with output power. At P<sub>out</sub> = 1 W with 200 mW of fixed loss, η drops below 85% even with zero conduction loss. PFM (pulse-frequency modulation) and skip modes turn off switching between pulses to cut fixed loss at light load, raising standby efficiency dramatically.
What is 80 Plus?
A voluntary PC power supply efficiency certification program started in 2004. Basic 80 Plus requires ≥80% efficiency at 20%, 50%, and 100% load; tiers go up through Bronze, Silver, Gold, Platinum, and Titanium (≥94% at 50% load, ≥90% at 10% load). Each step costs more; Titanium is reserved for servers and enthusiast PCs.
Does efficiency vary with load?
Yes. Typical η curve: rises sharply from 0 to ~30% load, plateaus at 50–80% load (peak efficiency), drops slightly above 80% (conduction losses dominate). Design goal: make peak η fall at typical operating load, not nameplate full load.
What's the difference between synchronous and non-synchronous topologies?
Non-synchronous: passive diode for freewheeling current; diode drops V<sub>f</sub> (~0.4 V Schottky) every off-cycle. Synchronous: active MOSFET replaces the diode; drop is I·R<sub>DS(on)</sub>, often well below V<sub>f</sub>. Synchronous boosts efficiency 2–5% at high currents but adds cost and complexity (gate drive, dead-time control).
How do I use the Switch-Mode Power Supply (SMPS) Efficiency Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Buck Converter Loss Budget
Typical 5 V, 3 A buck at 500 kHz: ~0.3 W FET conduction, 0.15 W switching, 0.2 W synchronous MOSFET, 0.1 W inductor DCR, 0.05 W cap ESR = 0.8 W total loss, ~95% efficiency.
Flyback PSU Analysis
Universal-input 100 W flyback: primary FET ~2 W, secondary diode ~2 W (Schottky), transformer ~1.5 W, cap ESR ~0.5 W = ~6 W loss, ~94% efficiency. Reality is 80–88% due to higher switching-edge losses.
High-Frequency GaN Buck
GaN FETs enable 1–6 MHz switching with minimal switching losses. At 5 MHz, a 100 W GaN buck can hit 96%+ efficiency — impossible with silicon MOSFETs at the same frequency.
Data-Center 48 V to POL
Rack-level 48 V distribution feeds point-of-load regulators at CPU/GPU sockets. 48 V → 1 V conversion at 200+ A uses multi-phase interleaved bucks with 97–98% efficiency — essential for data-center energy economics.
Laptop Charger Specification
65 W USB-C PD charger typically rated at 91–93% peak efficiency. Standby losses must stay below 75 mW per DoE / EPS v2 regulations — drives micropower control IC design.
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