MOSFET Conduction Loss (RDS(on))

Estimate conduction loss using P = I² × R with RMS/DC current, duty cycle, temperature scaling, and parallel devices.

How to Use

  1. Enter RDS(on) (at a reference temperature) and choose the unit (mΩ/Ω).
  2. Enter current as DC or RMS (use RMS for pulsed/AC ripple).
  3. Set duty cycle for on-time fraction (1.0 = always on).
  4. Optionally apply temperature scaling to estimate hot RDS(on).
  5. Use Parallel MOSFETs if current is shared across multiple devices.
Loss Lab View
Conduction loss + RDS(on) hot estimate + per-device split.
RDS(on)
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I (RMS)
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P (Total)
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P / FET
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Risk: —
Duty
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N FETs
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Temp
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Tip: For PWM loads, conduction loss is based on IRMS during on-time and scaled by duty cycle.

Inputs & Settings
Enter values; results update instantly. Share links are generated only when you press Share.
Enter typical datasheet value at a reference temperature (often 25°C).
Use DC for steady current, or RMS for ripple/pulsed waveforms.
Conduction loss uses I²; RMS is correct for non-DC waveforms.
On-time fraction. 1.0 (100%) for always-on paths.
Assumes equal current sharing: I per FET ≈ I / N.
Usually 25°C if you’re using typical datasheet RDS(on).
Uses a linear coefficient: R(T) = R(ref) × (1 + α × (T − Tref)).
If unknown, try 75–125°C for warm/hot operation.
Typical ballpark: 0.003–0.006 per °C (device-dependent).
Show Work (step-by-step)
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Work is shown in base units (A, Ω, W). Duty cycle is applied as a multiplier on average power.

Reference

Conduction loss is the ohmic loss in a MOSFET channel while it is on:

  • Single device (always on): P = I² × RDS(on)
  • With duty cycle: Pavg = (I² × RDS(on)) × D
  • N in parallel (ideal sharing): Ptotal ≈ I² × RDS(on) × D / N
  • Temperature scaling (linear model): R(T) = Rref × (1 + α × (T − Tref))

This tool estimates conduction loss only. Switching loss, gate drive, dead-time body diode loss, and thermal resistances are separate effects.

FAQ

Do I use DC or RMS current?

Use RMS if the current waveform isn’t flat DC (PWM ripple, pulsed loads, AC components). Conduction loss depends on I², so RMS is the correct equivalent for varying current.

Why is hot RDS(on) higher?

MOSFET channel resistance increases with temperature. Datasheets often show RDS(on) vs. temperature; this tool uses a linear coefficient for quick estimation.

Does parallel MOSFET always split current evenly?

Not perfectly. Layout, gate drive, and device variation affect sharing. This tool assumes ideal sharing (I/N) as a first-order estimate.

Is duty cycle always correct to multiply by D?

It’s correct when your entered current represents the on-time current and you want average conduction power over the full cycle. If you already entered an overall RMS current over the full cycle, set duty to 1.0.

Tool Info

Last updated:

Updates may include unit support, waveform helpers, and edge-case handling.