What is the formula for MOSFET Output Capacitance Loss?

The MOSFET Output Capacitance Loss formula is P = ½ × Coss × Vds² × fsw, where P—Coss switching loss (W); Coss—Effective output capacitance (F); Vds—Drain-source voltage at turn-on (V); fsw—Switching frequency (Hz).

MOSFET Output Capacitance Loss

Q: How do you calculate MOSFET Output Capacitance Loss?

Use the formula P = ½ × Coss × Vds² × fsw. Each switching cycle, the energy stored in a MOSFET’s output capacitance (Coss) is dumped and lost when the device hard-switches on. Enter the values you know in the calculator above and it solves for the remaining variable.

P = ½ · Coss · Vds² · fsw

Calculator

Power Loss

Output Capacitance

Drain-Source Voltage

Switching Frequency

Result

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Formula

P = ½ × Coss × Vds² × fsw

Description

Each switching cycle, the energy stored in a MOSFET’s output capacitance (Coss) is dumped and lost when the device hard-switches on. This loss grows with the square of the drain voltage and linearly with frequency, so it becomes dominant in high-voltage, high-frequency hard-switched converters. It is the loss that soft-switching (ZVS) topologies are designed to recover.

Variables

P — Coss switching loss (W)
Coss — Effective output capacitance (F)
Vds — Drain-source voltage at turn-on (V)
fsw — Switching frequency (Hz)

Practical Notes

Use the energy-related effective Coss (Co(er)) from the datasheet, not the small-signal value. Zero-voltage switching reclaims this energy and is why resonant converters can run at high frequency efficiently.

Related Concepts

All Semiconductors formulas →

MOSFET Conduction Loss MOSFET Switching Loss BJT Total Dissipation Diode Power Loss Zener Regulation Resistor Transistor Current Gain (β) MOSFET Gate Drive Power MOSFET Rds(on) vs Temperature

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