MOSFET Output Capacitance Loss

P = ½ · Coss · Vds² · fsw

Quick answer

This calculator solves P = ½ × Coss × Vds² × fsw for Power Loss. With Output Capacitance 100 pF, Drain-Source Voltage 12 V, Switching Frequency 100 kHz, the result is 0.72 mW. It solves in 4 directions, so you can enter the values you have and get the one you need.

Calculator

Power Loss (mW)
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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.

Symbols and units

Symbol Meaning Default unit Accepted units
P Power Loss mW µW, mW, W, kW
Coss Output Capacitance pF pF, nF, µF, mF, F
Vds Drain-Source Voltage V pV, nV, µV, mV, V, kV
fsw Switching Frequency kHz Hz, kHz, MHz, GHz

Step by step

  1. 1. What you know: Output Capacitance 100 pF, Drain-Source Voltage 12 V, Switching Frequency 100 kHz
  2. 2. The relation: P = ½ × Coss × Vds² × fsw
  3. 3. Substitute: Coss = 100 pF, Vds = 12 V, fsw = 100 kHz
  4. 4. Result: Power Loss = 0.72 mW

Worked examples

Minimum range

Given: Output Capacitance 1 pF, Drain-Source Voltage 0.33 V, Switching Frequency 100 Hz

Result: Power Loss = 5.45 × 10⁻⁶ µW

Low range

Given: Output Capacitance 10 pF, Drain-Source Voltage 3.3 V, Switching Frequency 1 kHz

Result: Power Loss = 0.05445 µW

Typical

Given: Output Capacitance 100 pF, Drain-Source Voltage 12 V, Switching Frequency 100 kHz

Result: Power Loss = 0.72 mW

High range

Given: Output Capacitance 1 nF, Drain-Source Voltage 0.23 kV, Switching Frequency 0.5 MHz

Result: Power Loss = 13.23 W

Maximum range

Given: Output Capacitance 10 nF, Drain-Source Voltage 2.3 kV, Switching Frequency 5 MHz

Result: Power Loss = 132.3 kW

Solving for each variable

Solve for Power Loss

Output Capacitance 1 pF, Drain-Source Voltage 0.33 V, Switching Frequency 100 Hz → 5.45 × 10⁻⁶ µW

Solve for Output Capacitance

Power Loss 100 µW, Drain-Source Voltage 0.33 V, Switching Frequency 100 Hz → 18.37 µF

Solve for Drain-Source Voltage

Power Loss 100 µW, Output Capacitance 1 pF, Switching Frequency 100 Hz → 1.414 kV

Solve for Switching Frequency

Power Loss 100 µW, Output Capacitance 1 pF, Drain-Source Voltage 0.33 V → 1.837 GHz

How Power Loss changes with Output Capacitance

Output Capacitance (input) Power Loss (result)
10 pF 72 µW
25 pF 0.18 mW
50 pF 0.36 mW
75 pF 0.54 mW
100 pF 0.72 mW
150 pF 1.08 mW
0.2 nF 1.44 mW
0.4 nF 2.88 mW
0.7 nF 5.04 mW
1 nF 7.2 mW

The same result in other units

Unit Value
µW 720
mW 0.72
W 0.00072

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Frequently asked questions

How do you calculate MOSFET Output Capacitance Loss?

Use P = ½ × Coss × Vds² × fsw. With Output Capacitance 100 pF, Drain-Source Voltage 12 V, Switching Frequency 100 kHz, Power Loss works out to 0.72 mW.

What is the formula for MOSFET Output Capacitance Loss?

The formula is 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.

How do you find Output Capacitance when you know the other values?

Rearrange for Output Capacitance: with Power Loss 100 µW, Drain-Source Voltage 0.33 V, Switching Frequency 100 Hz, Output Capacitance is 18.37 µF.

How do you find Drain-Source Voltage when you know the other values?

Rearrange for Drain-Source Voltage: with Power Loss 100 µW, Output Capacitance 1 pF, Switching Frequency 100 Hz, Drain-Source Voltage is 1.414 kV.

What units does MOSFET Output Capacitance Loss use?

Power Loss is shown in µW, mW, W. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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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