Switching Loss (Power Context)

Psw = 0.5 × V × I × (tr + tf) × f

Quick answer

This calculator solves P_sw = ½ × V × I × (t_r + t_f) × f_sw for Switching Loss. With Drain Voltage 12 V, Drain Current 2 A, Rise Time 10 ns, Fall Time 22 ns, Switching Frequency 100 kHz, the result is 38.4 mW.

Calculator

Result
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Formula

P_sw = ½ × V × I × (t_r + t_f) × f_sw

Description

Switching loss occurs during the transition periods when the MOSFET or IGBT is neither fully on nor fully off. During these transitions, the switch simultaneously has voltage across it and current through it, dissipating energy. Each switching event (turn-on and turn-off) contributes roughly ½ × V × I × transition_time of energy loss. Multiplying by the switching frequency gives the average power dissipated. Switching loss is the dominant loss mechanism at high frequencies and drives the trade-off between switching frequency (size, cost) and efficiency.

Variables

  • P_sw — Average switching power loss (W)
  • V — Voltage across the switch during off-state (V)
  • I — Current through the switch during on-state (A)
  • t_r — Turn-on rise time (s)
  • t_f — Turn-off fall time (s)
  • f — Switching frequency (Hz)

Practical Notes

This linear approximation is accurate for hard-switched converters. Soft-switching (ZVS, ZCS) techniques can reduce switching loss to near zero. GaN FETs have tr + tf of 5-20 ns compared to 30-100 ns for silicon, enabling higher frequencies at lower loss. Gate drive strength directly affects switching speed: faster gate drive = shorter transition time = lower switching loss but higher EMI.

Symbols and units

Symbol Meaning Default unit Accepted units
Psw Switching Loss W µW, mW, W, kW
V Drain Voltage V pV, nV, µV, mV, V, kV
I Drain Current A pA, nA, µA, mA, A, kA
tr Rise Time ns ps, ns, µs, ms, s, min, h
tf Fall Time ns ps, ns, µs, ms, s, min, h
f Switching Frequency kHz Hz, kHz, MHz, GHz

Step by step

  1. 1. What you know: Drain Voltage 12 V, Drain Current 2 A, Rise Time 10 ns, Fall Time 22 ns, Switching Frequency 100 kHz
  2. 2. The relation: P_sw = ½ × V × I × (t_r + t_f) × f_sw
  3. 3. Substitute: V = 12 V, I = 2 A, tr = 10 ns, tf = 22 ns, f = 100 kHz
  4. 4. Result: Switching Loss = 38.4 mW

Related quantities from the same inputs

  • P = V × I = 24 W

Worked examples

Minimum range

Given: Drain Voltage 0.33 V, Drain Current 2 mA, Rise Time 100 ps, Fall Time 0.22 ns, Switching Frequency 100 Hz

Result: Switching Loss = 1.06 × 10⁻⁵ µW

Low range

Given: Drain Voltage 3.3 V, Drain Current 20 mA, Rise Time 1 ns, Fall Time 2.2 ns, Switching Frequency 1 kHz

Result: Switching Loss = 0.1056 µW

Typical

Given: Drain Voltage 12 V, Drain Current 2 A, Rise Time 10 ns, Fall Time 22 ns, Switching Frequency 100 kHz

Result: Switching Loss = 38.4 mW

High range

Given: Drain Voltage 0.23 kV, Drain Current 100 A, Rise Time 100 ns, Fall Time 0.22 µs, Switching Frequency 0.5 MHz

Result: Switching Loss = 1.84 kW

Maximum range

Given: Drain Voltage 2.3 kV, Drain Current 1 kA, Rise Time 1 µs, Fall Time 2.2 µs, Switching Frequency 5 MHz

Result: Switching Loss = 18400 kW

How Switching Loss changes with Drain Voltage

Drain Voltage (input) Switching Loss (result)
1.2 V 3.84 mW
3 V 9.6 mW
6 V 19.2 mW
9 V 28.8 mW
12 V 38.4 mW
18 V 57.6 mW
24 V 76.8 mW
48 V 153.6 mW
84 V 0.2688 W
120 V 0.384 W

The same result in other units

Unit Value
µW 38400
mW 38.4
W 0.0384

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Frequently asked questions

How do you calculate Switching Loss (Power Context)?

Use P_sw = ½ × V × I × (t_r + t_f) × f_sw. With Drain Voltage 12 V, Drain Current 2 A, Rise Time 10 ns, Fall Time 22 ns, Switching Frequency 100 kHz, Switching Loss works out to 38.4 mW.

What is the formula for Switching Loss (Power Context)?

The formula is P_sw = ½ × V × I × (t_r + t_f) × f_sw. Switching loss occurs during the transition periods when the MOSFET or IGBT is neither fully on nor fully off.

What units does Switching Loss (Power Context) use?

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

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