MOSFET Conduction Loss
P = I² × Rds(on)
Quick answer
This calculator solves P = I² × Rds(on) for Power. With Drain Current 2 A, Rds(on) 50 mΩ, the result is 0.2 W. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
When a MOSFET is fully turned on, it behaves like a small resistor (Rds_on) between drain and source. The power dissipated during conduction follows the I-squared-R relationship. Modern power MOSFETs have Rds_on values ranging from milliohms to hundreds of milliohms depending on voltage rating and die size. Lower Rds_on means less conduction loss but typically comes with higher gate charge and switching losses. Conduction losses dominate at low switching frequencies, while switching losses dominate at high frequencies.
Variables
- P — Conduction power loss (W)
- I — Drain current (A)
- Rds(on) — On-state drain-source resistance (Ω)
Practical Notes
Rds_on increases with temperature, typically doubling between 25°C and 125°C for silicon MOSFETs. Always use the Rds_on value at your expected junction temperature, not the room temperature value from the datasheet summary. For paralleled MOSFETs, Rds_on divides by the number of devices, naturally sharing current due to positive temperature coefficient.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| P | Power | W | µW, mW, W, kW |
| I | Drain Current | A | pA, nA, µA, mA, A, kA |
| Rds | Rds(on) | mΩ | mΩ, Ω, kΩ, MΩ |
Step by step
- 1. What you know: Drain Current 2 A, Rds(on) 50 mΩ
- 2. The relation: P = I² × Rds(on)
- 3. Substitute: I = 2 A, Rds = 50 mΩ
- 4. Result: Power = 0.2 W
Related quantities from the same inputs
- P = I² × R = 0.2 W
Worked examples
Minimum range
Given: Drain Current 2 mA, Rds(on) 0.1 mΩ
Result: Power = 4 × 10⁻⁴ µW
Low range
Given: Drain Current 20 mA, Rds(on) 1 mΩ
Result: Power = 0.4 µW
Typical
Given: Drain Current 2 A, Rds(on) 50 mΩ
Result: Power = 0.2 W
High range
Given: Drain Current 100 A, Rds(on) 0.5 Ω
Result: Power = 5 kW
Maximum range
Given: Drain Current 1 kA, Rds(on) 5 Ω
Result: Power = 5000 kW
Solving for each variable
Solve for Power
Drain Current 2 mA, Rds(on) 0.1 mΩ → 4 × 10⁻⁴ µW
Solve for Drain Current
Power 10 mW, Rds(on) 0.1 mΩ → 10 A
Solve for Rds(on)
Power 10 mW, Drain Current 2 mA → 2.5 kΩ
How Power changes with Drain Current
| Drain Current (input) | Power (result) |
|---|---|
| 0.2 A | 2 mW |
| 0.5 A | 12.5 mW |
| 1 A | 50 mW |
| 1.5 A | 112.5 mW |
| 2 A | 0.2 W |
| 3 A | 0.45 W |
| 4 A | 0.8 W |
| 8 A | 3.2 W |
| 14 A | 9.8 W |
| 20 A | 20 W |
The same result in other units
| Unit | Value |
|---|---|
| µW | 200000 |
| mW | 200 |
| W | 0.2 |
| kW | 0.0002 |
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<p><a href="https://vbatpower.com/formulas/mosfet-loss/">MOSFET Conduction Loss</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate MOSFET Conduction Loss?
Use P = I² × Rds(on). With Drain Current 2 A, Rds(on) 50 mΩ, Power works out to 0.2 W.
How do you calculate mosfet conduction loss i squared rds on?
Rearrange for Power: with Drain Current 20 mA, Rds(on) 1 mΩ, Power is 0.4 µW.
What is the formula for MOSFET Conduction Loss?
The formula is P = I² × Rds(on). When a MOSFET is fully turned on, it behaves like a small resistor (Rds_on) between drain and source.
How do you find Drain Current when you know the other values?
Rearrange for Drain Current: with Power 10 mW, Rds(on) 0.1 mΩ, Drain Current is 10 A.
How do you find Rds(on) when you know the other values?
Rearrange for Rds(on): with Power 10 mW, Drain Current 2 mA, Rds(on) is 2.5 kΩ.
What units does MOSFET Conduction Loss use?
Power is shown in µW, mW, W, kW. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
All Semiconductors formulas →Need more features?
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