MOSFET Calculator
Calculate drain current and power dissipation for MOSFETs
Volts (V)
Ohms (Ω) - typically 0.01-1 Ω for power MOSFETs
How to Use This Calculator
Enter Drain-Source Voltage
Enter the voltage across the drain and source terminals (VDS) in volts.
Enter On-Resistance
Enter the drain-source on-resistance (RDS(on)) from the MOSFET datasheet in ohms.
Get Results
Click calculate to see drain current and power dissipation. This assumes MOSFET is fully on (ohmic region).
Formula
ID = VDS / RDS(on)
P = ID × VDS
Where:
- ID = Drain current (A)
- VDS = Drain-source voltage (V)
- RDS(on) = Drain-source on-resistance (Ω)
- P = Power dissipation (W)
Note: This formula applies to MOSFETs in the ohmic (linear) region when fully turned on. Actual MOSFET behavior is more complex and depends on gate voltage, drain voltage, and operating region.
Example:
VDS = 12 V, RDS(on) = 0.1 Ω
ID = 12 / 0.1 = 120 A
P = 120 × 12 = 1,440 W
About MOSFET Calculator
The MOSFET Calculator provides simplified calculations for MOSFET drain current and power dissipation. MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are widely used in power electronics for switching applications. This calculator helps estimate current and power for MOSFETs in the ohmic (linear) region when fully turned on.
When to Use This Calculator
- Power Supply Design: Estimate MOSFET current and power in switching circuits
- Heat Sink Sizing: Calculate power dissipation for thermal design
- Educational Purposes: Learn about MOSFET operation
Why Use Our Calculator?
- ✅ Quick Estimates: Fast calculation for initial design
- ✅ Easy to Use: Simple interface
- ✅ Free Tool: No registration required
Important Notes
Simplified Model: This calculator uses a simplified model assuming the MOSFET is fully on and in the ohmic region. Real MOSFET behavior is more complex and depends on:
- Gate-source voltage (VGS)
- Operating region (cutoff, ohmic, saturation)
- Temperature (RDS(on) increases with temperature)
- Drain current (for saturation region)
Tips for Accurate Results
- Use RDS(on) from MOSFET datasheet
- This calculator assumes MOSFET is fully on
- Consider temperature effects on RDS(on)
- For saturation region, use different formulas
- Always use heat sink for high power dissipation
Frequently Asked Questions
What is RDS(on)?
RDS(on) is the drain-source on-resistance when the MOSFET is fully turned on. It's a key parameter that determines power dissipation and current capability. Lower RDS(on) means lower losses.
What are MOSFET operating regions?
MOSFETs have three regions: cutoff (off), ohmic/linear (fully on, acts like resistor), and saturation (partially on, constant current). This calculator assumes ohmic region.
Why is power dissipation important?
Power dissipation creates heat. MOSFETs must be kept within their temperature limits. High power dissipation requires heat sinks to prevent overheating and failure.
Does RDS(on) change with temperature?
Yes, RDS(on) increases with temperature. Datasheets typically specify RDS(on) at 25°C. At higher temperatures, resistance increases, causing more power dissipation and potential thermal runaway.