MOSFET Power Dissipation Calculator

A MOSFET is a transistor used in power electronics to switch or regulate electrical current — and the heat it generates directly limits how hard you can push it. Enter your Drain-Source Current (IDS), On-State Resistance (RDS(on)), Duty Cycle, and Switching Frequency into the MOSFET Power Dissipation Calculator to find the Total Power Loss in watts. Optionally include switching losses (via Bus Voltage, Rise Time, and Fall Time) and gate charge losses to get a full breakdown of Conduction Loss, Switching Loss, and Gate Charge Loss — plus Junction Temperature and Required Heatsink Thermal Resistance for thermal sizing.

A

Current flowing through the MOSFET when ON

mΩ

MOSFET resistance when fully turned ON

%

Percentage of time MOSFET is ON

Hz

How often the MOSFET switches per second

V

Supply voltage across the MOSFET

ns

Time for voltage to rise during turn-on

ns

Time for voltage to fall during turn-off

nC

Total charge required to turn on the gate

V

Voltage applied to the gate

°C

Operating ambient temperature

°C

Maximum allowable junction temperature

°C/W

Thermal resistance from junction to case

Results

Total Power Loss

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Conduction Loss

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Switching Loss

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Gate Charge Loss

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Required Heatsink Thermal Resistance

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Junction Temperature

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Frequently Asked Questions

What is MOSFET power dissipation and why is it important?

MOSFET power dissipation is the electrical power converted to heat during operation. It includes conduction losses when the MOSFET is ON, switching losses during transitions, and gate charge losses. Understanding power dissipation is crucial for thermal management and preventing device failure.

How do I calculate conduction losses in a MOSFET?

Conduction losses are calculated using P_cond = I²DS × RDS(on) × D, where IDS is the drain current, RDS(on) is the on-state resistance, and D is the duty cycle. This represents power lost due to resistance when current flows through the MOSFET.

What are switching losses and when do they occur?

Switching losses occur during the transition between ON and OFF states. They're calculated as P_sw = 0.5 × VIN × IDS × (tr + tf) × fsw, where tr and tf are rise and fall times. Higher switching frequencies increase these losses significantly.

When do I need to calculate heatsink thermal resistance?

Calculate heatsink thermal resistance when the total power loss could cause the junction temperature to exceed its maximum rating. The heatsink helps dissipate heat to keep the MOSFET within safe operating temperatures.

How does switching frequency affect MOSFET power losses?

Higher switching frequencies increase both switching losses and gate charge losses proportionally, as both occur once per switching cycle. Conduction losses remain unchanged. This is why high-frequency applications require careful thermal design.

What is RDS(on) and how does it affect power dissipation?

RDS(on) is the drain-to-source resistance when the MOSFET is fully turned ON. Lower RDS(on) values reduce conduction losses, making the MOSFET more efficient. This parameter varies with temperature and gate voltage.

How do I determine the maximum safe junction temperature?

Maximum junction temperature is specified in the MOSFET datasheet, typically 150°C to 175°C. Operating below this temperature ensures reliability and prevents thermal runaway. Always include safety margins in your thermal design.

What factors influence gate charge losses?

Gate charge losses depend on gate charge (QG), gate drive voltage (VGS), and switching frequency. The formula is P_gate = QG × VGS × fsw. Using lower gate drive voltages can reduce these losses but may affect switching performance.