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Synchronous Buck MOSFET Power Loss Calculator

Synchronous buck voltage regulators power microprocessors, GPUs, and telecom ASIC rails with high step-down ratios, where MOSFET thermal losses dominate overall efficiency.

Operating DC input voltage.

Core rail output voltage.

Continuous DC output current.

PWM clock frequency.

Hot on-resistance of the high-side control switch.

Hot on-resistance of the low-side synchronous rectifier.

Voltage-current crossover rise time during turn-on.

Crossover fall time during turn-off.

Calculated Result
1.63 W

Total MOSFET Dissipation

Total MOSFET Power Loss

1.63 W

High-Side Switching Loss

0.99 W

Low-Side Conduction Loss

0.51 W

High-Side Conduction Loss

0.13 W

MOSFET Loss % of Output

8.31%

Duty Cycle (D)

10.0%

Calculation Breakdown

  1. Conduction Loss DistributionHS Conduction = D × I² × R_hs = 0.1 × 15² × 6mΩ = 0.13 W; LS Conduction = (1 - D) × I² × R_ls = 0.51 W
  2. High-Side V-I Overlap Switching LossP_sw = 0.5 × V_in × I_out × (t_r + t_f) × f_sw = 0.5 × 12 × 15 × (22ns) × 500000 = 0.99 W

MOSFET Power Dissipation Breakdown (W)

Interactive visualization based on your current inputs

Power (W)
0.02.14.26.28.3HS ConductionLS ConductionHS SwitchingTotal DissipationEff Impact (%)Loss MechanismPower (W)

What Is the Synchronous Buck MOSFET Power Loss Calculator?

The Synchronous Buck MOSFET Power Loss Calculator models the electrical and thermal dissipation across power semiconductors in step-down converters.

How Does the Synchronous Buck MOSFET Power Loss Calculator Work?

It computes duty cycle fractions, calculates I²R channel losses across high-side and low-side FETs, and computes transitional switching overlap energy.

Synchronous Buck MOSFET Power Loss Calculator Formula & Variables

The core mathematical equation utilized by this calculator is expressed as:

P_{cond,hs} = D I_{out}^2 R_{DS(on)}, \quad P_{sw,hs} = \frac{1}{2} V_{in} I_{out} (t_r + t_f) f_{sw}, \quad P_{cond,ls} = (1 - D) I_{out}^2 R_{DS(on),ls}

Decomposition of semiconductor losses into continuous channel resistance dissipation and transitional V-I crossover energy.

How to Use the Synchronous Buck MOSFET Power Loss Calculator

  1. Input operating input/output voltages and output load current.
  2. Specify PWM switching frequency and MOSFET hot R_DS(on) values.
  3. Enter high-side switching transition times (t_r and t_f).

Step-by-Step Example Calculation

12V-to-1.2V Point-of-Load 15A Buck Stage

Input Values:

inputVoltageVin:12
outputVoltageVout:1.2
outputCurrentIout:15
switchingFrequencyKhz:500
highSideRdsOnMilliOhms:6
lowSideRdsOnMilliOhms:2.5
highSideRiseTimeNs:12
highSideFallTimeNs:10
Worked Steps: Consumes 0.14 W HS conduction, 0.51 W LS conduction, and 0.99 W HS switching, totaling 1.63 W MOSFET loss (8.3% efficiency penalty).

Understanding Your Result

Total MOSFET Dissipation: Combined heat generated by the power stage in Watts.

High-Side vs Low-Side Losses: Detailed split between switching and conduction components.

Efficiency Impact: Direct conversion efficiency percentage penalty.

Factors That Affect the Result

  • Higher output currents scale conduction loss quadratically (I²).
  • Faster gate drive switching times decrease overlap duration and reduce switching loss.

When Should You Use This Calculator?

  • Power supply MOSFET selection, heatsink sizing, VRM thermal design, and power efficiency optimization.

Assumptions & Limitations

  • Assumes linear V-I switching crossover transitions and neglects body diode reverse recovery and gate drive losses.

Frequently Asked Questions

Calculation Accuracy & Reference Note

Based on Infineon and Texas Instruments Power Management application notes.

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