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Switch-Mode Buck Converter Inductor & Capacitor Sizing Calculator

A buck converter is a high-efficiency DC-DC step-down switching regulator that converts a higher input voltage to a regulated lower output voltage.

Nominal DC input voltage.

Regulated DC output voltage.

Maximum continuous DC load current.

Converter switching frequency in kilohertz.

Target peak-to-peak inductor ripple current (typically 20% to 40% of I_out).

Allowable peak-to-peak output voltage ripple in millivolts.

Calculated Result
5.32 µH

Required Inductor (L)

Required Inductance (L)

5.32 µH

Minimum Output Cap (C_out)

11.2 µF

Peak Inductor Saturation Current

3.45 A

Inductor Ripple Current (ΔI_L)

0.9 A

Switch Duty Cycle (D)

30.6%

Switching Frequency

500 kHz

Calculation Breakdown

  1. Switch Duty RatioD = V_out / (V_in × η) = 3.3 V / (12 V × 0.90) = 30.6%
  2. Inductor Sizing FormulaL = [3.3 × (12 - 3.3)] / (0.9 A × 500000 Hz × 12) = 5.32 µH
  3. Output Capacitor Sizing for RippleC_out = 0.9 A / (8 × 500000 Hz × 0.02 V) = 11.2 µF

Buck Converter Design Sizing

Interactive visualization based on your current inputs

Value
0.07.7152331Inductance (µH)Capacitance (µF)Peak Saturation (A)Duty Cycle (%)ComponentValue

What Is the Switch-Mode Buck Converter Inductor & Capacitor Sizing Calculator?

A buck converter is a switched-mode power supply topology that steps down voltage while stepping up current with high electrical efficiency (typically 85% to 95%).

How Does the Switch-Mode Buck Converter Inductor & Capacitor Sizing Calculator Work?

A semiconductor switch pulses energy into an inductor-capacitor low-pass filter. The duty cycle D ≈ V_out / V_in controls the output voltage.

Switch-Mode Buck Converter Inductor & Capacitor Sizing Calculator Formula & Variables

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

L = \frac{V_{\text{out}} (V_{\text{in}} - V_{\text{out}})}{\Delta I_L \cdot f_{\text{sw}} \cdot V_{\text{in}}}, \quad C_{\text{out}} = \frac{\Delta I_L}{8 \cdot f_{\text{sw}} \cdot \Delta V_{\text{out}}}, \quad D = \frac{V_{\text{out}}}{V_{\text{in}} \cdot \eta}

Sizes power inductor L and filter capacitor Cout for continuous conduction mode step-down DC-DC switching buck regulators.

How to Use the Switch-Mode Buck Converter Inductor & Capacitor Sizing Calculator

  1. Enter input and target output voltage.
  2. Specify maximum load current and controller switching frequency.
  3. Input ripple targets to compute required L and C values.

Step-by-Step Example Calculation

12V to 3.3V / 3A Buck Converter at 500 kHz

Input Values:

inputVoltageVin:12.0
outputVoltageVout:3.3
outputCurrentIoutAmps:3.0
switchingFrequencyKhz:500
inductorCurrentRipplePercent:30
outputVoltageRippleMv:20
Worked Steps: Requires a 5.32 µH inductor rated for ≥ 3.45 A saturation, and a minimum output capacitance of 11.3 µF at 30.6% duty cycle.

Understanding Your Result

Required Inductance: Minimum inductance in microhenries (µH) to limit ripple current.

Minimum Capacitance: Output capacitance in µF needed to absorb ripple charge.

Peak Current: Minimum saturation current rating required for the power inductor.

Factors That Affect the Result

  • Higher switching frequencies decrease required L and C sizes at the expense of increased MOSFET switching losses.

When Should You Use This Calculator?

  • Power supply design, FPGA/microcontroller power rails, automotive USB chargers, and battery management systems.

Assumptions & Limitations

  • Assumes Continuous Conduction Mode (CCM) and low capacitor Equivalent Series Resistance (ESR).

Frequently Asked Questions

Calculation Accuracy & Reference Note

Standard switch-mode power supply design formulation.

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