Step 1: Define Your Requirements

Before doing any calculations, define your electrical targets:

• Input Voltage (Vin)
• Output Voltage (Vout)
• Output Current (Iout)
• Switching Frequency (f)
• Target Ripple Current (ΔI)

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Example

Vin = 12V  
Vout = 5V  
Iout = 6A  
Switching Frequency = 250 kHz  
Ripple Current = 30% of Iout = 1.8A  

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Step 2: Calculate Inductance

The required inductance is determined by ripple current.

Basic Formula

$$L = \frac{(V_{in} – V_{out}) \cdot D}{\Delta I \cdot f}$$L=ΔI⋅f(Vin​−Vout​)⋅D​

Where:

• D = duty cycle = Vout / Vin
• ΔI = ripple current
• f = switching frequency

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Example Calculation

D = 5 / 12 = 0.417

L = (12 - 5) × 0.417 / (1.8 × 250,000)
L ≈ 6.5 µH

👉 In practice, you might round to a standard value like 6.8 µH or 10 µH

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Step 3: Understand Ripple Current Tradeoffs

Ripple current is one of the most important design knobs.

Lower Ripple:

• Lower losses
• Lower EMI
• Larger inductor

Higher Ripple:

• Smaller size
• Higher losses
• More stress on components

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Rule of Thumb

ΔI = 20% to 40% of Iout

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Step 4: Select Core Type and Material

This is where real engineering decisions begin.

Common Core Types

• E-core (EE, ETD) → balanced, widely used
• Toroid → low EMI, compact
• EFD / Low-profile → space-constrained designs

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Material Selection

• Ferrite → best for high frequency (most common)
• Iron Powder → good for distributed gap
• Amorphous / Nano → high performance, higher cost

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👉 Most buck converters use ferrite with a gap

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Step 5: Avoid Core Saturation

Inductors fail when the core saturates.

Key Concept

Magnetic flux density must stay below material limits:

B < Bsat

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What causes saturation?

• High current
• Too small core
• Too little gap

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Fixes:

• Increase core size
• Add/increase gap
• Use different material

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Step 6: Choose Wire Size (Current Handling)

Wire must handle current without excessive heating.

Key Parameter:

Current Density (J)

Typical values:

3 to 6 A/mm²

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Tradeoffs

• Smaller wire → easier winding, higher loss
• Larger wire → lower loss, harder to fit

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Skin Effect (Important at High Frequency)

At high frequencies:

• Current flows near surface
• Effective resistance increases

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Solutions:

• Litz wire
• Multiple parallel strands
• Foil windings

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Step 7: Estimate Losses

Total loss =

Core Loss + Copper Loss

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Core Loss depends on:

• Frequency
• Flux density
• Material

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Copper Loss:

$$P = I^2 \cdot R$$P=I2⋅R

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👉 Minimizing losses improves efficiency and temperature.

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Step 8: Check Temperature Rise

Temperature rise determines reliability.

Influenced by:

• Total losses
• Core size
• Airflow

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Rule of Thumb

ΔT < 40°C

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If temperature is too high:

• Increase core size
• Reduce current density
• Improve airflow

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Step 9: Balance Design Tradeoffs

There is no perfect design.

You must balance:

• Size
• Efficiency
• Cost
• Temperature
• Availability

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Examples

• Smaller → hotter
• Cooler → larger
• Cheaper → less efficient

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Common Mistakes

• Choosing inductance too low → excessive ripple
• Ignoring saturation limits
• Underestimating temperature rise
• Using incorrect wire size
• Not considering manufacturability

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The Hard Part (Reality Check)

Everything above is just the beginning.

A real design requires:

• Core geometry
• Gap optimization
• Winding layout
• Thermal estimation
• Manufacturable drawings
• BOM generation

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👉 This is where most engineers lose time.

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🚀 Faster Way: Generate Your Design Automatically

Instead of manually iterating through all these steps…

You can generate:

• Complete inductor design
• CAD model (SolidWorks)
• Manufacturing drawing
• Bill of Materials
• Performance estimates

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👉 Get your design here:

Design Your Inductor Now

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Final Thoughts

Inductor design is a balance of physics, constraints, and engineering judgment.

Once you understand the fundamentals, the challenge becomes execution — turning requirements into a real, buildable part.

That’s exactly what this tool is designed to do.