One of the best ways to understand magnetic design is to work through a practical example.

In this article we will examine the design process for a buck converter inductor used to convert 48V DC into 12V DC at 10A output current.

The goal is not to create a production-ready design, but to demonstrate the engineering thought process behind magnetic component selection.

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Design Requirements

For this example, assume:

Input Voltage:

48V

Output Voltage:

12V

Output Current:

10A

Switching Frequency:

200 kHz

Target Ripple Current:

30% of output current

Maximum Temperature Rise:

40°C

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Step 1: Determine Ripple Current

A common design target is:

30% ripple current.

Ripple current:

10A × 0.30 = 3A

Therefore:

ΔI = 3A

Ripple current directly affects:

• Peak current
• RMS current
• Copper losses
• Saturation margin

👉 Related Guide: Ripple Current Explained

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Step 2: Calculate Required Inductance

For a buck converter:

Duty Cycle:

12V / 48V

= 0.25

The required inductance is approximately:

L=\frac{(V_{in}-V_{out})D}{\Delta I f_s}

Substituting the values gives:

Approximately 15 µH

This becomes the target inductance.

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Step 3: Determine Peak Current

Peak current is:

I_{peak}=I_{DC}+\frac{\Delta I}{2}

Result:

10A + 1.5A

= 11.5A

This value is critical for saturation analysis.

👉 Related Guide: Understanding Magnetic Saturation

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Step 4: Determine Energy Storage

Stored energy:

E=\frac{1}{2}LI^2

Using:

15 µH

11.5A peak current

Results in approximately:

1 mJ

This energy must be stored safely without excessive saturation.

👉 Related Guide: How to Calculate Inductor Energy Storage

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Step 5: Select Core Material

Several materials could work:

• Ferrite
• Powdered Iron
• Nanocrystalline

For this example:

Ferrite is selected because:

• Low losses at 200 kHz
• Widely available
• Good efficiency

👉 Related Guide: How to Choose the Right Core Material

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Step 6: Select Core Size

The core must provide:

• Adequate energy storage
• Acceptable temperature rise
• Manufacturable winding space

Possible candidates:

• ETD29
• ETD34
• E30
• PQ32

At this stage multiple candidates are usually evaluated.

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Step 7: Determine Air Gap

An air gap is required to:

• Store energy
• Prevent saturation
• Increase current capability

👉 Related Guide: Air Gap Design in Power Inductors

The exact gap depends on the selected core and target inductance.

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Step 8: Select Wire Size

The winding must carry:

10A average current

while minimizing losses.

Possible choices include:

• AWG16
• AWG15
• Parallel AWG18

The final choice depends on:

• Fill factor
• Temperature rise
• Manufacturability

👉 Related Guide: Choosing Wire Gauge for Power Inductors

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Step 9: Evaluate DCR

The design should minimize:

• Copper losses
• Voltage drop
• Heating

👉 Related Guide: What Is DCR in an Inductor?

Lower DCR generally improves efficiency.

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Step 10: Evaluate Temperature Rise

Losses generate heat through:

• Copper losses
• Core losses

👉 Related Guide: Inductor Temperature Rise Explained

The design target is:

Less than 40°C rise

under worst-case operating conditions.

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What Engineers Would Optimize Next

A real design process would continue by optimizing:

• Core geometry
• Air gap
• Wire size
• DCR
• Temperature rise
• Cost

This iterative process often evaluates multiple candidate solutions.

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How Automated Design Tools Help

Modern magnetic design software can evaluate hundreds of possible designs automatically.

Instead of manually calculating each option, engineers can compare:

• Core families
• Air gaps
• Wire sizes
• Temperature rise
• Efficiency

and identify the best solution quickly.

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Conclusion

This example demonstrates the engineering process behind designing a practical buck converter inductor.

The final design depends on balancing:

• Inductance
• Current rating
• Energy storage
• Saturation margin
• Thermal performance
• Manufacturability

Successful magnetic design always involves evaluating multiple tradeoffs rather than optimizing a single parameter.

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